NON- EMERGENCY SITUATIONS chapter .1Management of RADIOACTIVITY in DRINKING-WATER
Management of RADIOACTIVITY in DRINKING-WATER Management of radioactivity in drinking-water ISBN 978-92-4-151374-6 © World Health Organization 2018 Some rights reserved. This work is available under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 IGO licence (CC BY-NC-SA 3.0 IGO; https://creativecommons.org/licenses/by-nc-sa/3.0/igo). Under the terms of this licence, you may copy, redistribute and adapt the work for non-commercial purposes, provided the work is appropriately cited, as indicated below. In any use of this work, there should be no suggestion that WHO endorses any specific organization, products or services. The use of the WHO logo is not permitted. If you adapt the work, then you must license your work under the same or equivalent Creative Commons licence. If you create a translation of this work, you should add the following disclaimer along with the suggested citation: “This translation was not created by the World Health Organization (WHO). WHO is not responsible for the content or accuracy of this translation. The original English edition shall be the binding and authentic edition”. Any mediation relating to disputes arising under the licence shall be conducted in accordance with the mediation rules of the World Intellectual Property Organization. Suggested citation. Management of radioactivity in drinking-water. Geneva: World Health Organization; 2018. Licence: CC BY-NC-SA 3.0 IGO. Cataloguing-in-Publication (CIP) data. CIP data are available at http://apps.who.int/iris. Sales, rights and licensing. To purchase WHO publications, see http://apps.who.int/bookorders. To submit requests for commercial use and queries on rights and licensing, see http://www.who.int/about/licensing. Third-party materials. If you wish to reuse material from this work that is attributed to a third party, such as tables, figures or images, it is your responsibility to determine whether permission is needed for that reuse and to obtain permission from the copyright holder. The risk of claims resulting from infringement of any third-party-owned component in the work rests solely with the user. General disclaimers. The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of WHO concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted and dashed lines on maps represent approximate border lines for which there may not yet be full agreement. The mention of specific companies or of certain manufacturers’ products does not imply that they are endorsed or recommended by WHO in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. All reasonable precautions have been taken by WHO to verify the information contained in this publication. However, the published material is being distributed without warranty of any kind, either expressed or implied. The responsibility for the interpretation and use of the material lies with the reader. In no event shall WHO be liable for damages arising from its use. Printed in Switzerland. Design and layout by Paprika, Annecy, France. TABLE OF CONTENTS LIST OF TABLES AND FIGURES IX FOREWORD X ACKNOWLEDGMENTS XII ABBREVIATIONS XIV GLOSSARY XV 1. NON-EMERGENCY SITUATIONS 1 1.1 Background .................................................................................................................................................................................................................................2 1.1.1 Are radionuclides in drinking-water likely to be a public health risk in non-emergency situations ? ............................2 1.1.2 What are the possible sources of radionuclides in drinking-water in non-emergency situations ? ...............................3 1.1.3 How do naturally occurring radionuclides enter into drinking-water ?......................................................................................................4 1.1.4 When should radionuclides in drinking-water be considered in non-emergency situations ? ..........................................5 1.2 Purpose and scope of the Guidelines for drinking‑water quality ......................................................................................................... 6 1.2.1 What is the purpose of the Guidelines for drinking-water quality ? .............................................................................................................6 1.2.2 What guidance does WHO provide on radionuclides in drinking-water ? ............................................................................................8 1.2.3 What situations can the GDWQ be used for ? ..................................................................................................................................................................8 1.2.4 Are the radiological criteria in the GDWQ mandatory ? ..........................................................................................................................................9 1.2.5 Why do the criteria provided in the GDWQ not apply during a radiological or nuclear emergency ? ........................9 1.2.6 Are there any international criteria for radionuclides in bottled and packaged drinking-water ? ....................................9 1.2.7 Should naturally occurring radionuclides and human-made radionuclides present in drinking-water be managed differently ?............................................................................................................................................................................................................................ 10 1.3 Approach adopted by WHO for assessing the public health risk from radionuclides in drinking‑water .................11 1.3.1 What are the criteria used in the GDWQ for assessing health risks from radionuclides in drinking-water ? ........ 11 1.3.2 What is the individual dose criterion of 0.1 mSv y-1 ? ............................................................................................................................................... 12 1.3.3 What purpose do the screening levels serve and how should they be used ? .................................................................................... 12 1.3.4 What purpose do the guidance levels for radionuclides serve and how should they be used ?................................. 13 1.3.5 Do the guidance levels need to be adjusted for children ? ...............................................................................................................................14 1.3.6 What is the reference level (1 mSv y-1) and how does it relate to the individual dose criterion (0.1 mSv y-1) for drinking-water ?...................................................................................................................................................................................................................................15 . VMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.4 Measuring radionuclides in drinking‑water ....................................................................................................................................................... 16 1.4.1 At what points in the water supply chain should measurements of radionuclides in drinking-water be made ? ................................................................................................................................................................................................................................................................. 16 1.4.2 With what frequency should measurements of radionuclides in drinking-water be made ? ...........................................17 1.4.3 Are there any radionuclides that are not detected by standard gross alpha and gross beta screening methods ? ......................................................................................................................................................................................................................................................... 19 1.5 How to apply the GDWQ methodology for radionuclides in drinking‑water .............................................................................. 21 1.5.1 If a screening level is exceeded for one or a few drinking-water samples, does this mean that the radiation dose will be greater than the individual dose criterion of 0.1 mSv y-1 ? ................................................................................................... 21 1.5.2 Is any action required if the screening levels are not exceeded ? ............................................................................................................ 22 1.5.3 What further action is required if either of the screening levels is exceeded for a drinking-water sample ? .. 23 1.5.4 What is the reason for subtracting the contribution of potassium-40 from gross beta activity when the gross beta activity concentration exceeds the screening level? How can it be performed ? ....................................................................25 1.5.5 How to identify what radionuclides in the drinking-water are contributing to screening levels being exceeded ? ......................................................................................................................................................................................................................................................25 1.5.6 How to assess if the individual dose criterion of 0.1 mSv y-1 has been exceeded using measurements of individual radionuclides in drinking-water ? ...................................................................................................................................................................... 26 1.5.7 If the activity concentrations in drinking-water for the radionuclides measured do not exceed the guidance levels, does this mean that no further action is required ? ................................................................................................................................ 28 1.5.8 If the 0.1 mSv y-1 individual dose criterion is exceeded, does this mean that the drinking-water is unsuitable for consumption ? .................................................................................................................................................................................................................................... 28 1.5.9 What is the next step if a guidance level is exceeded or the sum across radionuclides exceeds unity, i.e. the individual dose criterion of 0.1 mSv y-1 is exceeded ? .......................................................................................................................... 29 1.5.10 What are the considerations for establishing national standards based on the GDWQ and the International Basic Safety Standards ? ............................................................................................................................................................................................................... 32 1.5.11 What are the possible options for reducing activity concentrations of radionuclides in drinking-water ? ..........35 1.6 Radon in drinking‑water .................................................................................................................................................................................................37 1.6.1 How does radon get into drinking-water ? ........................................................................................................................................................................37 1.6.2 Do national standards for radon in drinking-water need to be established ? .................................................................................37 1.6.3 At what points in the water supply chain should measurements of radon in drinking-water be made ? ............ 38 1.6.4 What methods can be used for sampling and measuring radon in drinking-water supplies ? ..................................... 39 1.6.5 How can radon in drinking-water be managed when radon concentrations in the source water are high ? ... 39 VI . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 2. EMERGENCY SITUATIONS 41 2.1 Background on emergency situations and criteria for managing drinking‑water quality .................................................42 2.1.1 What is a radiation emergency situation ? .........................................................................................................................................................................42 2.1.2 Are radionuclides in drinking-water likely to remain a long-term public health risk after a nuclear or radiological emergency ? ..................................................................................................................................................................................................................42 2.1.3 When does an emergency situation end and what does this mean with respect to drinking-water quality ? 43 2.1.4 Are there any international standards and criteria that apply for drinking-water quality in emergency situations ? ..................................................................................................................................................................................................................................................... 44 2.2 Health risks from drinking‑water in the event of a nuclear or radiological emergency ....................................................45 2.2.1 What radionuclides are likely to be of concern in drinking-water during a nuclear or radiological emergency ? ................................................................................................................................................................................................................................................45 2.2.2 Do children require stricter protection than adults when establishing criteria for the consumption of drinking-water after a nuclear or radiological emergency ? ..........................................................................................................................47 2.2.3 How are health risks from radionuclides in drinking-water likely to compare to those from other exposure pathways in nuclear or radiological emergencies ? ...............................................................................................................................................47 2.3 Measuring radionuclides in drinking‑water in an emergency situation .........................................................................................49 2.3.1 What screening methods can be used in nuclear or radiological emergencies to measure radionuclides in drinking-water ? .................................................................................................................................................................................................................................. 49 2.3.2 During a nuclear or radiological emergency, what types of water source are likely to be affected ? ....................50 2.3.3 During a nuclear or radiological emergency, which water sources are a priority for monitoring ? .............................51 2.4 Managing exceedances of criteria for drinking‑water in emergency situations ......................................................................52 2.4.1 How are operational intervention levels for drinking-water used in the event of a nuclear or radiological emergency ?.................................................................................................................................................................................................................................................52 2.4.2 What actions can be considered if the criteria for drinking-water in emergency situations are exceeded ? Are there any special actions for small water supplies, including community supplies ? ..................................................54 3. SUPPORTING INFORMATION 57 3.1 Does boiling water reduce the exposure from radionuclides in drinking‑water ? ..................................................................58 3.2 How effective are water treatment options in removing radionuclides from drinking‑water ? .....................................59 3.3 If radionuclides are removed from drinking‑water by treatment, where do they end up in the treatment process? Could there be wastes from water treatment processes that need to be handled as radioactive waste ? .........................62 3.4 What are the health risks to people working in water treatment activities that have processed water containing radionuclides ? ............................................................................................................................................................................................65 3.5 What methods can be used for measuring radionuclides in drinking‑water supplies ? ....................................................67 . VIIMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 4. CASE STUDIES 73 4.1 Brazil ............................................................................................................................................................................................................................................. 74 4.2 Canada .......................................................................................................................................................................................................................................78 4.3 Jordan ......................................................................................................................................................................................................................................... 81 4.4 Sweden...................................................................................................................................................................................................................................... 86 4.5 Japan...........................................................................................................................................................................................................................................90 REFERENCES 95 References ..................................................................................................................................................................................................................................... 96 ANNEx 1 CALCULATION OF DOSES AND GUIDANCE LEVELS FOR SPECIFIC NON-EMERGENCY SITUATIONS 101 A.1 Doses to children from the consumption of drinking‑water .............................................................................................................. 102 A.2 Drinking‑water consumption rates ..................................................................................................................................................................... 102 A.3 Ingestion dose coefficients for children ........................................................................................................................................................... 103 A.4 Guidance levels for specific situations .............................................................................................................................................................104 References .....................................................................................................................................................................................................................................................................104 VIII . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER LIST OF TABLES AND FIGURES Figure 1.1. Interrelationships among the individual chapters of the GDWQ in ensuring drinking‑water safety .............7 Figure 1.2. Flowchart for measurement of radionuclides in drinking‑water ......................................................................................24 Table 1.1. Summary of WHO guidance levels for common radionuclides in drinking‑water .................................................26 Table 1.2. Guidance levels for common radionuclides .................................................................................................................................... 29 Table 1.3. Summary of suggested actions for given levels of individual dose .................................................................................32 Table 1.4. Framework for setting a national standard or reference level ..............................................................................................33 Table 2.1. Radionuclides potentially relevant for drinking‑water following a nuclear or radiological emergency ..46 Figure 2.1. Staged approach for applying the OILs in emergency situations .....................................................................................53 Table 3.1. Surface and groundwater characteristics ...........................................................................................................................................59 Table 3.2. Water treatment performance ..................................................................................................................................................................60 Table 3.3. Main features of the different methods to measure radionuclides in drinking‑water ..........................................70 Figure 4.1. A simplistic schematic of the Disi‑Mudawarra conveyance system to Amman ......................................................83 Table 4.1. Intervention protocol to be followed in Jordan after radionuclide monitoring in drinking‑water .................84 Table A.1. Default consumption rates of drinking‑water for children ................................................................................................... 102 Table A.2. Ingestion dose coefficients for different ages .............................................................................................................................. 103 . IXMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER FOREWORD Rationale for this document The World Health Organization Guidelines for drinking-water quality (WHO GDWQ) (WHO, 2017a) provide the basis for the development of national regulations and standards and risk management strategies to ensure safe drinking-water. Although they include guidance related to the radiological aspects of drinking-water in non-emergency situations (see Chapter 9 developed in the 2011 edition and retained in the 2017 edition), practical advice was requested by Member States to support stakeholders in the interpretation and implementation of the GDWQ in order to take appropriate action on these aspects. Accordingly, this guidance on management of radioactivity in drinking-water has been developed, taking into account the experience and knowledge gained with implementation of Chapter 9 of the GDWQ. This guidance will also facilitate the development of relevant national drinking-water standards and support their implementation. Further, in response to requests from Member States, additional guidance in the event of a nuclear or radiological emergency has been written with the aim of raising awareness on applicable international standards and criteria as well as facilitating the management of drinking-water supplies. Target audience The questions and answers (Q&As) in this document are intended for organizations that set or enforce standards related to, or manage risks from, radioactivity in drinking-water at both local and national levels. The document will also be useful to the agencies that may provide support on issues related to radioactivity in drinking-water. Therefore, the document will be useful to water suppliers, drinking-water regulators, radiation protection specialists, and emergency planners. The guidance is not written as communication material for members of the public, although it may be helpful in developing such materials. Description of this document This guidance on radiological aspects of drinking-water quality is written in the format of Q&As. Each question and associated answer is written to be largely stand-alone with links to other Q&As that provide additional relevant information; there is no need to read the document from start to finish. The document is divided into four sections: • Section 1 on non-emergency situations provides background information on the GDWQ, explains the approach adopted by WHO to assess the public health risks from radionuclides in drinking-water and aspects to support their management in these situations. Information on radon, including the assessment and management of risks, is provided in a separate section, as the assessment and management approach for radon is distinct compared to the other radionuclides. X . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER • Section 2 on emergency situations provides similar information included in the non-emergency section, but within an emergency context. • Section 3 provides supporting information that is largely common to both non-emergency and emergency situations, including information on treatment and analytical methods. • Section 4 includes case studies illustrating how some countries have managed radioactivity in drinking-water. The document also includes an Annex to support calculation of doses and guidance levels for specific non-emergency situations. For non-emergency situations, it is anticipated that the reader will use this guidance in conjunction with Chapter 9 of the GDWQ (WHO, 2017a); however, some information in the GDWQ is summarized within this guidance for convenience, to support practical implementation. . XIMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER ACKNOWLEDGMENTS This guidance is the result of collaboration between the Water, Sanitation, Hygiene and Health team and the Radiation Programme team, at the World Health Organization. WHO wishes to express its appreciation to all whose efforts made the production of this document possible, through the provision of their time, expertise and experience. A WHO Secretariat, comprising Jennifer De France, Maria Perez, Bruce Gordon and Emilie van Deventer served as the editorial group and coordinated the development of this document. WHO is particularly grateful to the lead writer, Joanne Brown, independent consultant (formerly with Public Health England) for her valuable advice and instrumental assistance to the editorial group during the process of drafting and reviewing this document. Koichi Ohno’s technical input in preparing for the first working group meeting is also gratefully acknowledged. Thanks are expressed to the following experts, who collectively contributed to the development of this document through participation in two working group meetings and further drafting and review: • Hamed Bakir, WHO Regional Office for the Eastern Mediterranean, Jordan • Jing Chen, Health Canada, Canada • John Fawell, Cranfield University, United Kingdom • Susan Kilani, Ministry of Water and Irrigation, Jordan • Nthabiseng Mohlala, National Nuclear Regulator, South Africa • Teofilo Monteiro, WHO Pan-American Health Organization, Peru • Koichi Ohno, formerly National Institute of Public Health, Japan • Kirlna Skeppström, formerly Swedish Radiation Safety Authority, Sweden • Barry Smith, Independent Consultant, United Kingdom • Katherine Snead, United States Environmental Protection Agency, United States of America • Lene Veiga, formerly Institute of Radiation Protection and Dosimetry, Brazil Thanks are also due to the working group participants from Brazil, Canada, Japan, Jordan and Sweden for developing the case studies included in Section 4. A number of experts and practitioners from both the drinking-water and radiation protection community contributed through peer review and in some cases, by providing additional text: • Mari Asami, National Institute of Public Health, Japan • Francesco Bochicchio, National Center for Radiation Protection and Computational Physics, Italy • Jane Bradley, Public Health England, United Kingdom • Tony Colgan, International Atomic Energy Agency, Austria • Joseph Cotruvo, Independent Consultant, United States of America • David Cunliffe, South Australia Health, Australia • Michael Davidson, Public Health England, United Kingdom XII . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER • Isabelle Dublineau, Institute for Radiological Protection and Nuclear Safety, France • Sybille Estier, Federal Office of Public Health, Switzerland • Mariza Ramalho Franklin, Institute of Radiation Protection and Dosimetry, Brazil • Klaus Gehrcke, Federal Office for Radiation Protection, Germany • Marc Gleizes, Institute for Radiological Protection and Nuclear Safety, France • Hans-Jürgen Grummt, German Environment Agency, Germany • Joanne Hunt, Drinking-Water Inspectorate, United Kingdom • Darryl Jackson, Independent Consultant, Australia • Christian Lucks, Federal Office for Radiation Protection, Germany • Kelly Jones, Public Health England, United Kingdom • Neil McColl, Public Health England, United Kingdom • Helgard Muller, Independent Consultant, South Africa • Svetlana Nestoroska-Madjunarova, International Atomic Energy Agency, Austria • Jan Pietersen, Midvaal Water Company, South Africa • Alain Rannou, Institute for Radiological Protection and Nuclear Safety, France • Donald Reid, Environment and Parks, Canada • David Sheehan, Coliban Water, Australia • Luís Simas, Water and Waste Services Regulation Authority, Portugal • Bo Thunholm, Geological Survey of Sweden, Sweden • Rick Tinker, Australian Radiation Protection and Nuclear Safety Agency, Australia • Christiane Wittwer, Federal Office for Radiation Protection, Germany • Muhd Noor M. Yunus, Atomic Energy Licensing Board Member, Malaysia Feedback was also provided by participants at three regional workshops jointly organized by WHO, IAEA and other partners. WHO gratefully acknowledges the financial support provided by the Department for International Development, United Kingdom, the Ministry of Health, Labour and Welfare, Japan and the Ministry of Water and Irrigation, Jordan. . XIIIMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER ABBREVIATIONS ALARA as low as reasonably achievable Bq becquerel BSS Basic Safety Standards EC European Commission FAO Food and Agricultural Organization of the United Nations GDWQ Guidelines for drinking-water quality IAEA International Atomic Energy Agency ICP-MS inductively-coupled plasma mass spectrometry ICRP International Commission on Radiological Protection IDC individual dose criterion ILO International Labour Organization LOD limit of detection mSv millisieverts NaI sodium iodine NEA Nuclear Energy Agency OECD Organisation for Economic Co-operation and Development OIL Operational Intervention Level PAHO Pan American Health Organization Sv sieverts UNEP United Nations Environment Programme UNSCEAR United Nations Scientific Committee on the Effects of Atomic Radiation WHO World Health Organization XIV . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER GLOSSARY Activity: See “radioactivity”. Activity concentration: Amount of radioactivity expressed by a unit of activity per unit volume, e.g. becquerel/litre or becquerel/kilogram. See also “radioactivity” and “becquerel”. Alpha particles: Two neutrons and two protons bound as a single particle that is emitted from the nucleus of certain radioactive isotopes in the process of decay or disintegration; a positively charged particle indistinguishable from the nucleus of a helium atom. Alpha particles can scarcely penetrate the dead outer layer of human skin so radionuclides that emit them are only hazardous if they are taken into the body, for example via inhalation or ingestion. Atoms: The smallest particles of a chemical element that retains its chemical properties. They are composed of particles distributed in a dense nucleus of positively-charged protons and electrically-neutral neutrons, surrounded by a cloud of negatively-charged electrons. Becquerel: The spontaneous disintegration of radioactive atoms is called “radioactivity” or just “activity”. The amount of radioactivity is measured as the number of spontaneous disintegrations per second. The becquerel (Bq) is the unit of activity in the International System of Units. It is equal to one disintegration per second. Beta particles: A negatively charged particle emitted from the nucleus of an atom, with mass equal to those of an electron. Beta particles may penetrate a centimetre or so of tissue, so radionuclides that emit them are hazardous to superficial tissues but not internal organs unless they are taken into the body via inhalation or ingestion. Conservative: An approach that deliberately chooses an option (e.g. an assumption) that is more likely to overestimate than to underestimate the risk. Consumption rate: Average quantity of an item consumed during a given time interval and expressed in an appropriate unit of measurement e.g. litres per day for drinking-water. Dose: In the context of this document, a measure of the energy deposited by radiation in a target. See also “effective dose”. Dose coefficients: Factors used to convert the amount of incorporated radioactive substances (radionuclide intake) to the dose in tissues or organs, or the whole-body dose. These factors (also called “dose conversion factors”) may depend on the radionuclide, the incorporation route (e.g. inhalation, ingestion), the chemical compound and the age of the person. Usually expressed as dose per unit intake, e.g. sieverts/becquerel. Dose conversion factor: See “dose coefficients”. Effective dose: Sum of the products of dose to each organ multiplied by a radiation-weighting factor and a tissue- weighting factor that takes into account the radiosensitivity of tissues and organs. Related term: “dose”. Emergency situation: In the context of this document, a situation which requires prompt action in order to avoid or reduce undesirable consequences from radiation exposure to humans and/or the environment. An emergency exposure situation may arise as a result of an accident, a malicious act or any other unexpected event. Emergency exposures can be to the public and to workers, such as those who may be exposed while taking actions to respond to the emergency. . XVMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Exposure: In the context of this document, the state or condition of being subjected to irradiation from a source outside the body (i.e. external exposure) or within the body (i.e. internal exposure). Exposure pathway: In the context of this document, a route by which radiation or radionuclides can reach humans and cause exposure. External exposure: See “exposure”. Gamma rays: Short wavelength electromagnetic radiation without mass or charge (i.e. photons) of nuclear origin; they are similar to X-radiation but emitted at very specific energies characteristic of the decaying atoms. Gamma rays can pass through the body, so radionuclides that emit them may be hazardous whether on the outside or the inside of the body. Gross alpha (activity concentration): Total activity of all alpha particle emitters, expressed in terms of unit of activity per unit of volume (e.g. becquerel /litre). The gross alpha screening measurements do not provide the identity of or activity concentration of specific alpha-emitting radionuclides. Gross beta (activity concentration): Total activity of all beta particle emitters excluding tritium, although other weak beta emitters are also excluded using most screening measurement techniques; expressed in terms of unit of activity per unit of volume (e.g. becquerel /litre). The gross beta screening measurements do not provide the identity or activity concentration of specific beta-emitting radionuclides. Groundwater: Water contained beneath the surface of the earth in rocks or subsoil, which may accumulate underground in aquifers. Guidance level: In the context of this document the activity concentration of a given radionuclide that, if present in drinking-water consumed throughout one year at a consumption rate of 2 litres per day would result in an individual dose of 0.1 millisievert (mSv). Half-life: The time taken for the quantity of a radionuclide to decrease by half as a result of radioactive decay. Hazard: A biological, chemical or physical agent that may cause harm to human health. Health effect: Changes in the health status of an individual or population, identifiable either by diagnostic or epidemiological methods. Individual dose criterion: In the context of this document, the criterion for assessing health risks from prolonged exposure to radionuclides in drinking-water. The individual dose criterion (IDC) is 0.1 millisievert (mSv) per one year’s consumption of drinking-water. In practice, this criterion is translated into two operational quantities: the screening levels and the guidance levels. See also “screening level” and “guidance level”. Ingestion: In the context of this document, the incorporation of a radionuclide into the body through the gastrointestinal tract. Intake: The activity of a radionuclide taken into the body (by ingestion, inhalation or through the skin) in a given time period or as a result of a given event. Internal exposure: In the context of this document, a radiation exposure resulting from radioactive material that gets inside the body by ingestion, inhalation or through the skin. Radioactive materials produce radiation exposure during the entire time they are inside the body until the material is no longer radioactive (it decays) or it is naturally removed by the body e.g. by urinary or faecal excretion. See also “exposure”. XVI . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ionizing radiation: Radiation that has a high enough energy to remove electrons from atoms and is therefore capable of producing ion pairs in a material/tissue. Examples are alpha particles, beta particles and gamma rays. Mineral water: Water obtained directly from natural or drilled sources from underground water. In order to be characterized as natural mineral water, the water needs to meet a number of criteria as defined by Codex Standard 108–19811. Natural background radiation: Amount of radiation to which a population is exposed from natural sources, such as terrestrial radiation resulting from naturally occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally occurring radionuclides deposited in the human body. Non-emergency situations: In the context of this document, a situation where a planned activity results in a radiation exposure from a source (e.g. radioactive discharges from the normal operation of a nuclear medicine facility or a nuclear power plant) or where an existing exposure already exists when a decision on the need for control needs to be taken (e.g. exposure to natural background radiation and exposure to residual radioactive material from a previous nuclear or radiological emergency after the emergency has been declared ended). Nuclear emergency: An emergency in which there is, or is perceived to be, a hazard due to radiation exposure in a situation involving atomic fission or fusion. Fission and fusion are associated with the generation of electrical power by nuclear power plants, scientific research and nuclear weapons test/use. See also “emergency situation”. Parametric value: In the context of the Euratom Drinking-Water Directive2, the value of radioactive substances in water intended for human consumption above which Member States shall assess whether the presence of such radioactive substances poses a risk to human health which requires action and, where necessary, shall take remedial action to improve the quality of water to a level which complies with the requirements for the protection of human health from a radiation protection point of view. Radiation: Energy that travels through matter. In the context of this document this term is used to refer to ionizing radiation. See also “ionizing radiation”. Radioactive decay: The process of spontaneous transformation of the nucleus of unstable atoms resulting in the release of radiation in the form of alpha particles, beta particles, gamma rays and other particles. See also “atoms”, “radiation”, “alpha particles”, “beta particles” and “gamma rays”. Radioactive material: A substance that contains unstable atoms that give off radiation as they decay. See also “radioactive decay”. Radioactivity (also called "activity"): The property of the nucleus of unstable atoms that causes them to spontaneously release energy in the form of photons (e.g. gamma rays) or subatomic particles (e.g. alpha or beta particles). The amount of radioactivity is defined as the mean number of decays per unit time. See also “becquerel”. Radiological emergency: An emergency in which there is, or is perceived to be, a hazard due to radiation exposure from radiological devices or radioactive materials used in medical, industrial or research applications. See also “emergency situation”. Radionuclide: Radioactive species of an atom characterized by an unstable nucleus which spontaneously transforms, releasing energy in the form of radiation. 1 http://www.fao.org/input/download/standards/223/CXS_108e.pdf 2 http://ec.europa.eu/environment/water/water-drink/legislation_en.html . XVIIMANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Reference level: In the context of the system of radiological protection, a level of radiation dose above which it is not appropriate to plan to allow exposures to occur and below which optimization of protection and safety would continue to be implemented. Remedial action: See “remediation”. Remediation: In the context of this document, any measures carried out to reduce radiation exposure, through actions applied to the contamination itself (the source) or to the exposure pathways to humans. Risk: The likelihood of an event occurring that exposes populations to a hazard, combined with the severity of its consequences. In the context of this document, the term is used to refer to health risks associated with radiation exposure through drinking-water. Screening level: In the context of this document, these are levels of radioactivity in drinking-water, expressed as total alpha and total beta activity concentrations, below which no further action is required. Water safety plan: A comprehensive risk assessment and risk management approach to ensure drinking-water safety that encompasses all steps in the water supply, from catchment to consumer. XVIII . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER NON- EMERGENCY SITUATIONS Chapter 1 CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.1 BACKGROUND 1.1.1 Are radionuclides in drinking-water likely to be a public health risk in non-emergency situations No. The health risks associated with the presence of radionuclides in drinking-water are generally very low compared to those from microorganisms and chemicals. Any health effects from radionuclides in drinking- water will not be acute or immediate. Except in unusual circumstances, the radiation dose resulting from the ingestion of radionuclides in drinking-water is much lower than that received from other sources of radiation (see Information Box 1.1). Further, the levels of potassium-40 (40K) do not need to be considered in assessing health risks from radionuclides in drinking-water because potassium is a key element in regulating many body functions and the potassium content of the body (and 40K) is kept constant by a range of physiological processes. Information Box 1.1: Radiation doses from natural sources of radiation People typically receive a radiation dose of about 0.3 mSv each year due to radionuclides of natural origin in their diet; of this about 0.01 mSv (about 5%) comes from drinking-water. A dose of 0.3 mSv is typically 10% of the average annual radiation dose from all natural sources of radiation (cosmic rays, soil, radon, diet) received by an individual, which is about 2.4 mSv (UNSCEAR, 2008). ? 2 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.1.2 What are the possible sources of radionuclides in drinking-water in non-emergency situations Radionuclides in drinking-water can arise from natural or human-made (i.e. anthropogenic) sources. Many radionuclides occur in nature, including in rocks and soil, and concentrations of radionuclides in drinking- water are therefore more commonly detected in supplies derived from groundwater sources (IAEA, 2016). Of particular significance for human radiation exposure from drinking-water are the naturally occurring radionuclides that originate from the elements of the thorium and uranium decay series, for example radium-226, radium-228, polonium-210, lead-210 and radon. These radionuclides can arise in water from natural processes in the ground or human activities involving naturally occurring radioactive materials, such as uranium mining and other extractive industries (coal, oil and gas), the fertilizer (phosphate) industry and the building industry. Information Boxes 1.2 and 1.3 provide examples of activity concentrations of naturally occurring radionuclides in drinking-water across the world and an example from Germany showing the contribution they make to radiation exposure from natural background. Radon is considered separately within this guidance in Section 1.63. Human-made radionuclides may be present in drinking-water from several sources, such as accidental or regular discharges from nuclear facilities, discharges of radionuclides produced for and used in medicine or industry, discharges from military activities and global dispersion of nuclear weapons fallout. The human-made radionuclides that might be found in drinking-water are caesium-134, caesium-137, strontium-90, iodine-131, tritium and carbon-14. The levels of these radionuclides in drinking-water are generally very low and are usually not measurable using standard analytical methods, i.e. they are below the limits of detection (see Information Box 1.4). Information Box 1.2: Worldwide activity concentrations of naturally occurring radionuclides in drinking-water Data from across the world on levels of naturally occurring radionuclides in drinking-water have been reviewed (UNSCEAR, 2000; 2008; 2016). The activity concentrations of natural radionuclides can vary widely across a country dependent on the underlying geology. For example, average uranium levels in water sources worldwide used for public water supplies show great variability, notably for groundwater, where activity concentrations range from 0.00001 Bq L-1–200 Bq L-1. However, few drinking-water samples (generally < 3%) exceed the national or international guidelines for uranium (UNSCEAR, 2016). Worldwide typical values of naturally occurring radionuclides in drinking- water derived from the most widely available and representative data compiled by UNSCEAR (UNSCEAR, 2000) indicate that the activity concentrations of naturally occurring radionuclides in drinking-water are typically very low. Typical activity concentrations in drinking-water, Bq L-1 210Pb 210Po 226Ra 228Ra 228Th 230Th 232Th 235U 238U 0.01 0.005 0.0005 0.0005 0.00005 0.0001 0.00005 0.00004 0.001 Key: lead-210 (210Pb), polonium-210 (210Po), radium-226 (226Ra), radium-228 (228Ra), thorium-228 (228Th), thorium-230 (230Th), thorium-232 (232Th), uranium-235 (235U) and uranium-238 (238U). 3 Where radon remains dissolved in drinking-water, the radionuclides lead-210 or polonium-210 (radon decay products) may become important contributors to the overall dose from the ingestion of drinking-water. ? . 3MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Information Box 1.3: Contribution of naturally occurring radionuclides in drinking-water to annual natural background radiation exposure in Germany As part of systematic studies in Germany to obtain representative data on public exposure to radiation from natural radionuclides in German drinking-water (BfS, 2009), 582 samples from public water supplies were analysed between 2003 and 2008. These covered urban areas as well as regions known for elevated concentrations of naturally occurring radionuclides (mainly areas rich in granite and/or gneiss, e.g. Erzgebirge, Bayerischer Wald). The results showed that natural radionuclides in German drinking-water only contribute to a minor extent to the total mean value of annual natural background radiation exposure (2.1 mSv). The mean values of radiation exposure from drinking-water (ingestion dose) obtained from the data were about 0.009 mSv y-1 for adults and about 0.05 mSv y-1 for infants, assuming an annual ingested volume of drinking-water of 350 litres for adults and 55 litres for infants according to the German Radiation Protection Ordinance (BMU, 2001). However, there is a considerable range in variation of activity concentrations for uranium-238, uranium-234, radium-226, radium-228, radon-222, lead-210 and polonium-210. Information Box 1.4: Occurrence of anthropogenic radionuclides in drinking-water National experiences have shown that the vast majority of measurements of human-made individual radionuclides, such as caesium-137 and strontium-90, made as part of monitoring programmes in drinking-water sources around nuclear licensed sites are all usually below limits of detection (e.g. Environment Agency et al., 2016; Canada Nuclear Safety Commission, 2016; BMU, 1986; BMU, 2006). 1.1.3 How do naturally occurring radionuclides enter into drinking-water All materials in the earth’s crust contain naturally occurring radionuclides, mainly from the uranium and thorium decay series as well as potassium-40. These radionuclides, which are dispersed throughout rocks and soils normally in low concentrations, may leach into groundwater (see Information Box 1.5). They are, therefore, more commonly found in drinking-water derived from groundwater sources and springs than surface water and rainfall. Information Box 1.5: Behaviour of naturally occurring radionuclides in drinking-water The hydro-chemical behaviour of uranium, thorium and individual members of the uranium and thorium decay series is complex and depends to a great extent on a range of other water quality parameters such as alkalinity, pH, redox and chemical composition. For example, thorium is considered to be relatively immobile and insoluble in the vast majority of natural waters while uranium can be highly mobile especially in water where the pH is near neutral and has high carbonate alkalinity. ? 4 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.1.4 When should radionuclides in drinking-water be considered in non-emergency situations The potential for radionuclides to be present in drinking-water should be considered when a significant source of radionuclides entering drinking-water supplies is expected. This should be anticipated where there are areas with high levels of naturally occurring radionuclides in the underlying rocks and soil. Activities involving naturally occurring radioactive materials, such as uranium mining and other extractive industries, and the use of human-made radionuclides in industry and medicine may also lead to radionuclides being present in drinking-water (See Question 1.1.2). There are circumstances, for example some deeper groundwater sources in certain regions, where the health risks from naturally occurring radionuclides may be greater than those from chemicals. ? . 5MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.2 PURPOSE AND SCOPE OF THE GUIDELINES FOR DRINKING-WATER QUALITY 1.2.1 What is the purpose of the Guidelines for drinking-water quality The primary purpose of the Guidelines for drinking-water quality (GDWQ) is to protect public health. The GDWQ detail the World Health Organization (WHO) recommendations for managing the health risks from hazards that may compromise the safety of drinking-water, including radionuclides. The recommendations should be considered in the context of managing the risk from other sources of exposure to these hazards, such as air and food. The GDWQ provide a comprehensive approach to assess and manage risks to drinking-water safety. This holistic approach, the framework for safe drinking-water shown in Figure 1.1, encompasses the development of health-based targets (parameters and associated “limits” in national drinking-water standards), the assessment and management of risks by water suppliers (water safety plans) and independent surveillance to ensure that water safety plans are being implemented effectively and that health-based targets are being met. The water safety plan approach to risk assessment and risk management of drinking-water supplies increases confidence in the safety of the drinking-water by ensuring that the most significant risks are addressed and limited resources are used the most effectively. Chapter 9 of the GDWQ provides specific supporting information on the radiological aspects of drinking-water quality, as shown in Figure 1.1. The assessment and management of health risks from radionuclides need to be considered in the context of other potential health risks from the water supply, namely microbial and chemical risks 4, the availability of other water supplies and available resources. The GDWQ are addressed primarily to water and health regulators, policy-makers and their advisers, to assist in the development of national standards. 4 Chapter 8 of the GDWQ provides specific information on the chemical aspects of uranium in drinking-water. ? 6 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Figure 1.1. Interrelationships among the individual chapters of the Guidelines for drinking-water quality in ensuring drinking-water safety Introduction (Chapter 1) A conceptual framework for Implementing the Guidelines (Chapter 2) FRAMEWORK FOR SAFE DRINKING-WATER SUPPORTING INFORMATION Microbial aspects (Chapters 7 and 11) Chemicals aspects (Chapters 8 and 12) Radiological aspects (Chapter 9) Acceptability aspects (Chapter 10) Application of the Guidelines in specific circumstances (Chapter 6) Climate change, Emergencies, Rainwater harvesting, Desalination systems, Travellers, Planes and ships, etc. Health-based targets (Chapter 3) Surveillance (Chapter 5) Water safety plans (Chapter 4) Public health context and health outcome System assessment Monitoring Management and communication 1.2.2 What guidance does WHO provide on radionuclides in drinking-water The GDWQ provide guidance on drinking-water quality, including radiological aspects (see Question 1.2.1). Chapter 9 of the GDWQ provides specific information for assessing and managing health risks from radionuclides in drinking-water. • Criteria (screening levels and guidance levels; see Question 1.3.1 for more information) are provided which allow for the assessment of the quality of drinking-water with respect to its radionuclide content. ? . 7MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S • A methodology is given for interpreting the health criteria to support the assessment and management of health risks from radionuclides in drinking-water, which includes: – the identification of the individual radionuclides potentially present – measurement of the radionuclide concentrations in drinking-water – evaluation of potential radiation doses that could be received. • Guidance is provided on remedial actions that can be taken to decrease radionuclide concentrations in drinking-water. • Guidance is provided on radon in drinking-water supplies and the health risks arising from radon in drinking-water. 1.2.3 What situations can the GDWQ be used for The guidance on radionuclides in the GDWQ is primarily for non-emergency situations where there could be ingestion of drinking-water containing radionuclides over extended periods of time, leading to prolonged radiation exposure of individuals. Exposure could continue for many years or even over a lifetime. The criteria in the GDWQ for radionuclides are not applicable during radiological and nuclear emergencies. For emergency situations, criteria for taking emergency response actions including those related to drinking-water are issued in other international standards, that is the International Atomic Energy Agency (IAEA) Safety Standard Series (IAEA, 2011; 2015), for which WHO is a sponsoring organization (see Question 2.1.4). However, there is information in the GDWQ on general planning and management of drinking-water quality in emergencies that might be useful in a nuclear or radiological emergency (see for example Sections 4.4.3 and 6.7 in the GDWQ). Other information in the GDWQ on analytical methods, remedial measures and the effectiveness of water treatment may also be useful in the event of a radiological or nuclear emergency. 1.2.4 Are the radiological criteria in the GDWQ mandatory No. The GDWQ is international guidance designed to help countries develop customized regulations and standards. Countries should consider their specific situation when adopting the GDWQ, including the criteria to use (i.e. whether to adopt the individual dose criterion (IDC), screening levels and guidance levels without change). Question 1.5.10 covers the considerations for developing national standards. ? ? 8 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.2.5 Why do the criteria provided in the GDWQ not apply during a radiological or nuclear emergency The criteria for radiological aspects in the GDWQ5 (i.e. individual dose criterion (IDC), screening levels and guidance levels) do not apply to emergency situations because they have been established for the ingestion of drinking-water over prolonged periods of time (e.g. for many years or even over a lifetime), which is not appropriate for emergency situations. In the latter, exposures from drinking-water usually only occur in the short term, although possibly from higher activity concentrations of radionuclides in drinking-water than would typically be found in non-emergency situations. The dose criteria for use in an emergency situation can therefore be higher than the IDC in the GDWQ and the International Basic Safety Standards (BSS) reference level for drinking-water for non-emergency situations. International standards and criteria that apply for drinking-water quality in emergency situations are described in Section 2, for example Question 2.1.4. Once the relevant authorities have declared the termination of an emergency, any remaining radionuclides in drinking- water over the longer term should be treated as a non-emergency situation and the GDWQ criteria should be used. 1.2.6 Are there any international criteria for radionuclides in bottled and packaged drinking-water The Codex Alimentarius Commission has published a Codex General Standard for bottled/packaged drinking- water (other than natural mineral waters), CODEX STAN 227-2001 (CODEX, 2001). This standard states that the water should comply with the health-related requirements of the GDWQ for microbiological, chemical and radiological substances. There is also a Codex Standard for natural mineral waters, CODEX STAN 108-1981 (CODEX, 1981), but this standard does not contain any criteria for radionuclides. For emergency situations, the international guidance in IAEA Safety Standards Series on preparedness and response for a nuclear or radiological emergency, which includes General Safety Requirements No. GSR Part 7 (IAEA, 2015) and General Safety Guide No. GSG-2 on Criteria for use in preparedness and response for a nuclear or radiological emergency (IAEA, 2011) apply to drinking-water in a nuclear or radiological emergency irrespective of whether the drinking-water is packaged or not. These standards are applicable for drinking-water destined for human consumption in affected countries (see Section 2, Question 2.1.4). 5 Some of the information in Chapter 9 of the GDWQ is applicable during emergency situations, although the criteria included in that chapter (IDC, screening levels and guidance levels) are not applicable to emergencies. Further useful general information on planning for emergencies is given in Sections 4.4.3 and 6.7. ? ? . 9MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S 1.2.7 Should naturally occurring radionuclides and human-made radionuclides present in drinking-water be managed differently No. A radiation dose associated with the intake of a radionuclide into the body from drinking- water does not depend on its source. Accordingly, the GDWQ do not differentiate between radionuclides that occur naturally and those that arise from human activities in terms of the criteria included to assess health risks. However, in terms of risk management, there is a difference because human-made (i.e. anthropogenic) radionuclides are often controllable at the point at which they enter the water supply. Naturally occurring radionuclides, in contrast, which usually enter the water supply from the surrounding rocks and soil, are often less amenable to control. This may influence the actions that are taken in the event that the criteria in the GDWQ are exceeded. ? 10 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.3 APPROACH ADOPTED BY WHO FOR ASSESSING THE PUBLIC HEALTH RISK FROM RADIONUCLIDES IN DRINKING-WATER 1.3.1 What are the criteria used in the GDWQ for assessing health risks from radionuclides in drinking-water The criteria in the GDWQ for assessing health risks from radionuclides in drinking-water are screening levels, guidance levels and an individual dose criterion (IDC). Radon is not included in these criteria and is considered separately, see Section 1.6. Each criterion is discussed in more detail in other questions, as indicated below. • The GDWQ include an IDC of 0.1 mSv y-1 for assessing health risks to an individual from prolonged exposure to radionuclides in drinking-water. The IDC provides the basis for the development of the operational criteria that can be measured by water suppliers and regulators (i.e. screening levels and guidance levels). • The screening levels are total activity concentrations that can be measured as part of drinking-water monitoring to assess if the IDC may be or is exceeded. The screening levels are 0.5 Bq L-1 for gross alpha activity and 1 Bq L-1 for gross beta activity (see Question 1.3.3). If either of the screening levels is exceeded, the activity concentrations of individual radionuclides should be determined and compared with the guidance levels in order to determine if the IDC is exceeded (see below). ? . 11MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER • The guidance levels are specific for individual radionuclides and are the concentration that, if present in the drinking- water consumed throughout a year at a rate of 2 litres per day, would result in an individual dose of 0.1 mSv being received (see Question 1.3.4). Question 1.5.6 explains how to use the guidance levels to determine if the IDC is exceeded for one or several radionuclides present in drinking-water). National experiences have shown that the vast majority of drinking-water supplies comply with the radiological criteria in the GDWQ. 1.3.2 What is the individual dose criterion of 0.1 mSv y-1 The individual dose criterion (IDC) is a criterion in the GDWQ for assessing health risks from prolonged exposure to radionuclides in drinking-water. The IDC of 0.1 mSv y-1 represents a very low level of health risk (see Information Box 1.6). The IDC of 0.1 mSv is for consumption of drinking-water over the course of a year regardless of whether the radionuclides are naturally occurring or human-made. In practice, the IDC is translated in the GDWQ into two operational quantities, screening levels and guidance levels (see Questions 1.3.3 and 1.3.4). Information Box 1.6: Interpretation of the IDC The individual dose criterion (IDC) should not be interpreted as a limit above which drinking-water is unsafe for consumption. Drinking-water is a fundamental requirement of life and the risks of not having a drinking-water supply are likely to be much higher than consuming drinking-water that does not meet the IDC. 1.3.3 What purpose do the screening levels serve and how should they be used The screening levels are operational criteria, expressed as total alpha and beta activity concentrations, below which no further action is required. This is because the individual dose criterion (IDC) of 0.1 mSv y-1 would usually not be exceeded. Screening levels enable water suppliers and regulators to assess the total radioactivity in drinking-water in a resource- and cost-efficient manner. The use of screening levels is recommended because the process of identifying individual radionuclides in drinking-water and determining their concentration is time-consuming, resource intensive and expensive; and further, in most situations activity concentrations in drinking-water are very low and detailed analysis is not normally justified for routine monitoring. The screening levels are 0.5 Bq L-1 for gross alpha activity and 1 Bq L-1 for gross beta activity. They are robust values that have been derived to cover the most common radionuclides that would be found in drinking-water and their contributions to the radiation dose from the consumption of drinking-water. These screening measurements do not provide the identity ? ? 12 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER of specific radionuclides. Information Box 1.7 discusses what countries should do if they have a national dose criterion different from the IDC of 0.1 mSv y-1 and want to set screening levels. If either screening level is exceeded, further investigation should be triggered (see Question 1.5.3). The stepwise process for applying the screening (and guidance) levels is shown in Figure 1.2 in Question 1.5.3. In using the screening levels, it is important to be aware of the following situations. • The methods for gross alpha and gross beta measurements rely on the detection of emitted alpha or beta particles during the radioactive decay of the radionuclides. They are appropriate for most situations in which radionuclides in drinking-water are likely to be found. • However, there are a few radionuclides that cannot be measured using these screening methods. Question 1.4.3 provides further information on this and the approach to be adopted if the local situation indicates that these radionuclides may be present. • There are a few naturally occurring radionuclides (notably radium-228 and polonium-210) where the IDC of 0.1 mSv y-1 could be exceeded, even if the screening levels are not exceeded, in the uncommon situation where these radionuclides are the only significant contributors to the total gross activity concentration. If the local geology and hydrology indicate that these radionuclides may be present, the individual radionuclides should be measured and compared with the guidance levels (see Question 1.5.6). Information Box 1.7: Establishing screening levels based on national dose criterion that is different from the IDC If a country has established a national dose criterion that is different to the IDC of 0.1 mSv y-1 and is using gross alpha and gross beta measurements as a screening approach, different screening levels need to be determined, taking into account the radionuclides in the drinking-water and their contributions to the dose; specialist advice should be sought. 1.3.4 What purpose do the guidance levels for radionuclides serve and how should they be used The guidance level for a radionuclide is the concentration that, if present in the drinking-water consumed throughout the year at a rate of 2 litres per day, would result in an individual dose of 0.1 mSv. If several radionuclides have been identified, then a sum across the radionuclides present needs to be made to check that together they do not lead to the 0.1 mSv y-1 individual dose criterion (IDC) being exceeded. It is likely that drinking- water from a groundwater source containing naturally occurring radionuclides will contain several radionuclides in varying amounts. Further details of assessing if the IDC has been exceeded and summing across radionuclides are given in Question 1.5.6. Guidance levels are provided in the GDWQ for a comprehensive set of naturally occurring radionuclides most commonly detected in drinking-water supplies as well as for human-made radionuclides potentially relevant for non-emergency ? . 13MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S situations. The guidance levels for the radionuclides most likely to be identified in drinking-water are given in Table 9.2 in the GDWQ and summarized in Table 1.1 of this document. For other radionuclides, values can be found in Table A6.1 of the GDWQ. The guidance levels are rounded to the nearest order of magnitude to reflect the generic nature of the assumptions made in the calculation of the guidance levels, these being conservative for the majority of cases. The guidance levels should be used as a trigger for further investigation and not be interpreted as a limit above which drinking-water is unsafe for consumption. The guidance levels are likely to be conservative because they assume that drinking-water is consumed at this activity concentration for the whole year at a rate of 2 litres per day. In practice, activity concentrations often vary throughout the year and the consumption of drinking-water may be from a number of different sources (e.g. at home, a workplace, school, public places, etc.). A guidance level can be calculated for a specific situation, for example using local or regional drinking-water consumption rates, as explained in Chapter 9 of the GDWQ. Annex 1 provides further information on the calculation of guidance levels, including calculations for children. If a guidance level is exceeded, due to the conservative assumptions made in calculating the guidance levels, it is very important to investigate whether the sample taken is representative of the situation at other times of the year and to understand the drinking-water habits of the population. Question 1.5.9 gives further details of what should be done if a guidance level is exceeded. The guidance levels in the GDWQ do not apply in emergency situations (see Question 1.2.5). 1.3.5 Do the guidance levels need to be adjusted for children No. As the guidance levels are not limits above which drinking-water is unsafe for consumption but are used as triggers for further investigation, it is appropriate for them to be based on parameter values for adults. The assumptions made in the calculation of the guidance levels are conservative, reflecting the assessment methodology adopted in the GDWQ. If a guidance level is exceeded, it is important that there is further investigation; this may include a site-specific assessment for the population affected and can take into account their drinking-water consumption habits. In the case of there being a prolonged period over which a guidance level is exceeded, an assessment of doses to children and babies drinking bottled milk reconstituted with drinking-water may be appropriate. This is because children are more sensitive to exposure from some radionuclides (as reflected in different dose coefficients), although they typically consume smaller quantities of drinking-water than adults (for further details, see Question 1.5.9). ? 14 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.3.6 What is the reference level (1 mSv y-1) and how does it relate to the individual dose criterion (0.1 mSv y-1) for drinking-water The International Basic Safety Standards (BSS6) (IAEA, 2014) recommend a reference level for the radiation dose due to consumption of drinking-water of approximately 1 mSv y-1. A reference level represents the level of dose or risk above which it is judged to be inappropriate to plan to allow exposures to occur and below which the optimization of protective actions should be planned in order to keep doses as low as reasonably achievable (ALARA). It should not be regarded as an acceptable dose or as a dose limit, and efforts should be made to reduce any exposures that are above the reference level, to a level that is below, if possible. The International BSS require regulatory authorities to establish reference levels for radiation dose due to radioactivity in drinking-water, an approach that is consistent with the GDWQ. The individual dose criterion (IDC) of 0.1 mSv y-1 represents a very low level of health risk. The majority of water supplies comply with this criterion and establishing a national standard at 0.1 mSv y-1 is appropriate for most countries as part of the optimization process (ALARA). However, in cases where this is not achievable, regulatory authorities may establish a specific reference level (or national standard) for radionuclides in drinking-water higher than 0.1 mSv y-1 (IDC), but generally less than the International BSS reference level of 1 mSv y-1, depending on the circumstance (see Question 1.5.10). Situations may arise where it may be appropriate to permit doses higher than 1 mSv y-1 for selected population groups, depending on the situation at the time, and considering a balance of the overall risks, including the risk of not having a supply of drinking-water. The consequence of this would be the acceptance of a potential slight increase in radiological risks to health. 6 The International BSS are the international benchmark for radiation safety. Eight organizations sponsor the International BSS: the European Commission, Food and Agricultural Organization of the United Nations (FAO), IAEA, International Labour Organization (ILO), Organisation for Economic Co-operation and Development/Nuclear Energy Agency (OECD/NEA), Pan American Health Organization (PAHO), United Nations Environment Programme (UNEP) and WHO. The International BSS are used in many countries as the basis for national legislation to protect workers, patients, the public and the environment from the risks of ionizing radiation; they are not legally binding. ? . 15MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.4 MEASURING RADIONUCLIDES IN DRINKING-WATER 1.4.1 At what points in the water supply chain should measurements of radionuclides in drinking-water be made It is important that the measurements that are made are representative of the drinking-water being consumed. If water is treated before consumption, the water should be monitored after treatment because treatment can reduce the activity concentrations of many radionuclides. Further information on the likely effectiveness of water treatment is given in Question 3.2. In general, the concentration of radionuclides does not change in the distribution system (except for radon; see Section 1.6), so it is appropriate to measure the water at the treatment works after treatment or at storage reservoirs prior to distribution. For supplies of drinking-water that are not treated, e.g. some small water supplies, the radionuclides can be measured at the source or the point of collection. Ideally, some measurements should be made at the point of consumption, i.e. at the tap or communal point of collection; however, this is usually not practicable. For a new drinking-water supply, measurements of radionuclides in the water should be made at the source as part of characterizing it and determining its suitability as a source of drinking-water (see Question 1.4.2 for more information). The extent of treatment that will be carried out should also be taken into account (see Question 3.2). This characterization should be carried out along with assessing microbiological and chemical risks as part of developing water safety plans. ? 16 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.4.2 With what frequency should measurements of radionuclides in drinking-water be made The frequency for measuring activity concentrations of radionuclides in drinking-water should be set taking into account the potential for there to be a public health risk from radionuclides in the drinking-water, the available resources and other priorities for providing safe drinking-water, including the analyses of microbiological and chemical contaminants. In general, new water supplies should be sampled and analysed for radionuclides to determine their suitability for drinking-water before design and construction. It is important that the seasonal variation in radionuclide concentrations are characterized over the first year with the water tested frequently enough to show any seasonal variation, typically at least four times over the year (i.e. once per season). Ideally, measurements of individual radionuclides should be made in addition to measurements of gross alpha and gross beta activity, particularly if the presence of naturally occurring radionuclides is expected. Due to the possibility of high heterogeneity in radionuclide levels in groundwater, it may be necessary to consider monitoring of new drinking-water supplies (including new abstraction points); this should be done even if there is already information on the groundwater source, or similar groundwater sources in the area and knowledge about the underlying geology (that could lead to high levels of uranium and/or thorium in rocks and the ground). The sampling frequency of existing water supplies should be linked to several factors: the level of activity concentrations in the water; the source of the supply (i.e. surface water or groundwater) and how likely it is that activity concentrations may vary across the year (e.g. groundwater sources may display less variability than surface water sources); the size of the population supplied; and the quantity and quality of historical monitoring records. In determining the frequency, the following points should also be considered. • If activity concentrations are below screening levels and stable, the frequency of monitoring can be reduced in agreement with the relevant regulatory agencies and health and water authorities to once every two to five years (or longer), depending on the water source. • If gross activity concentrations are approaching the screening levels, activity concentrations of individual radionuclides are approaching the guidance levels or, where multiple radionuclides are measured, the sum of the ratios of the observed concentrations of the individual radionuclides to their guidance levels approaches unity (see Question 1.5.6), sampling frequency should be maintained, or even increased. • Increasing the sampling frequency in the following situations: a. if the measurements indicate that there is an increasing trend in the activity concentrations; b. in areas with residual radioactive material from past practices that were never subject to regulatory control; c. in areas where there are residual levels of radionuclides following a nuclear or radiological emergency; d. if sources of potential radionuclide contamination exist nearby or are expected to change rapidly with time (e.g. mining activity or nuclear reactors). • If activity concentrations consistently exceed the screening levels, then further investigation is needed, including further measurements and a possible increase in sampling frequency (see Question 1.5.3). An international standard is available on the design of sampling programmes (ISO, 2006). Some examples of drinking- water monitoring programmes are given in Information Box 1.8. ? . 17MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Information Box 1.8: Examples of drinking-water monitoring programmes Germany The drinking-water ordinance in Germany (BMG, 2016) contains requirements on monitoring of drinking-water for radionuclides. Initial analysis is required to identify and assess the annual average activity concentrations in public water supplies and comprises • for existing drinking-water supplies: four analyses in four different quarters within four years; • for newly-established drinking-water supplies: four analyses in four different quarters within one year; • regular analyses are necessary if the initial analyses reveal an exceedance of one or more parametric values1 for radioactive substances. Japan After the Fukushima Daiichi nuclear power plant accident in March 2011 in Japan, monitoring of drinking-water for caesium-134 (134Cs) and caesium-137 (137Cs) was carried out and has continued beyond the initial emergency phase of the accident because radioactive caesium was detected in tap water (MHLW, 2011). The recommended monitoring frequency has progressively been reduced from at least daily, to weekly during the emergency phase, and then to at least monthly in April 2012, when the measurement frequency was recommended to be more than once a month for 134Cs and 137Cs (MHLW, 2012a; 2012b). However, there are several water utilities still measuring radioactive caesium more frequently (as of January 2018) for added reassurance to ensure radiation in drinking- water remains at safe levels. United States of America In the United States of America, suppliers providing drinking-water to at least 15 service connections or to more than 25 individuals (who consume it for a year) must conduct initial monitoring consisting of quarterly samples over the first year at each entry point to the distribution system after beginning operation, or after beginning to use a new source of water supply. The initial results determine the frequency of future monitoring: 1. if the initial monitoring results are less than the defined detection limit, then monitoring frequency is reduced to one sample every nine years; 2. if the initial monitoring results are greater than the defined detection limit but less than half of the maximum contaminant limit, then monitoring frequency is reduced to one sample every six years; 3. if the initial monitoring results are greater than half of the maximum contaminant limit but less than the maximum contaminant limit, then monitoring frequency is reduced to one sample every three years; and 4. if the initial monitoring results are greater than the maximum contaminant limit, then quarterly samples are required. Different monitoring frequencies may be established for different contaminants for the same supply, based on the results for that one supply compared to each of four maximum contaminant levels, e.g. one system may be required to sample for gross alpha activity every three years, and uranium every six years, depending on the sample results for gross alpha activity and uranium, respectively. Source: EPA (2000). 1 Parametric value for radioactive substances is the term used in the Euratom Drinking-Water Directive (EC, 2013); values equivalent to the screening levels and guidance levels in the GDWQ are given. 18 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 1.8: Examples of drinking-water monitoring programmes (continued) Jordan In Jordan, regular monitoring of radionuclide levels in water at various points of the supply chain between wells and consumer taps are made within the Disi Water Conveyance Project (see case study in Section 4.3 for additional information). The water provider and the health authorities follow a monitoring protocol that entails the following frequencies at each of the agreed upon sampling points. 1. Quarterly grab samples for each of the 55 wells in the Disi Water Conveyance Project well field to assess trends of radionuclide concentrations with time; frequency is reduced to once per year after two years of operation. 2. Monthly grab sample from the combined water of the 55 wells at the header tank in the south of Jordan before the water is admitted to the main 320 km long conveyer pipe. 3. Monthly composite samples for the Disi water before blending at the two delivery points in Amman. 4. Yearly monitoring of the waters containing low activity concentrations used for blending (water taken from Zara- Ma’en and Zai treatment plants whose historical results for gross alpha, gross beta, radium-226 and radium-228, are consistently below the analytical detection limits). 5. Monthly composite samples for the drinking-water after blending, measured at the outlets of the main reservoirs in Amman. 6. Monthly composite samples from public reservoirs to represent the water supplied to consumers in the different distribution zones in Amman. 1.4.3 Are there any radionuclides that are not detected by standard gross alpha and gross beta screening methods Gross alpha measurement will detect all the alpha-emitting radionuclides that are likely to be found in drinking-water. Standard gross beta measurement will detect most other radionuclides that emit beta particles that could be found in drinking-water under non-emergency situations. However, there are a few radionuclides that will not be detected by standard gross beta measurement methods or where their concentrations will be underestimated because either they do not emit beta particles or the energy of the beta particle emission is too low to be efficiently detected by the method. The notable radionuclides that are not detected by gross beta measurement methods are tritium, carbon-14 and sulfur-35 (Information Box 1.9 provides an example of the monitoring requirements for tritium in Europe). Some gaseous or volatile radionuclides, such as isotopes of iodine will also not be detected, as losses of the radionuclides will occur during the analytical procedure. However, routine analysis for these human-made radionuclides is unlikely to be necessary in most situations. The notable radionuclides for which activity concentrations are likely to be underestimated are naturally occurring lead-210 and radium-228 (228Ra). Due to the low energy of their beta particle emissions, the efficiency of their detection ? . 19MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S is very poor and accordingly, their contribution to the gross beta activity is underestimated. An example is discussed in Information Box 1.10. In the uncommon situation where these radionuclides are the most significant contributors to the total gross activity concentration, this may lead to the individual dose criterion (IDC) of 0.1 mSv y-1 being exceeded even if the screening levels are not. If it is thought that these radionuclides may be present, radionuclide-specific analyses should be made. A review of the geology and hydrology of the area and radionuclide content of rocks, mineralization and soil, as well as historical data can be used to determine the extent of these naturally occurring radionuclides in groundwater. Information Box 1.9: Requirements for monitoring tritium in the Euratom Drinking-Water Directive In the Euratom Drinking-Water Directive1 (EC, 2013), Member States are required to monitor tritium in water intended for human consumption where a human-made source of tritium or other radionuclide is present within the catchment area and it cannot be shown on the basis of other surveillance programmes or investigations that the level of tritium is below the parametric value of 100 Bq L-1. If the concentration of tritium exceeds its parametric value, an investigation of the presence of other human-made radionuclides is required (EC, 2013). 1 The European Commission (EC) has specific responsibilities in monitoring the implementation of the European Union law on radioactivity in drinking-water. The Euratom Drinking-Water Directive (EC, 2013) provides a framework for controlling radioactivity in drinking-water and the radiation dose received from the consumption of different forms of drinking-water (tap water and bottled water). The Directive does not apply to natural mineral waters and to small private supplies. Further information on measurement methods is covered in Section 3.5. The measurement of radon in drinking-water is covered in Section 1.6. Information Box 1.10: Monitoring of 228Ra in Jordan In Jordan, regular monitoring of radionuclide levels in water at various points of the supply chain between the wells and consumer taps are made within the Disi Water Conveyance Project. Analysis for radium isotopes and dose calculations are conducted since it is known that 228Ra is the dominant radionuclide present and since, as noted above in the main text, gross beta measurements may not adequately detect this radionuclide. In Jordan, there have been a number of measurements where the gross beta activity concentration is less than or about 1 Bq L-1 but the measured activity concentrations of 228Ra are higher than the guidance level of 0.2 Bq L-1 (unrounded value) and the dose is therefore > 0.1 mSv y-1 (using the GDWQ default assumptions on drinking-water consumption rates). 20 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.5 HOW TO APPLY THE GDWQ METHODOLOGY FOR RADIONUCLIDES IN DRINKING-WATER 1.5.1 If a screening level is exceeded for one or a few drinking-water samples, does this mean that the radiation dose will be greater than the individual dose criterion of 0.1 mSv y-1 No. An exceedance of either the gross alpha or the gross beta screening levels does not necessarily mean that the individual dose criterion (IDC) of 0.1 mSv y-1 will be exceeded. The IDC is an annual criterion and so if the gross activity screening levels are exceeded for a short time in an individual drinking-water sample or even a few samples, this does not necessarily imply that the IDC will be exceeded. If either of the screening levels is exceeded, then there is a need to investigate the situation further, e.g. take further samples (see Question 1.5.3). ? . 21MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.5.2 Is any action required if the screening levels are not exceeded If both the gross alpha and gross beta screening levels are not exceeded, routine monitoring of drinking-water should continue at the locations and frequency that has been agreed with the water quality regulator. The individual dose criterion (IDC) of 0.1 mSv in a year will not be exceeded in the vast majority of cases; however, there are two uncommon situations that are an exception to this. • The first is if it is suspected that the water may contain a radionuclide that will not be detected by the screening methods. Question 1.4.3 provides information on the main radionuclides, which are human made, that will not be detected by the gross alpha and gross beta screening methods. Other sources of information may indicate that radionuclides in drinking-water could be present but would not be detected e.g. other environmental monitoring data in the area and the catchment that the water is drawn from, knowledge of sites that could have led to discharges of radionuclides to the catchment and local geology. • The second is if the most significant contributors to the total activity concentration are radionuclides that are not detected efficiently by the screening methods. As explained in Question 1.4.3, radium-228 (228Ra) and polonium-210 (210Po) are the most notable. See Information Box 1.11 for examples of situations where 228Ra in drinking-water is the highest contributor to the dose. In these cases, radionuclide-specific measurements should be made and compared with the relevant guidance levels (see Question 1.5.3). Information Box 1.11: Examples where 228Ra is the most significant contributor to radionuclide concentrations in drinking-water Jordan: Disi well water measurements between October 2013 and May 2015 226Ra: 0.31–0.47 Bq L-1 228Ra: 1.07–1.41 Bq L-1 Lead-210 (210Pb): 0.02 Bq L-1 Concentrations have remained stable over time. Queensland, Australia: 110 bore holes reflecting a range of aquifer lithology (area of 1.7 million km2) (Kleinschmidt, Black & Akber, 2011) 226Ra: mean 0.07 Bq L-1 (0.01–0.96 Bq L-1) 228Ra: mean 0.14 Bq L-1 (0.01–2.8 Bq L-1) Uranium-238 (238U): mean 0.15 Bq L-1 (0.04–0.71 Bq L-1) ? 22 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.5.3 What further action is required if either of the screening levels is exceeded for a drinking-water sample If the gross beta screening level is exceeded, the contribution from potassium-40 should be subtracted from the measurement(s) following a separate determination of the total potassium in the drinking-water (see Question 1.5.4). If either of the screening levels is exceeded (after subtracting the contribution from potassium-40 for gross beta measurements), the validity of the result should be confirmed by repeating the measurement. If some of the original drinking-water sample is left, a repeat measurement could be carried out. Once the initial measurement has been confirmed, the next step is to carry out further measurements of gross alpha and/or gross beta activity concentrations in the drinking-water. These are needed to assess the situation and whether it is varying with time. Initially, further samples should ideally be taken at least weekly for a few weeks. It is worth collecting enough sample volume so that individual radionuclide analysis can be carried out later, if necessary. If the measured gross activity concentrations continue to exceed the screening level(s), further samples should be taken over at least a period of a few months. This is needed to understand potential seasonal variations because activity concentrations averaged over an extended period may not exceed the screening level(s). Temporal variability of radionuclides may vary widely unless the water source is very stable and, in most cases, will match the characteristics of the catchment. Large variations may possibly also be seen due to discharges of radionuclides to surface water sources if these are not controlled or if unauthorized discharges occur. The duration of the monitoring period will depend on the characteristics of the water source and the results of the ongoing monitoring. If further measurements made over an agreed period following the initial measurement that exceeded the screening level, fall below the screening level, then no further intervention is required. Some occasional sampling might be needed in addition to the routine monitoring programme, e.g. at a greater frequency than normal, to provide reassurance that the low levels of radionuclides are being maintained. If screening level(s) are consistently exceeded, the radionuclides that are present in the water need to be identified. Radionuclide-specific analyses are required to both determine if a radionuclide is present and, if it is, what the activity concentration in the drinking-water is. Potential sources of radionuclides should be studied (see Question 1.5.5 for further information) and a specific analytical strategy developed. The process is illustrated schematically in Figure 1.2. ? . 23MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Figure 1.2. Flowchart for measurement of radionuclides in drinking-water No Determine gross alpha and gross beta activity. Is criterion for gross beta exceeded? Check validity of measurement(s) made. Look at relevant information on sources of radionuclides and develop analytical strategy. Perform radionuclide-specific analyses. Subtract potassium-40 from gross beta measurement. Is gross beta criterion still exceeded? Check measured concentrations against Guidance Levels and check if the IDC is exceeded using the summation method as described in Question 1.5.6. Is criterion for gross alpha exceeded? Collect further samples for a few months. [Collect enough samples for radionuclide analyses if it becomes necessary] After about 1 month, are screening levels still exceeded? Return to routine monitoring. Consider increased frequency for a few months for reassurance purposes. Return to routine monitoring. Return to routine monitoring. No No Yes Yes Yes Yes 24 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.5.4 What is the reason for subtracting the contribution of potassium-40 from gross beta activity when the gross beta activity concentration exceeds the screening level? How can it be performed Gross beta measurements will include a contribution from potassium-40 (40K), which is a beta emitter that occurs naturally in a fixed ratio to stable potassium. Potassium is a key element in regulating many body functions and the potassium content of the body is kept constant by physiological processes, so the content of 40K in the body is also regulated naturally and does not accumulate in the body whatever the size of the intake. The contribution of 40K to the measured gross beta activity concentration should therefore be subtracted if the gross beta screening level is exceeded. It is impractical to use a radionuclide measurement technique to determine the concentration of 40K in a drinking-water sample due to its low gamma-ray emission and the difficulty of chemically isolating the radionuclide from solution. Because of the fixed ratio between 40K and stable potassium, chemical analysis can be used to determine total potassium. The beta activity due to 40K can be calculated using a factor of 27.9 Bq per gram of total potassium. The formula is shown in Information Box 1.12. Information Box 1.12: Calculation of 40K in water 40K in water sample (Bq L-1) = total potassium in water sample (g L-1) × 27.9 1.5.5 How to identify what radionuclides in the drinking-water are contributing to screening levels being exceeded If either of the gross alpha or gross beta screening levels are exceeded, the validity of the result has been confirmed and additional measurements made have also exceeded the screening levels (having subtracted potassium-40 for gross beta measurements) (see Questions 1.5.3 and 1.5.4 for further details), the individual radionuclides contributing to the activity concentrations in the drinking-water need to be identified. All relevant information should be taken into account when deciding on what radionuclides are likely to be leading to the screening level being exceeded. Sources of information could be environmental monitoring data in the area and the catchment that the water is drawn from, knowledge of sites that could have led to discharges of radionuclides to the catchment and local geology. It is most likely that the source of radionuclides will be of natural origin, for example, radium-226 and radium-228. However, artificial radionuclides may also be present such as cobalt-60, strontium-90 and caesium-137. ? ? . 25MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S 1.5.6 How to assess if the individual dose criterion of 0.1 mSv y-1 has been exceeded using measurements of individual radionuclides in drinking-water The guidance level for a radionuclide is the concentration that, if present in drinking-water consumed throughout the year at a rate of 2 litres per day, would result in an individual dose of 0.1 mSv. If only a single radionuclide has been identified in the drinking-water, the activity concentration should be compared with the guidance level for that radionuclide (see Table 9.2 in chapter 9 of GDWQ and summarized in Table 1.1 below, for common radionuclides; guidance levels for other radionuclides are given in Table A6.1 in Annex 6 of the GDWQ). If the guidance level is exceeded, it is very likely that the individual dose criterion (IDC) of 0.1 mSv y-1 has been exceeded; further investigation is required (see Question 1.5.9). Table 1.1. Summary of WHO guidance levels for common radionuclides in drinking-water Radionuclide Guidance level (Bq L-1) 3H 10 000 14C 100 90Sr, 131I, 134Cs, 137Cs, 238U* 10 226Ra, 228Th, 230Th, 232Th, 234U*, 239Pu, 241Am 1 210Pb, 210Po, 228Ra 0.1 * Uranium is normally controlled on the basis of its chemical toxicity; the WHO guideline value for total content of uranium in drinking-water is 30 µg L-1, which is equivalent to 0.37 Bq L-1 of 238U or 234U. Key: tritium (3H); carbon-14 (14C); strontium-90 (90Sr); iodine-131 (131I); caesium-134 (134Cs); caesium-137 (137Cs); uranium-238 (238U); radium-226 (226Ra); thorium-228 (228Th); thorium-232 (232Th); uranium-234 (234U); plutonium-239 (239Pu); americium-241 (241Am); lead-210 (210Pb); polonium-210 (210Po) and radium-228 (228Ra). If several radionuclides have been identified, then the sum across radionuclides needs to be considered to check that it does not exceed unity, i.e. to check if the IDC has been exceeded. The equation to use is: ≤ 1 i ∑ CiGLi Where: Ci = the measured activity concentration above the respective limit of detection (LOD) of radionuclide i, GLi = the guidance level for radionuclide i, calculated using the default assumptions (adult, 2 L d -1) (see the theoretical example in Information Box 1.13). ? 26 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 1.13: Theoretical example to illustrate the evaluation of activity concentrations in a drinking- water sample against the IDC Measured activity concentrations are: Radium-226 = 0.8 Bq L-1 Radium-228 = < LOD Lead-210 = 0.05 Bq L-1 Polonium-210 = 0.03 Bq L-1 Summation equation = 0.8/1 + 0.05/0.1 + 0.03/0.1 = 1.6 As the summation is > 1 in this case, the IDC of 0.1 mSv y-1 is exceeded If the summation is ≥ 1, then the IDC is very likely to have been exceeded and further investigation is required (see Question 1.5.9). The guidance levels in the GDWQ are rounded to the nearest order of magnitude, as described in Question 1.3.4. Part of this investigation is to check if using these rounded guidance levels is too conservative (see Question 1.5.9). Care should be taken if the measurements being used to compare with the guidance levels are reported as less than the LOD (Information Box 1.14 provides an example from Sweden on this topic). These measurements are not actual activity concentrations but are a feature of the detection capability of the equipment used. Using measurements reported as < LOD as actual activity concentrations in the drinking-water sample will be conservative; the radionuclide may be present in the sample but the equipment used is unable to quantify the amount. Information Box 1.15 presents the approach to identifying an exceedance of the 0.1 mSv y-1 dose criterion used in the Euratom Drinking-Water Directive (EC, 2013). Information Box 1.14: Example of interpreting LODs when comparing with guidance levels In Sweden, in implementing the Euratom Drinking-Water Directive (EC, 2013) into national standards, the recommendation is to exclude radionuclides from the summation (and dose calculation) if their activity concentrations are below the LOD, given that the required LOD values in the Directive are very low (see Information Box 3.6 in Question 3.5). Information Box 1.15: Identifying an exceedance of the IDC in the Euratom Drinking-Water Directive A very similar approach to that used in the GDWQ for identifying an exceedance of the 0.1 mSv y-1 dose criterion is used in the Euratom Drinking-Water Directive (EC, 2013). In addition, activity concentrations are given which are 20% of the guidance levels. These values can be regarded as levels above which further investigation is warranted. Provided none of the measured activity concentrations exceed these “trigger levels”, there is no need to carry out the more complex process of summing across radionuclides to check if the IDC has been exceeded. . 27MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S 1.5.7 If the activity concentrations in drinking-water for the radionuclides measured do not exceed the guidance levels, does this mean that no further action is required Yes, in many cases. If only a single radionuclide has been identified in the drinking-water and the guidance level is not exceeded, the individual dose criterion (IDC) of 0.1 mSv y-1 is very unlikely to be exceeded. Monitoring of drinking-water should continue at the locations and at the frequency that are specified in the national drinking-water regulations for radiological parameters. If several radionuclides have been identified, but individually none of the measured activity concentrations exceed the guidance levels for the radionuclides measured, the sum across radionuclides needs to be considered to check that it does not exceed unity. The equation to determine this is shown in Question 1.5.6. If the summation is ≥ 1, then the IDC is likely to be exceeded and further investigation is required (see Question 1.5.9). However, there is an uncommon situation that is an exception to this: even if the summation is < 1, if any of the radionuclides uranium-238, radium-226 or strontium-90 have been identified as contributing significantly to the dose, the annual dose may have been underestimated. This is because the guidance levels for these radionuclides, which are rounded to the nearest factor of 10, are higher than the activity concentrations that would lead to a dose of 0.1 mSv y-1 by a factor of two or more7 (see Table 1.2 in Question 1.5.9). 1.5.8 If the 0.1 mSv y-1 individual dose criterion is exceeded, does this mean that the drinking-water is unsuitable for consumption No. Exceeding the individual dose criterion (IDC) is not an indication that the drinking-water is unsafe for consumption. However, if the measurements of radionuclides in drinking-water indicate that the IDC will be exceeded using default assumptions, additional steps are required to further investigate the situation; see Question 1.5.9. A radiation dose of 0.1 mSv y-1 represents a very low level of health risk and is typically at least a factor of 20 lower than doses that members of the public receive from all sources of radiation. Further, it is a factor of 10 lower than the reference level for exposure due to radionuclides in drinking-water recommended in the International Basic Safety Standards (BSS) (IAEA, 2014). Use of a water supply for drinking should not automatically be stopped if the annual dose is around the reference level of 1 mSv y-1 recommended in the International BSS (see Question 1.3.6), particularly if no other source is available or alternative sources are not suitable and affordable. In these circumstances, it may be appropriate to permit doses higher than 1 mSv y-1 for selected population groups, considering a balance of the overall risks, including the risk of not 7 Guidance levels are rounded to the nearest order of magnitude according to averaging the log scale values (to 10n if the calculated value was below 3 × 10n and to 10n+1 if value is 3 × 10n or above). ? ? 28 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER having a supply of drinking-water. The consequence of this would be the acceptance of a potential slight increase in radiological risks to health. It is important to note that, even if a water supply is not considered fit for human consumption due to the level of radionuclides, it will still be suitable for use for other purposes such as washing and cleaning. 1.5.9 What is the next step if a guidance level is exceeded or the sum across radionuclides exceeds unity, i.e. the individual dose criterion of 0.1 mSv y-1 is exceeded8 Consuming water that is calculated to give a radiation dose of between 0.1 and 1 mSv y-1 is not considered a radiological health risk (see Questions 1.3.6 and 1.5.8). However, if the individual dose criterion (IDC) of 0.1 mSv y-1 is exceeded, a number of steps should be taken and it is still necessary to apply optimization to try and reduce the prolonged exposure to the source of the drinking-water as far as reasonably possible. Although national and local authorities will need to thoroughly investigate the situation, in deciding what action to take, a key consideration is the extent to which the IDC is exceeded. No actions need to be implemented urgently if the assessed dose is below the reference level of 1 mSv y-1 specified in the International Basic Safety Standards (BSS). Step 1 – Use un-rounded values for the guidance levels to calculate the IDC The guidance levels in the GDWQ are rounded to the nearest order of magnitude to reflect the screening nature of the approach, with the assumptions made in the calculation of the guidance levels being conservative in most cases. Table 1.2 gives the guidance levels in the GDWQ, which are rounded to the nearest order of magnitude, and the actual activity concentrations that would give a dose of 0.1 mSv y-1. The use of the GDWQ guidance levels may lead to a situation where the calculated IDC indicates an exceedance of 0.1 mSv y-1 but the radiation dose is actually below 0.1 mSv y-1 (Information Box 1.16 provides a theoretical example and Information Box 1.17 provides an example from Brazil). Table 1.2. Guidance levels for common radionuclides Guidance Levels Radionuclide Half‑life Rounded valuea Bq L‑1 Un‑rounded values Bq L‑1 3H Tritium 12.5.y 10 000 7 610 14C Carbon-14 5 730 y 100 240 90Sr Strontium-90 29.12 y 10 4.9 131I Iodine-131 8.04 d 10 6.2 134Cs Caesium-134 2.062 y 10 7.2 137Cs Caesium-137 30 y 10 11.0 210Pb Lead-210 22.3 y 0.1 0.2 210Po Polonium-210 138.38 d 0.1 0.1 228Ra Radium-228 5.75 y 0.1 0.2 8 This answer is written on the basis that the IDC criterion in the GDWQ has been exceeded. Countries can set a different drinking-water standard or reference level (see Question 1.5.10); however, the stepwise approach given here would be the same if the country’s national standard/reference level were exceeded. ? . 29MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Guidance Levels Radionuclide Half‑life Rounded valuea Bq L‑1 Un‑rounded values Bq L‑1 234U Uranium-234 244 500 y 1 2.8 238U Uranium-238 4.468 x 109 y 10 3.0 228Th Thorium-228 1.913 y 1 0.6 230Th Thorium-230 7.54 x 104 y 1 0.7 232Th Thorium-232 1.405 x 1010 y 1 3.0 239Pu/240Pu Plutonium-239/240 2.41 x 104 y/6537 y 1 0.6 241Am Americium-241 432.2 y 1 0.7 a Guidance levels are rounded to the nearest order of magnitude according to averaging the log scale values (to 10n if the calculated value was below 3 × 10n and to 10n+1 if value is 3 × 10n or above). Information Box 1.16: Theoretical example of checking if the sum across radionuclides exceeds unity Measured activity concentrations are: Uranium-234 = 0.07 Bq L-1 Radium-228 = 0.05 Bq L-1 Lead-210 = 0.03 Bq L-1 Polonium-210 = 0.03 Bq L-1 Using rounded guidance levels in the GDWQ (shown in Table 1.2): Summation equation = 0.07/1 + 0.05/0.1 + 0.03/0.1 + 0.03/0.1 = 1.17 In this case the summation is > 1 and the IDC of 0.1 mSv y-1 is exceeded Using un-rounded activity concentrations (see Table 1.2): Summation equation = 0.07/2.8 + 0.05/0.2 + 0.03/0.2 + 0.03/0.1 = 0.725 In this case the summation is < 1 and the IDC of 0.1 mSv y-1 is not exceeded Table 1.2. (Continued) 30 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 1.17: Radionuclide concentrations in groundwater in Brazil (see also Section 4.1) Geometric mean radionuclide concentration in groundwater wells in Brazil (N=416 wells) Radionuclide Concentration (Bq L-1) Ci Ci/GLi a,b Guidance level (GL) rounded Ci/GLi a,b Guidance level (GL) un-rounded 238U 0.013 0.0013 0.0043 234U 0.045 0.045 0.016 230Th 0.007 0.007 0.01 226Ra 0.015 0.015 0.03 228Ra 0.06 0.60 0.30 232Th 0.0002 0.0002 0.00007 210Po 0.030 0.30 0.30 210Pb 0.04 0.40 0.20 Summation 1.37 (> 1) 0.86 (< 1) a Guidance levels from Table 1.2 b A bold value indicates where the value for Ci/GLi is lower using the unrounded guidance levels. Key: uranium-238 (238U); radium-226 (226Ra); thorium-228 (228Th); thorium-230 (230Th); uranium-232 (232U); lead-210 (210Pb); polonium-210 (210Po) and radium-228 (228Ra). Step 2 – Conduct a more detailed assessment of doses A more detailed assessment should consider both the characteristics of the water supply being investigated and the actual population that is consuming the drinking-water. Monitoring of the water supply and the water source will provide information on the stability of the activity concentrations in the water and whether they fluctuate throughout the year due to natural processes or possibly large variations in discharges of radionuclides to surface water sources. Taking further measurements could be considered to identify whether there are fluctuations in the activity concentrations of the radionuclides contributing most to the dose, particularly if this was not done at the screening stage (see Question 1.5.3). For assessing doses, the average doses over the year should be used. Where data are available or sufficient capacity exists to undertake such an analysis, national drinking-water consumption estimates can be used in calculating the guidance levels rather than using the guidance levels in the GDWQ, which are based on the default assumption of a consumption of 2 litres a day. The assessment of doses to children and babies drinking bottled milk reconstituted with drinking-water should also be considered, as appropriate (Annex 1 provides information on how to calculate doses to children). Step 3 – Consider options to reduce activity concentrations in drinking-water, including water treatment (see Question 1.5.11) For drinking-water supplies where it is confirmed that the IDC of 0.1 mSv y-1 is exceeded after undertaking steps 1 and 2, national authorities should consider whether it is a reasonable and practicable option to implement remedial actions to reduce the health risks from consumption of the drinking-water to as low as reasonably possible, depending on the extent of exceedance of the IDC and available resources. . 31MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S As part of the investigation of an exceedance of the IDC, any water treatment that is in place should be reviewed to see if further reductions could be achieved with additional or changed treatment that is straightforward to implement (see Question 3.2). Implementing new water treatment or making substantial changes to existing water treatment is likely to be a major undertaking, particularly for groundwater which is often untreated or only disinfected; it needs to be done carefully so as not to increase other possible health risks from the drinking-water supply. Discontinuing the use of the water for drinking purposes must be justified in terms of the overall benefit. Factors to be taken into account in making such a decision include the extent to which the reference level is exceeded, the costs of remediation and the availability of other drinking-water supplies. It is not appropriate to discontinue the use of the water supply without ensuring another safer option is available to consumers. A summary of the suggested actions for given levels of individual dose is shown in Table 1.3. Table 1.3. Summary of suggested actions for given levels of individual dose Individual dose from ingestion of drinking-water, mSv y-1 Intervention/action < 0.1 No action required. 0.1–1 Investigate exceedance of IDC, national standard or reference level. Actions should be proportionate to exceedance of dose criteria/ radiological health risk and available resources. Restrictions on the use of a drinking-water supply are not justified based on the radiological health risks. Reduce doses if possible. > 1 Investigate exceedance of national standard or reference level. Actions should be taken on a case-by-case basis and proportionate to exceedance of dose criteria/radiological health risk and available resources. Restrictions on the use of a drinking-water supply may be considered based on the radiological health risk but it is important to balance the overall risks, including the risk of not having a supply of drinking-water. Reduce doses if possible. 1.5.10 What are the considerations for establishing national standards based on the GDWQ and the International Basic Safety Standards For a non-emergency that can be controlled, the protection strategy should be commensurate with the associated radiation risks. The International Basic Safety Standards (BSS) require regulatory authorities to establish a reference level for radiation exposure due to radioactivity in drinking-water based on an effective dose that does not exceed a value of about 1 mSv y-1, as noted in the GDWQ. In setting up a national reference level, the prevailing technical, economic, environmental and societal circumstances need to be taken into account as part of an optimization process. Each situation will be different; and non-radiological factors such as the costs of remediation and the availability of other drinking-water supplies will need to be taken into account in reaching a final decision. Establishing a national standard at 0.1 mSv y-1 is appropriate for most countries where groundwater supplies with elevated levels of naturally occurring radionuclides are not present. Where there are elevated levels of naturally occurring radioactivity in groundwater and minimal options for alternative water sources or water treatment, a value higher than 0.1 mSv y-1, but generally less than the BSS reference level of 1 mSv y-1, may be appropriate for the affected population groups. ? 32 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Situations may arise where it may be appropriate to permit doses higher than 1 mSv y-1 for selected population groups, depending on the situation at the time, and considering a balance of the overall risks, including the risk of not having a supply of drinking-water. It is not appropriate to discontinue the use of the water supply without ensuring another safer option is available to consumers. A framework for setting a national standard or reference level within the recommendations and requirements of the International BSS and the GDWQ is given in Table 1.4. Table 1.4. Framework for setting a national standard or reference level Individual dose from ingestion of drinking-water, mSv y-1 National standard/reference level < 0.1 Set to be the individual dose criterion (IDC) in the GDWQ (0.1 mSv/y-1). (The operational values included in the GDWQ, expressed as screening and guidance levels should be used.) 0.1–1 Set in the range 0.1–1 mSv y-1 in accordance with the GDWQ and International BSS (see Question 1.3.6). (The operational values included in the GDWQ, expressed as screening and guidance levels, would need to be adapted.) > 1 Set on a case-by-case basis. A level can be set > 1 mSv y-1, depending on the situation at the time, and considering a balance of the overall risks, including the risk of not having a supply of drinking-water. A standard/reference level > 1 mSv y-1 is appropriate only for the affected population group. One option is to establish an interim standard/reference level, to allow time to achieve a lower value. (The operational values included in the GDWQ, expressed as screening and guidance levels, would need to be adapted.) In establishing criteria and/or reference levels to be used in national standards, the following considerations should be made by the competent authorities: • mapping of areas which have a geology leading to high levels of natural radioactivity in rocks and/or groundwater aquifers where radionuclides are mobile (see Information Box 1.18 for an example); • performing a population-weighted survey of where groundwater is used for drinking-water supplies; • determining whether water supplies are treated or amenable to treatment (taking into account that implementing new water treatment or making substantial changes to existing water treatment is likely to be a major undertaking and in many low-resource settings may not be feasible); • determining whether alternative supplies are available; • establishing a monitoring programme for radionuclides in drinking-water to identify any health risks, putting these in context with other risks from the water supply (namely microbial and chemical risks) and consideration of available resources; • establishing programmes to increase awareness of the public and stakeholders of the low health risks from radionuclides in drinking-water, particularly in situations where activity concentrations in excess of the guidance levels and IDC have been identified. Examples of setting reference levels and national standards for drinking-water are given in Information Box 1.19. . 33MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Information Box 1.18: Example of mapping radionuclides in groundwater in Queensland, Australia A screening programme was developed to provide initial data on the extent of radiological properties of groundwater supplies. The sampling was designed to include as many aquifer systems as possible, particularly those serving a community. Sampling regions were chosen to cover the range of aquifer lithology descriptors provided by the Queensland Water Resources Commission. The area to be covered was approximately 1.7 million km2 and so a sampling kit was developed and mailed with a questionnaire. Samples were received for 110 boreholes (59% of the 185 kits sent out) and analyses carried out for a range of naturally occurring radionuclides. Further details can be found in Kleinschmidt, Black & Akber (2011). Information Box 1.19: Examples of setting reference levels and national standards for drinking-water Japan After the Fukushima Daiichi nuclear power plant accident in Japan, from March 2011 until March 2012 provisional advisory index values for restrictions on tap water intake (for drinking and cooking purpose) were established for iodine-131 (300 Bq L-1 for adults and 100 Bq L-1 for infants) and for radioactive caesium (200 Bq L-1) (MHLW, 2011). Since 1 April 2012, a criterion called “the target level for management of radioactive materials in tap water” has been established (MHLW, 2012a). The target value is 10 Bq L-1 for radioactive caesium1, which replaced the previous provisional index levels for an emergency, and is used for the long-term non-emergency exposure situation. This level is derived directly from the guidance levels in the GDWQ. (It was not necessary to set a target value for iodine-131, as this radionuclide was no longer of concern due its very short radioactive half-life, ~eight days.) Jordan In Jordan, investigation identified that the average dose of the Ram aquifer (which is blended with available low radioactivity water resources before consumption) was between 0.65–0.75 mSv y-1 with radium-228 contributing between 70% and 85% of the overall dose. Subsequently, the Jordanian reference level in the drinking-water standard was raised from 0.1 to 0.5 mSv y-1 after consideration of the guidance from WHO in the GDWQ and careful review of the local environmental, social and economic conditions. The new reference level was justified based on the assessment that the potential health risks are tolerable and the net health benefits outweigh the potential health risks. Brazil The Brazilian Nuclear Energy Commission, the regulatory authority for drinking-water in Brazil, is adopting the following criteria in its drinking-water regulations. Reference level (1 mSv y-1) National reference level. Total dose from drinking-water should be below the national reference levels of 1 mSv y-1. Optimization range (0.1–1 mSv y-1) Whenever possible, protective actions should be planned to keep doses as low as reasonably achievable. In situations where the IDC of 0.1 mSv y-1 is not a practically achievable standard, no action is expected if total doses are above 0.1 mSv y-1 and below the reference level of 1 mSv y-1. Investigation level (0.1 mSv y-1) This level cannot be interpreted as a limit indicating that the drinking-water is unsafe but a trigger for further investigation. The Brazilian Nuclear Energy Commission will also establish a specific regulation containing a dose calculation procedure for situations where the gross alpha and gross beta screening levels are exceeded. 1 The sum of caesium-134 and caesium-137. 34 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.5.11 What are the possible options for reducing activity concentrations of radionuclides in drinking-water The options available to reduce the activity concentrations in drinking-water should be examined where the individual dose criterion (IDC), or reference level set within a country, is exceeded. Where remedial measures are contemplated, any strategy should first be justified, in the sense that it achieves a net benefit and overall does more good than harm, and is proportionate to the radiation risks in the context of other risks (e.g. microbiological, chemical). The main options that could be considered are briefly discussed below. The options chosen will be dependent on the specific situation and the factors to be taken into account in the choice of option include the extent to which the IDC or reference level is exceeded, the costs of the option and the availability of other drinking-water supplies. The information given here is of a general nature and a full evaluation of the options for a specific situation would need to be made. • Provide an alternative drinking-water supply. It may be possible to change to alternative sources of water, for example change from a groundwater source to a surface water source. Alternatively, there may be available groundwater sources with an underlying geology that do not lead to such high concentrations of naturally occurring radionuclides. Particular care should be taken to ensure that changes in source water do not lead to the introduction of additional, more significant risks that cannot be controlled or may be difficult to control (e.g. surface water sources which are often more polluted, particularly from microbial contamination). • Controlled blending of drinking-water supplies. The drinking-water of concern could be mixed with water containing no radionuclides or lower concentrations of radionuclides if more than one supply is available at the point of water treatment or post treatment. This is an effective method of reducing activity concentrations in drinking-water and has the added benefit of not generating radioactive waste products (see examples in Information Box 1.20. Blending is unlikely to be practical for small private or community supplies. • Implementing water treatment or the modification of existing water treatment. Water treatment plants with a combination of coagulation, sedimentation and sand filtration processes for treating surface water may remove about 30% to 100% of the suspended radionuclides present in the source water. Ion exchange filtration is particularly applicable to groundwater sources and can remove over 70% for naturally occurring radium and uranium. Further information on removal performance for common water treatment processes for some radionuclides can be found in Question 3.2. An example of a general checklist that could be used to assist with determining whether implementing additional water treatment may be the most appropriate and feasible option is given in Section I of USEPA (2005). Implementing new water treatment, or making substantial changes to existing water treatment is likely to be a major undertaking. – Water treatment options usually generate waste products that will contain the radionuclides removed from the water (see Question 3.3). – There are commercially-available treatment options that can be used in the home or private premises that will reduce radioactive contamination of drinking-water. These are: water filter systems for softening water that use a carbon filter with some ion exchange material (jug filters), and small reverse osmosis units. These products should be certified by an appropriate standards organization. Household water treatment options will generate waste products that will contain the radionuclides removed from the water (see Question 3.3). ? . 35MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Information Box 1.20: Examples of blending of drinking-water supplies Jordan In Jordan, the following remedial options were considered to address the situation of exceeding the national reference level in the Disi Water Conveyance Project supply: blending, reverse osmosis, nano-filtration, lime softening, ion exchange on selective resin and electro-dialysis. For each of the alternatives a feasibility study was performed on a pilot scale design. After considering remediation of the full yield of the Disi Water Conveyance Project supply of 100 million m3 y-1 using an environmental and cost–benefit analysis, it was decided that the most practical and sustainable option for Jordan was blending the Ram aquifer water (Disi) with available low radioactivity water resources (90 million m3 per year from Zai and 45 million m3 per year from Zara-Ma’en) (El-Naser et al., 2016). Blending typically reduces the annual doses from about 0.7 mSv y-1 (water from well field) to about 0.4 mSv y-1 at the point of consumption after blending (see Section 4.3 for further details). Canada The drinking-water for the city of Regina, Canada is taken from Buffalo Pound Lake, a shallow reservoir in the Qu’Appelle Valley through the Buffalo Pound Water Treatment Plant. The plant was commissioned in 1955. Before that time, all of the water came from deep wells with elevated levels of uranium concentration, higher than the national average. Since the 1960s, more and more surface water from Buffalo Pound Lake was mixed with well water before it was delivered to customers to reduce the concentrations of uranium in the drinking-water. Since the 1990s, almost 100% of the drinking-water for the city of Regina has been taken from surface water. Water quality monitoring data has shown that uranium concentration in the water decreased exponentially with increased amount of surface water being introduced into the water system (Health Canada, 2009). Available historical records from the database of the Canadian Radiological Monitoring Network showed that the annual average uranium concentration reduced from 12.3 µg L-1 in 1980 to 0.5 µg L-1 in 2016. 0 2 4 6 8 10 12 14 1980 1985 1990 1995 2000 2005 2010 2015 A n n u al a ve ra g e c o n ce n tr at io n o f to ta l u ra n iu m , µ g L -1 City of Regina, Canada Adapted with permission from Chen et al. (2017). A review of natural radionuclides in Canadian drinking-water (1975-16), Radiation Protection Dosimetry, pp. 1-11. Contains public sector information licensed under the Open Government Licence v3.0. 36 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 1 N ON ‑ eMe RG eNCY S I T UAT I ON S 1.6 RADON IN DRINKING-WATER 1.6.1 How does radon get into drinking-water Radon is produced from radium isotopes (produced during decay of naturally occurring uranium and thorium) and is present in the ground. As an inert gas, it dissolves readily in water, so if water passes through ground materials it can readily dissolve the radon and transport it over long distances9. The longest-lived isotope of radon, and consequently the most abundant in drinking-water supplies, is radon-222 which decays with a radioactive half- life of 3.8 days. Processes that enable the partial degassing of radon, such as water treatment, storage and distribution, usually reduce the radon concentration. However, drinking-water from natural springs, boreholes or wells, where there is a relatively short time between water extraction and its use, are more likely to result in an increased exposure to radon. Levels of radon in surface waters are typically very low because the gas is readily lost into the atmosphere. 1.6.2 Do national standards for radon in drinking-water need to be established No, not necessarily. The GDWQ does not provide guidance levels for radon because it is considered more appropriate to measure radon concentrations in indoor air rather than in drinking-water. A review of international research data (UNSCEAR, 2000) concluded that, on average, 90% of the dose attributable to radon in drinking- water comes from inhalation rather than ingestion. Radon dissolved in drinking-water can be released into the air when the water is used in activities associated with water being heated or agitated, such as boiling, 9 Where radon remains dissolved in drinking-water, the radionuclides lead-210 or polonium-210 (radon decay products) may become important contributors to the overall dose from the ingestion of drinking-water. ? ? . 37MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER showering, bathing and toilet flushing. However, the main source of radon in indoor air is likely to come from the rocks and soil underlying the building and not from drinking-water. WHO recommends a national reference level for indoor air of 100 Bq m-3 (WHO, 2009). If compliance with this level cannot be achieved under the prevailing country-specific conditions, the WHO radon handbook notes that the chosen reference level should not exceed 300 Bq m-3. In studies of the exposure from radon released into indoor air from water (Hess et al., 1987; Nazaroff et al., 1987), an overall transfer coefficient of radon from water to air of 10-4 was estimated, albeit with considerable variability. Using this transfer coefficient, a level of 1000 Bq L-1 of radon in tap water would be required to increase the radon concentration in indoor air by about 100 Bq m-3. If a country wants to set a national standard for radon in drinking-water, screening levels for radon in drinking-water should be based on the national reference level for radon in indoor air. Some countries have set national standards for radon in drinking-water (see Information Box 1.21). Information Box 1.21: Setting national standards for radon in drinking-water in the Euratom Drinking-Water Directive The Euratom Drinking-Water Directive (EC, 2013) sets a parametric value of 100 Bq L-1 for radon in drinking-water. Member States may set a level for radon at which it is judged inappropriate for it to be exceeded and below which optimization of protection should be continued, without compromising water supply on a national or regional scale. The level set by a Member State may be higher than 100 Bq L-1 but must be lower than 1 000 Bq L-1. Further, remedial action is deemed to be justified on radiological protection grounds, without further consideration, where radon concentrations exceed 1 000 Bq L-1 (EC, 2013). 1.6.3 At what points in the water supply chain should measurements of radon in drinking-water be made Samples should ideally be taken at the point of consumption. This is because radon concentrations can be reduced to very low levels between the water source and the point of consumption due to treatment processes that lead to agitation of the water, which promote degassing of the radon10, or distribution and storage, which lead to radioactive decay of the radon. Measurements made of radon at the water source may not therefore reflect the concentrations in consumed water and could be much higher. However, taking measurements of radon at the groundwater source are useful to determine the potential for radon in drinking-water to be present and to inform decisions on any remedial actions that may be necessary. 10 It should also be noted that the degassing of radon is promoted when other naturally occurring dissolved gases such as CO2 and N2 degas from groundwater. ? 38 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 1.6.4 What methods can be used for sampling and measuring radon in drinking-water supplies The precision of sampling and the subsequent measurement of radon in drinking-water is predominantly a function of whether the radon gas is lost from the sample during handling. Extreme care is needed when collecting the sample of water in the field and when handling the sample in the laboratory to prevent radon loss. Highly-trained staff are therefore required. Samples should be collected in containers made of materials that are impervious to radon, such as aluminium or glass. The water should be poured slowly into the container at a very low flow rate to avoid aeration and degassing of the radon from the sample. The transfer of the water sample to a Lucas Cell (a scintillation chamber for the detection of radon) in the field ensures that transport to the laboratory does not lead to any loss of radon from the sample. Due to the potential for loss of radon during sampling and handling, it is advisable to take multiple samples at the time of collection. The two main laboratory methods for measuring radon in drinking-water are the widely-used liquid scintillation counting and gamma spectrometry (see Question 3.5). Due to the short half-life of radon, ideally samples should be analysed on the day they are returned to the laboratory. It is important to note that radon will not be included in gross alpha screening measurements due to its volatility. Further information on methods for measuring radon in drinking-water can be found in the WHO handbook on indoor radon, Section 2.1.3 (WHO, 2009). 1.6.5 How can radon in drinking-water be managed when radon concentrations in the source water are high In situations where high radon concentrations have been identified or are suspected in groundwater, exposure from both inhalation and ingestion need to be considered in determining if steps are needed to reduce activity concentrations in drinking-water. Radon exposure from ingesting water is small compared to that from inhalation and the focus in controlling overall exposure is most likely to be on reducing radon concentrations in the indoor air from radon entering buildings from the ground. It is unusual for a building to have high levels of radon in indoor air caused solely by the water supply. For centralized water supplies with treatment, the most effective treatment option for high levels of radon is often the aeration of the water, which can remove up to 100% of the radon. This can lead to a build-up of radon in the air where people are working on everyday maintenance tasks if the water treatment works are covered. Firstly, measurements of radon in the air should be made to determine the levels in the working environment. If necessary, there are two options for controlling exposures to radon in this situation: ideally ventilation of the buildings or extraction of air to the outdoors should be implemented; however, where this is not possible, the exposure time of people working in environments with high radon concentrations can be controlled. ? ? . 39MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 1. N O N -E M E R G E N C Y S IT U A T IO N S Water treatment at the point of entry into the home may also reduce activity concentrations of radon in drinking-water. The most effective treatment option is aeration of the water, which can remove up to 100% of the radon; it is very important however, that the radon released from the water is extracted to the outdoors. Filtration with granular activated carbon with or without ion exchange can also be used, which is cheaper than aeration but less effective in reducing levels of radon in water (for example, Annanmaki & Turtianen, 2000). In situations where multiple dwellings are served by the same water supply, it may be practical and more cost-effective to remove high levels of radon at a point in the network that serves multiple dwellings rather than on an individual property basis. Where remedial measures are in place to manage radon levels in indoor air, these will also act to reduce the concentrations of radon in air from the use of drinking-water. However, it is advisable to continue to measure radon in drinking-water if the drinking-water supply comes from a nearby groundwater source. 40 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER EMERGENCY SITUATIONS Chapter 2 CHA P T e R 2 eM e RG eNCY S I T UAT I ON S 2.1 BACKGROUND ON EMERGENCY SITUATIONS AND CRITERIA FOR MANAGING DRINKING-WATER QUALITY 2.1.1 What is a radiation emergency situation A radiation emergency situation arises as a result of an accident, a malicious act or any other unexpected event that requires prompt action in order to avoid or reduce adverse consequences. Once an emergency arises, radiation exposure can be reduced by taking protective actions. 2.1.2 Are radionuclides in drinking-water likely to remain a long-term public health risk after a nuclear or radiological emergency No. It is very unlikely that radionuclides in drinking-water will remain a long-term public health risk after a nuclear or radiological emergency. Although open surface water sources will be the most vulnerable to contamination after a nuclear or radiological emergency involving releases to the atmosphere or water sources (see Question 2.3.2), activity concentrations in drinking-water from such sources will reduce quickly as they become significantly diluted due to mixing in large water volumes. It should be noted that if initial atmospheric deposition of ? ? 42 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER radionuclides from the emergency occurs onto snow pack or ice-cover, this may lead to a delay in any doses received from drinking-water from surface water sources until the snow/ice thaws. However, as for any initial contamination of surface waters, activity concentrations in drinking-water from such sources will also become significantly diluted very quickly due to mixing in large water volumes. Information Box 2.1 discusses the drinking-water restrictions imposed after the Fukushima Daiichi nuclear power plant accident. Direct contamination from a release of radionuclides into the environment will not occur to groundwater sources; any significant contamination of these drinking-water sources is very unlikely (see Question 2.3.2). Deliberate contamination of a drinking-water supply (i.e. a malicious act) could be to a surface or groundwater source or directly into the water supply. In this case, radionuclides will only be present in drinking-water for a very short period of time at high activity concentrations. Radionuclides in drinking-water are therefore very unlikely to remain a long-term health risk in this situation. Information Box 2.1: Example of restrictions placed on drinking-water after an accident in Japan After the Fukushima Daiichi nuclear power plant accident in Japan, the restriction of drinking-water intake was implemented in 20 water supply utilities serving a total population of about 14 million. The longest restriction was 12 days, except for one location (population about 4 000), where the restriction on intake for infants lasted 51 days (see Section 4.5 for more details). 2.1.3 When does an emergency situation end and what does this mean with respect to drinking-water quality The transition from an emergency situation to a non-emergency (existing) situation and subsequent termination of the emergency will be a decision made by the responsible authority, based on the prevailing conditions after relevant and pre-set conditions and other criteria have been met (ICRP, 2009; IAEA, 2015; IAEA 2018). During the transition period, the criteria for drinking-water in emergency situations apply (IAEA, 2015; 2011). Once the relevant authority has declared an end to the emergency situation, any remaining radionuclides in drinking-water and its sources in the longer term resulting from the emergency should be treated as a non-emergency situation (where the criteria for drinking-water in non-emergency situations in the GDWQ apply, see Question 1.3.1). The international Safety Standards Series on preparedness and response for a nuclear or radiological emergency (IAEA, 2011) indicates that as soon as possible, the WHO guidance in the GDWQ should be used to determine if drinking-water is suitable for long- term consumption after the emergency phase of the accident has ended. ? . 43MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 2. E M E R G E N C Y S IT U A T IO N S 2.1.4 Are there any international standards and criteria that apply for drinking-water quality in emergency situations Yes. There are the IAEA Safety Standards Series on preparedness and response for a nuclear or radiological emergency, which includes General Safety Requirements No. GSR Part 7 (IAEA, 2015) and General Safety Guide No. GSG-2: Criteria for use in preparedness and response for a nuclear or radiological emergency (IAEA, 2011). These contain criteria for drinking-water that apply for emergency situations. These standards are co-sponsored by a number of international organizations, including WHO. According to these international standards, governments are responsible for ensuring that protection strategies are developed, justified and optimized at the preparedness stage for taking effective emergency response actions in a nuclear or radiological emergency. The protection strategy is expected to include criteria for taking emergency response actions including those for drinking-water. Generic criteria in terms of projected radiation doses for planning purposes and Operational Intervention Levels (OILs) in terms of activity concentrations in emergency situations – which would warrant urgent protective actions such as banning consumption of drinking-water – are included in GSR Part 7 and GSG-2, respectively (IAEA, 2011; 2015). • GSR Part 7 provides generic criteria for the projected doses at which restrictions on the consumption of drinking-water should generally be implemented. These generic criteria are to be used for developing operational criteria in terms of directly measurable quantities that can be used in an emergency situation to impose these restrictions. • GSG-2 provides default OILs in terms of gross alpha and gross beta activity concentrations (i.e. OIL5) and in terms of activity concentrations for a large number of radionuclides in drinking-water (OIL6) at which restriction on the consumption of drinking-water should generally be imposed in a nuclear or radiological emergency. The screening criteria (OIL5)11 are: OIL5 – Gross alpha: 5 Bq Kg-1 OIL5 – Gross beta: 100 Bq Kg-1 The OIL5 and OIL6 values for drinking-water are derived on the basis of a generic dose criterion of 10 mSv in the first year after the emergency, assuming that no protective actions are taken, and that all drinking-water is contaminated at the OIL activity concentration throughout the year and using the most restrictive age group and consumption rates. The OIL values are therefore very conservative as activity concentrations in drinking-water after a nuclear or radiological emergency will reduce rapidly after the initial contamination event and will not remain at a constant level for the whole year. Ten mSv is 10% of the generic criterion of 100 mSv in the first year for implementing early protective actions and other response actions during emergency situations (IAEA, 2015). The use of 10 mSv ensures that the dose from all exposure pathways will not exceed the 100 mSv criterion. Further details on the OILs and their use are provided in Question 2.3.1 and 2.4.1. Based on the above-mentioned international standards, individual countries may develop their own national criteria, taking into account the criteria provided in these international standards as well as local prevailing circumstances (e.g. environmental, demographic, social, political, economic and other factors). The aim of giving consideration to all these various factors is to ensure that the national criteria guide justified and optimized emergency response actions. Any further restrictions on drinking-water extending into the longer term might be implemented with the aim of eventually achieving a reference level (or national standard) that takes into account the WHO individual IDC of 0.1 mSv y-1 and the International Basic Safety Standard (BSS) reference level of 1 mSv y-1, balancing the prevailing technical, economic, environmental and societal circumstances as part of an optimization process. 11 1 Bq Kg-1 = 1 Bq L-1 in water ? 44 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 2 eM e RG eNCY S I T UAT I ON S 2.2 HEALTH RISKS FROM DRINKING- WATER IN THE EVENT OF A NUCLEAR OR RADIOLOGICAL EMERGENCY 2.2.1 What radionuclides are likely to be of concern in drinking-water during a nuclear or radiological emergency The radionuclides likely to be of concern in drinking-water in a nuclear or radiological emergency depend on the type of emergency and types of facilities and activities that might be involved (e.g. accidents at nuclear power plants, accidental releases from industrial or medical facilities using radionuclides and transport accidents) as well as their ability to enter the drinking-water sources for drinking-water supplies (Brown, Watson & Nisbet, 2015; WHO, 2017a). Table 2.1 gives the radionuclides that are potentially relevant for exposure from drinking-water following a nuclear or radiological emergency, including the incident scenarios and routes to surface water contamination. Although radiological incidents arising from industrial uses of radionuclide sources are common (UNSCEAR, 2016), they are very unlikely to give rise to the contamination of drinking-water and radionuclides specific to these types of incidents are therefore not included in the table. Information Box 2.2 provides an example of the sampling that determined the most critical radionuclides following an accident. ? . 45MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 2.2: Example of the identification of important radionuclides after an accident In the case of the Fukushima Daiichi nuclear power plant accident in Japan, the identification of individual radionuclides revealed that caesium-134, caesium-137 and iodine-131 were of importance for drinking-water immediately after the accident. Activity concentrations of other radionuclides measured, including strontium-90 and tritium, were much lower. Source: WHO (2012). Table 2.1. Radionuclides potentially relevant for drinking-water following a nuclear or radiological emergency Radionuclides Incident scenarios where used and/or produced Routes to surface water contaminationa 3H By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 60Co By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 90Sr / 90Y By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 95Zr / 95Nb By-product of nuclear reactor operations Release to atmosphere 99Mo / 99mTc Medical (nuclear medicine Technetium generators) By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 103Ru 106Ru By-product of nuclear reactor operations Release to atmosphere 132Te By-product of nuclear reactor operations Release to atmosphere 131I Medical (nuclear medicine facilities used for diagnostic and/or therapeutic procedures) By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 134Cs 136Cs 137Cs / 137mBa By-product of nuclear reactor operations Release to atmosphere Direct contamination of water 140Ba / 140La By-product of nuclear reactor operations Release to atmosphere 144Ce By-product of nuclear reactor operations Release to atmosphere 235U Reactors and nuclear weapons Direct contamination of water 238Pu 239Pu By-product of nuclear reactor operations Nuclear weapons (239Pu) Release to atmosphere Direct contamination of water 241Am Medical diagnostics By-product of nuclear reactor operations Release to atmosphere Direct contamination of water Radioactive daughters are mentioned where they are the dominant contributor to the health risk and otherwise are implicitly included in the list. a Releases into the atmosphere can lead to deposition onto water sources and treated water or indirectly into water sources via run-off from catchment areas. Source: Adapted from Brown J, Hammond D & Wilkins BT (2008b). Handbook for assessing the impact of a radiological incident on levels of radioactivity in drinking-water and risks to water treatment plant operatives: supporting scientific report. HPA-RPD-041, Chilton, UK. © Crown copyright. Key: tritium (3H); cobalt-60 (60Co); strontium-90 (90Sr ); yttrium-90 (90Y); zirconium-95 (95Zr ); niobium-95 (95Nb ); molybdenum-99 (99Mo ); technetium- 99m (99mTc ); ruthenium-103 (103Ru); ruthenium-106 (106Ru); tellurium-132 (132Te); iodine-131(131I); caesium-134 (134Cs); caesium-136 (136Cs); caesium-137 (137Cs); barium-137m (137mBa); barium-140 (140Ba); lanthanum-140 (140La ); cerium-144 (144Ce ); uranium-235 (235U); plutonium-238 (238Pu); plutonium-239 (239Pu) and americium-241 (241Am). 46 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER 2.2.2 Do children require stricter protection than adults when establishing criteria for the consumption of drinking-water after a nuclear or radiological emergency For emergency situations, the criteria established in international standards (IAEA, 2015; 2011) take into account the members of the public who are the most vulnerable to radiation exposure (i.e. children and pregnant women). These criteria are derived using the most restrictive age dependent dose conversion factors and ingestion rates (i.e. those for infants) to ensure that the most vulnerable members of the population are protected from relatively high short-term doses. The assumptions made in the derivation of the operational criteria are conservative. Some countries may decide to set different activity concentration criteria for different age groups for specific radionuclides (see Information Box 2.3). This approach may lead to challenges in implementation of different actions for different population groups and difficulties in conveying a clear message to the public why some members of their families can consume the drinking-water while others cannot do so. Information Box 2.3: Example of setting different criteria for children In Japan after the Fukushima Daiichi nuclear power plant accident, the provisional regulation values for drinking- water were established considering the most susceptible age groups. For radioactive caesium (137Cs and 134Cs), the provisional regulation value was the same for adults, young children and infants (300 Bq Kg-1) (Iwaoka, 2016). However, for iodine-131, it was considered that the adverse effects on the thyroid are higher for infants than other age groups. A value of 300 Bq Kg-1 was set for adults and children and a lower value was set for infants for both drinking-water and water used for making bottled milk (100 Bq Kg-1) taken from the CODEX Standard (CODEX, 2001). 2.2.3 How are health risks from radionuclides in drinking-water likely to compare to those from other exposure pathways in nuclear or radiological emergencies It is very unlikely that radionuclides in drinking-water will remain a long-term public health risk after a nuclear or radiological emergency, as explained in Question 2.1.2. With the exception of cases of deliberate contamination of a drinking-water supply system, at the time of the emergency, external exposure from radionuclides on the ground and internal exposure from inhalation of radionuclides in the air are expected to be the pathways that are dominant contributors to the dose of the public living in the vicinity of the accident site. With increasing distance from the accident site, internal exposure from the ingestion of radionuclides in food, milk and drinking-water becomes dominant, but the doses will be significantly lower than those received by people closer to the accident site. ? ? . 47MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 2. E M E R G E N C Y S IT U A T IO N S Depending on the radionuclides released into the environment, doses over the long term will be dominated by external exposure and/or ingestion of foods and not the ingestion of drinking-water. This was observed after the nuclear accident at the Fukushima Daiichi nuclear power plant (WHO, 2012; WHO, 2013) and is described in Information Box 2.4. Information Box 2.4: Example of the importance of exposure pathways after an accident After the Fukushima Daiichi nuclear power plant accident in Japan on 11 March 2011, the Japanese authorities measured radionuclide levels in drinking-water; the first sample of drinking-water was collected in Fukushima Prefecture on 16 March 2011. Levels were only elevated for a limited period in the months following the accident. Within Fukushima Prefecture, doses to people living in each district were estimated for the period March 2011– March 2012. For example, in Iitate village, the radiation dose to 1-year old children from radionuclides in drinking- water was estimated to be less than 5% of the total dose from all external and internal exposures, including ingestion of food. 48 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 2 eM e RG eNCY S I T UAT I ON S 2.3 MEASURING RADIONUCLIDES IN DRINKING-WATER IN AN EMERGENCY SITUATION 2.3.1 What screening methods can be used in nuclear or radiological emergencies to measure radionuclides in drinking-water Measurements of gross alpha and gross beta activity concentrations, designed and used for routine monitoring of drinking-water, can also be used in a nuclear or radiological emergency situation. However, these screening techniques do not identify the individual radionuclides present or their activity concentrations. An advantage of using screening methods is that capability may already be in place within water authorities and laboratories in a country, whereas equipment for measuring individual radionuclides may not be available (see Question 3.5). In many circumstances, gross alpha and gross beta screening methods could be used to demonstrate that activity concentrations are below the operational intervention levels (OILs) set for an emergency situation, thus saving time and resources for detailed radionuclide analysis. The OILs for both gross alpha and gross beta activity concentrations (OIL5) in the IAEA Safety Guide GSG-2 are intended for use as screening criteria in nuclear or radiological emergencies (IAEA, 2011) (see Questions 2.1.4 and 2.4.1). The OIL5 values are not the same as the gross alpha and gross beta screening levels for non-emergency situations (see Question 1.3.3). Although screening methods are appropriate under most situations, depending on the measurement techniques being used, some radionuclides would not be detected by gross alpha or gross beta activity analysis (such as tritium, selenium-75, niobium-95, ruthenium-103 or ytterbium-169) and therefore not included in the gross measurement. Some gaseous or volatile radionuclides, such as isotopes of iodine will also not be detected as losses of the radionuclides will occur during ? . 49MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER the analytical procedure. If it is suspected that these radionuclides have been released during an emergency and may be present in drinking-water, it is necessary to also carry out radionuclide-specific measurements. If the radionuclides released during an emergency are known, particularly in the case of a small-scale emergency or where there are only a limited number of drinking-water supplies that need to be measured, it may be most efficient to measure the individual radionuclides in the first instance and directly compare these with the radionuclide-specific criteria, such as the OIL6 values. Countries may set their own screening levels for drinking-water based on their own national emergency criteria (see Question 2.1.4). An example of setting screening levels is given in Information Box 2.5. Information Box 2.5: Example of setting screening levels for emergencies The Environment Agency of the United Kingdom of Great Britain and Northern Ireland developed guidance on monitoring drinking-water using gross alpha and beta screening methods. Emergency screening levels in terms of gross activity concentrations have been developed (see below) that can be used in the event of a radiation incident to determine if intervention is required to reduce activity concentrations in drinking-water. Emergency screening levels for gross alpha and gross beta activity concentrations in drinking-water in the United Kingdom Type of monitoring emergency screening level (Bq L‑1) Gross alpha activity 5 Gross beta activity 30 (For comparison, screening levels for non-emergency situations are 0.1 Bq L-1) and 1 Bq L-1) for gross alpha and gross beta, respectively.) Source: Brown, Watson & Nisbet, 2015. 2.3.2 During a nuclear or radiological emergency, what types of water source are likely to be affected Water sources, such as rivers and reservoirs, are likely to be most vulnerable to radionuclide contamination after a nuclear or radiological emergency involving releases of radionuclides to the atmosphere or water sources. Under such circumstances, in addition to direct deposition to surface water sources, run-off from surrounding land, and thawing of snow pack or ice-cover contaminated with radionuclides can also enter surface waters over the long term. This excludes deliberate contamination of water supplies with radionuclides (e.g. malevolent acts), which may affect the water in reservoirs or at distribution points. Direct contamination will not occur to underground aquifers immediately and contamination of these drinking-water sources is only likely to occur in the long term if radionuclides percolate down through the soil and rocks. Ingress of radionuclides could also occur through poorly protected wells and bore heads, particularly if flooding is associated with an accident. ? 50 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Rainwater that is collected in tanks and cisterns for drinking-water on domestic premises could contain radionuclides if rain occurs while the plume is overhead. Exposure from consuming this water would only be for a short period as radionuclides would rapidly become diluted with further rainfall after the plume has passed and consumption of this water will be limited by the size of the storage tank. The IAEA international Safety Standard (GSR Part 7) (IAEA, 2015) suggests considering precautionary actions around nuclear facilities to protect drinking-water supplies that use rainwater or other untreated surface water from direct contamination, as part of emergency planning. 2.3.3 During a nuclear or radiological emergency, which water sources are a priority for monitoring Priority should initially be given to the monitoring of water supplies taken from surface water sources under the radioactive plume following a release of radionuclides to the atmosphere. These water sources are likely to have the highest levels of radionuclides and become contaminated quickly after the accident. The levels of radionuclides in the water extracted will depend on how far downstream from the accident extraction occurs, as levels will decrease with distance due to dispersion in the atmosphere and dilution in the water. Run-off from the catchment area of surface waters can lead to a longer-term source of radionuclides in drinking-water supplies and, depending on the nature of the catchment area and the size of the release, additional water sources to those initially contaminated by the radioactive plume could be affected. It is unlikely that the levels of radionuclides would be of public health concern (see Question 2.1.2) but monitoring of water supplies at treatment works or in stored water supplies should be carried out to demonstrate that activity concentrations are low. In areas where the initial atmospheric deposition of radionuclides is onto snow pack or ice-cover, the planning of monitoring needs to take account of both any initial contamination of surface waters and also contamination of surface water that may occur following the thawing of the snow pack and ice, as noted in Question 2.1.2. This may require monitoring over an extended period depending on the rate of thaw and subsequent release of radionuclides from the top of the ice/ snow pack into surface waters. It is important that measurements are made that are representative of the drinking-water being consumed for comparison with operational criteria, e.g. the operation intervention levels (OILs). If water is treated before consumption, the water should be monitored after treatment because treatment can reduce the activity concentrations of many radionuclides in the water (see Question 3.2). A long-term drinking-water monitoring programme should include monitoring of groundwater supplies to provide reassurance that activity concentrations in these sources remain low. ? . 51MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 2. E M E R G E N C Y S IT U A T IO N S CHA P T e R 2 eM e RG eNCY S I T UAT I ON S 2.4 MANAGING EXCEEDANCES OF CRITERIA FOR DRINKING-WATER IN EMERGENCY SITUATIONS 2.4.1 How are operational intervention levels for drinking-water used in the event of a nuclear or radiological emergency If the gross alpha or gross beta screening criteria established for emergencies (operation intervention levels (OILs), e.g. OIL5 values) are not exceeded after measurements have been made on drinking-water, all members of the public, including infants, children and pregnant women, can drink the water. If either of the screening criteria is exceeded12, measurements of activity concentrations of individual radionuclides are required before any judgement is made whether drinking-water consumption should be restricted. This staged approach (shown in Figure 2.1) is consistent with that recommended in the GDWQ for non-emergency situations, where screening levels and guidance levels are used. The General Safety Guide No. GSG-2 on Criteria for use in preparedness and response for a nuclear or radiological emergency (IAEA, 2011) provides values of activity concentrations (OIL6) for more than 300 radionuclides. The OIL6 values are very conservative as they have been calculated using the assumption that the activity concentrations in drinking-water would remain at this level for a whole year, which is extremely unlikely to be the situation following an emergency situation (see Question 2.1.4). If the activity concentration of any radionuclide exceeds its OIL6 value, it may not be suitable for consumption and actions to reduce activity concentrations in the drinking-water and doses from 12 If the gross beta screening criteria (OIL5) is exceeded, the contribution from potassium-40 should be subtracted from the measurement(s) following a separate determination of the total potassium in the drinking-water, if this has not already been done. ? 52 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER consumption of drinking-water should be considered (see Question 2.4.2). However, as the determination of OIL6 values considers the most vulnerable members of the public (e.g. infants and pregnant women) and it is assumed that all of the drinking-water is contaminated for a full year, exceeding the criteria does not necessarily mean that the drinking-water is unsuitable for consumption. Further investigation, including consideration of actual consumption rates and additional measurements, would be needed (see Question 2.4.2 for more information). It is important that information on the radionuclides present in drinking-water are known as quickly as possible in an emergency situation. It is anticipated that screening of drinking-water supplies against the OIL5 and OIL6 values could be implemented within about a week to confirm any precautionary restrictions placed on the consumption of drinking- water immediately after the emergency (IAEA, 2011). Figure 2.1. Staged approach for applying the OILs in emergency situations No No Yes Yes Determine gross α and β activity OIL5 exceeded OIL6 exceeded Determine radionuclide concentration Suitable for consumption May not be suitable for consumption except in exceptional circumstances Source: IAEA (2011); pp. 40 (https://www-pub.iaea.org/books/iaeabooks/8506/Criteria-for-Use-in-Preparedness-and- Response-for-a-Nuclear-or-Radiological-Emergency-General-Safety-Guide ). Reprinted with permission of the publisher. . 53MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 2. E M E R G E N C Y S IT U A T IO N S 2.4.2 What actions can be considered if the criteria for drinking-water in emergency situations are exceeded ? Are there any special actions for small water supplies, including community supplies If drinking-water supplies become contaminated with radionuclides after a nuclear or radiological emergency, it is likely that some of the contaminated water will be consumed. As explained in Question 2.1.2, it is very unlikely that radionuclides in drinking-water will remain a long-term public health risk and radionuclides are only likely to be present for a very short period of time at relatively high activity concentrations. Effective communication of the risks associated with consuming this drinking-water is therefore important both in the case that drinking-water contains radioactivity at concentrations below the operational intervention levels (OILs) set, and if they are above these levels for a limited period of time (see Question 2.4.1). If the OILs are exceeded, the international standards recommend that restrictions on the consumption of non-essential drinking-water are implemented as a protective action (IAEA, 2015; 2011). If consumption of the supplied drinking-water is unavoidable because its restriction may lead to dehydration and replacement water is not available, the drinking-water can be consumed until a replacement is available. However, even if the drinking-water is consumed, it is not likely to pose a significant health risk as discussed in Question 2.1.4. While there may be a slight increase in the radiological risk to health, the risk of not having water for consumption is a far more significant risk to health. If radioactive iodine has been released, the international standards recommend that implementation of iodine thyroid blocking is considered (WHO, 2017b). Further information about criteria for iodine thyroid blocking implementation is available elsewhere (IAEA, 2011; WHO, 2017b). There are different water management and remedial options that could be considered for drinking-water that exceeds the pre-established criteria for emergency situations and these options are briefly discussed below. The options chosen will be dependent on the specific situation; factors to be taken into account in the choice of option include the extent to which the emergency criteria are exceeded, the costs of the option and the availability of other drinking-water supplies. The information given here is of a general nature and a full evaluation of options for a specific situation would need to be made depending on the country context and resources. Further details of possible options can be found in handbooks on recovery after radiation incidents, for example the UK recovery handbooks for radiation incidents 2015 – Drinking‑water supplies handbook (Brown, Watson & Nisbet, 2015). • Continue the use of the drinking-water supply supported by a detailed monitoring programme. If the radionuclide has a half-life of less than about a week, it may not be necessary to consider any specific option for reducing activity concentrators in the drinking-water due to the short timescale of the exceedance. Relying on normal water treatment, supported by monitoring and good risk communication to the public, may be the most practicable option, particularly for small community supplies. • Provide an alternative drinking-water supply that does not contain radionuclides, such as bottled water or water from an unaffected area brought in by tankers. Water from the supply can still be used for sanitation purposes. As part of an emergency response plan, water utilities should have developed plans for providing and distributing emergency supplies of drinking-water. It is important to ensure that the alternative supply does not introduce additional, more significant risks (as described below). • Change the water source to one that does not contain radionuclides above the criteria (changes to water abstraction point or location of water source). There may be water sources available that are not affected or are much less affected by the consequences of the emergency. It may also be possible to change from a surface water source ? 54 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER to a groundwater source. Particular care should be taken to ensure that changes in source water do not lead to the introduction of additional, more significant risks that cannot be controlled or may be difficult to control (e.g. surface water sources which are often more polluted, particularly from microbial contamination). • Controlled blending of drinking-water supplies. The drinking-water of concern could be mixed with water not affected by the consequences of the emergency, or with water that was less affected and containing lower concentrations of radionuclides, if more than one supply is available at the point of water treatment or post treatment. This is an effective method of reducing activity concentrations in drinking-water and has the added benefit of not generating radioactive waste products. Blending is unlikely to be practical for small private or community supplies. • Implementing water treatment or the modification of existing water treatment. Water treatment plants with a combination of coagulation, sedimentation and sand filtration processes for treating surface water may remove between 30% and 100% of radionuclides present in the source water, depending on the radionuclide. Further information on removal performance for common water treatment processes for some radionuclides can be found in Question 3.2. An example of a general checklist that could be used to assist with determining whether implementing additional water treatment may be the most appropriate and feasible option is given in Section I of USEPA (2005). Implementing new water treatment, or making substantial changes to existing water treatment, is likely to be a major undertaking and is very unlikely to be implemented quickly. – Water treatment options usually generate waste products that will contain the radionuclides removed from the water (see Question 3.3). – There are commercially available treatment options that can be used in the home or private premises that will reduce radioactive contamination of drinking-water. These are: water filter systems for softening water that use a carbon filter with some ion exchange material (jug filters), and small reverse osmosis units. These products should be certified by an appropriate standards organization. Household water treatment options will generate waste products that will contain the radionuclides removed from the water (see Question 3.3). These types of units are more likely to be practical for small communities or where only a small water-supply is affected, as they will not be accessible on a large scale and their use will need to be carefully controlled to ensure they are effective and waste filters are handled appropriately. Information Box 2.6 and Information Box 2.7 discuss remedial activities undertaken in response to the Fukushima Daiichi nuclear power plant accident in 2011. Information Box 2.6: Covering open storage reservoirs During a release of radionuclides to the atmosphere, radionuclides can be deposited directly onto source water at the abstraction point and during treatment or onto treated water being stored prior to distribution. In this case, taking actions to protect the drinking-water supply systems such as covering open water storage reservoirs to protect it from direct contamination via dry and wet deposition may be effective if implemented before or shortly after the release. For example, water treatment basins were covered in Japan after the Fukushima Daiichi nuclear power plant accident. Information Box 2.7: Restricting consumption of drinking-water after an accident In the case of the Fukushima Daiichi nuclear power plant accident on 11 March 2011 in Japan, restrictions on tap water intake by infants were implemented by 20 water supply utilities in a total of five prefectures because the index value of radioactive iodine (100 Bq Kg-1) was exceeded for infants. Most of the restrictions lasted two to three days in prefectures other than Fukushima Prefecture. All restrictions on the infants’ intake were lifted by 10 May 2011. An intake restriction for all age groups was only implemented for a small-scale water supply utility in Fukushima Prefecture on 21 March 2011; this was because the level of radioactive iodine exceeded 300 Bq Kg-1 (index value for adults). This restriction was lifted on 1 April 2011. During the period of the restrictions, distribution of bottled water or via tankers was carried out. Further information can be found in Section 4.5. . 55MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 2. E M E R G E N C Y S IT U A T IO N S 56 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER SUPPORTING INFORMATION Chapter 3 CHA P T e R 3 S U P POR T I N G I N FO RMAT I ON 3.1 DOES BOILING WATER REDUCE THE EXPOSURE FROM RADIONUCLIDES IN DRINKING-WATER ? No. Boiling will not reduce concentrations of radionuclides in drinking-water. However excessive (i.e. continuous or extended) boiling may lead to higher concentrations of radionuclides due to the reduction in volume of water from boiling (see Information Box 3.1). Information Box 3.1: Reducing activity concentrations by boiling drinking-water Tests in Japan after the Fukushima Daiichi nuclear power plant accident (Tagami & Uchida, 2011) showed no iodine-131 loss from the tap water with either short-term boiling (1–10 minutes) or prolonged boiling (up to 30 minutes). Long-term boiling resulted in increased concentrations of iodine-131 due to a threefold reduction in volume. ? 58 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 3 S U P POR T I N G I N FO RMAT I ON 3.2 HOW EFFECTIVE ARE WATER TREATMENT OPTIONS IN REMOVING RADIONUCLIDES FROM DRINKING-WATER ? Surface water typically undergoes more treatment than groundwater, particularly water sources with high turbidity (large amounts of suspended particulate matter) and high microbial content (see Table 3.1). Removal of radionuclides is likely to be higher for water undergoing more extensive treatment. For water sources with less treatment (e.g. many groundwater sources), generally there will be less removal of contaminants, including radionuclides. Table 3.1. Surface and groundwater characteristics Characteristic Surface water Groundwater Turbidity High Low Dissolved minerals Low-moderate High Microbial content High Low Temporal variability Very high Low In general, treatment that combines coagulation with sedimentation or filtration should be effective at removing suspended radionuclides to some extent, with the effectiveness ranging from about 30% to 100%, and typically about 70% for the main naturally occurring radionuclides (see Table 3.2). Ion exchange filters, which are more commonly used for groundwater, are particularly effective for radium and uranium, removing over 70% of these radionuclides. However, these are often installed to remove nitrates from water and these may compete with radionuclides in terms of their preferential removal. Information Box 3.2 provides an example of filtration activities after the Fukushima Daiichi nuclear power plant accident. Table 9.4 in Chapter 9 of the GDWQ, adapted below, gives a summary of the removal performance for some common water treatment processes for some elements. For further details, a review of the effectiveness of different water treatment processes and a description of the factors that can influence this can be found in Brown, Hammond & Wilkins (2008b) and USEPA (2005). References for treatment technologies specific to radionuclides are also provided in Annex 6 of the ? . 59MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N GDWQ. Further information on techniques for removing uranium, radium, lead and polonium and their likely effectiveness can also be found in Annanmaki & Turtianen (2000). It should be noted that the removal performance will be very specific to the water source and treatment undertaken and the information provided is only indicative of the reductions in concentrations that could be expected. Table 3.2. Water treatment performance Element Coagulation Sand filtration Activated carbon Lime-soda softening Ion-exchange Reverse osmosis Strontium XX XX X XXXX XXX XXXX Iodine XX XX XXX X XXX XXXX Caesium XX XX X XX XXX XXXX Radium XX XXX XX XXXX XXXX XXXX Uranium XXXX X XX XXXX XXXX XXXX Plutonium XXXX XX XXX X XXXX XXXX Americium XXXX XX XXX X XXXX XXXX Tritium Not possible to remove Key: x = 0–10%; xx = 10–40% removal; xxx = 40–70% removal; xxxx = > 70% removal. Source: Adapted from Table 9.4, Chapter 9 of WHO (2017a). Information Box 3.2: Effectiveness of water treatment in removing iodine-131 (131I), caesium-134 (134Cs) and caesium-137 (137Cs) After the Fukushima Daiichi nuclear power plant accident, measurements were made in some water treatment plants to study the effectiveness of removing 131I and radioactive caesium (134Cs and 137Cs) during water treatment. Iodine-131 In two water treatment plants it was found that coagulation and sedimentation did not remove 131I (concentrations in raw water:treated water of 2.9 Bq L-1:2.8 Bq L-1 and 5.4 Bq L-1:5.7 Bq L-1 were observed) (Kosaka et al., 2012; 2014). In these cases, 131I in raw water was considered to be present in a dissolved form and not as particulate. It was found that the granular activated carbon process did remove 131I. Reductions of 2.8 Bq L-1 to 1.9 Bq L-1 were observed in a water treatment plant, i.e. a removal of 34%. Powdered activated carbon treatment was also effective at removing 131I. The removal ratio of 131I by granular activated carbon and powdered activated carbon in actual water treatment plants was considered to be around 30% to 40%. In a bench-scale removal test using river water (about 3.5 Bq L-1 of 131I), treated with 10, 25 and 50 mg powdered activity carbon per litre with a 30 minute contact time removed 9%, 36% and 71%, respectively. A weak pre-chlorination with a dose of about 0.5 to 1.0 mg L-1 before powdered activated carbon treatment could enhance the removal to 41%, 59%, 71% for the same powdered activated carbon doses described above. 60 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 3.2 (continued) Radioactive caesium (134Cs and 137Cs) It was found that if radioactive caesium in the water treatment plant existed mainly as particulate form, it is selectively adsorbed on and into some types of soil particles and subsequently removed by particle separation processes including coagulation and flocculation, sedimentation and sand filtration. About 1.5 months after the Fukushima Daiichi accident, removal of 134Cs and 137Cs in a water treatment plant was examined. Levels of 134Cs and 137Cs in raw water were 5.6 and 6.4 Bq L-1 and those after coagulation and sedimentation processes were below the detection limits (which were 0.50 and 0.83 Bq L-1, respectively). These results suggested a reduction in concentration of particulate radioactive caesium of up to a factor of 10. In a bench-scale coagulation test using river water, in which 134Cs and 137Cs concentrations were 5.6 and 6.4 Bq L-1 and turbidity was 51 degrees (approximately 35-41 Nephelometric Turbidity Units), the removal of 134Cs and 137Cs was 94% and 95%, respectively, confirming the high removal of the particulate form (Kosaka et al., 2012). In contrast, radioactive caesium in dissolved ion form cannot be removed. Removal of the ion forms of 134Cs and 137Cs by coagulation, sedimentation and sand filtration in two water treatment plants were measured in October 2012, about 1.5 years after the accident. Levels of 137Cs in dissolved ion form in two raw waters were 0.005 and 0.010 Bq L-1 and those in treated water were 0.005 and 0.011 Bq L-1 (Ohno et al., 2013). The evidence that conventional coagulation and sand filtration processes are not effective to remove radioactive caesium in ion form was further observed in bench-scale tests using contaminated pond water from the reactor site. Levels of 134Cs and 137Cs in the pond water were 9.8 and 11.0 Bq L-1, respectively, and turbidity was 0.3 degrees (approximately 0.2–0.3 NTU). Removal of 134Cs and 137Cs by this coagulation test was only 5% and 6%, respectively. (Kosaka et al., 2012) These results suggested the particle separation processes are very effective in removing the particulate form of radioactive caesium but they do not remove radioactive caesium in dissolved ion form. As a potential effective method for removal of dissolved ion radioactive caesium, addition of soil particle was suggested. In a bench scale test, the addition of 200 mg L-1 of local soil of which the diameter was sieved to 25–75 µm to the dechlorinated tap water (0.1 µg L-1 of 133Cs was added) and stirred for 30 minutes. Using this method, 50% of 133Cs originally in a dissolved form was removed (Tampo et al., 2016). . 61MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N CHA P T e R 3 S U P POR T I N G I N FO RMAT I ON 3.3 IF RADIONUCLIDES ARE REMOVED FROM DRINKING-WATER BY TREATMENT, WHERE DO THEY END UP IN THE TREATMENT PROCESS? COULD THERE BE WASTES FROM WATER TREATMENT PROCESSES THAT NEED TO BE HANDLED AS RADIOACTIVE WASTE ? If radionuclides are removed from water during its treatment, they will end up in the waste products resulting from the treatment processes. For traditional coagulation, sedimentation and filtrations processes, the main waste products will be sludge (from coagulation) and filter media (e.g. sand) from filtration. The production of sludge from the coagulation process is a concentration mechanism, as typically the amount of sludge produced is small compared to the throughput of the water being treated. The amount of sludge depends on the quality of the source water and its level of turbidity, higher levels of turbidity leading to more sludge per litre of water treated. Sludge will also be produced from the backwashing of filters. For example, in a study of radiologically-residual wastes from domestic water treatment in southeast Queensland, Australia, the sludge produced per million litres of treated surface water ranged from 0–46 kg with a mean of 14 kg per million litres of water (Kleinschmidt & Akber, 2008). The authors state that this is consistent with reports from other countries and give comparison values for Germany and the USA. For water treatment plants with a high throughput of water, relatively more sludge will be produced. Information Box 3.3 gives an example of measurements made in sludge in a non-emergency situation. ? 62 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER The accumulation of radionuclides in filter beds, for example sand and activated carbon, is also a concentration mechanism, as the filter beds will accumulate radionuclides over the period that water passes through them and the activity concentration per mass of filter material will increase over time. The less frequent the replenishment of filter bed media, the higher the concentrations will become. The radionuclides removed by filtration will be associated with a very large mass of filter media and the activity concentrations of radionuclides per unit mass of filter material are likely to be significantly lower than those in waste sludge. Further information can be found in Brown, Hammond & Wilkins (2008a). Ion exchange and reverse osmosis will also lead to radionuclides accumulating on the ion exchange resin or reverse osmosis membranes, although these can be removed by regeneration. However, this regeneration will lead to radionuclides being discharged to wastewater, which may need to be controlled. There are practical issues with the removal of filter media and filters or replacing ion exchange or reverse osmosis membranes that would need to be considered, including their removal, transportation, replacement and re-commissioning prior to resuming water treatment. It is unlikely, but still possible, that the activity concentrations in the waste materials arising from water treatment will be required to be managed as radioactive waste. However, activity concentrations in waste products, particularly sludge, can be high in the short-term after an emergency (as shown in the examples in Information Box 3.4) and taking measurements in the treatment waste products should be considered if a nuclear or radiological emergency has led to radionuclides entering water sources that are being treated to supply drinking-water. Specialist advice should be sought from the appropriate regulators. Some background information on the management of radioactive waste products from drinking-water treatment can be found in USEPA (2005). The potential health risks to individuals working in water treatment activities should be considered and may need to be controlled, although it is very unlikely that any exposure to the treatment waste materials would pose any significant health risks to people working on water treatment activities. Further information is given in Question 3.4. Information Box 3.3: Example of activity concentrations in waste sludge in a non-emergency situation in Australia At a site in Northern Territory, Australia, groundwater is extracted from boreholes and is stored in tanks prior to distribution leading to settling of sludge (Kleinschmidt Black & Akber, 2011). Average daily water demand from the bore field is 0.35 million litres per day, peaking at 0.63 million litres per day. The concentrations of radium-226 and radium-228 in the groundwater and sludge are as follows: Radium-226 Radium-228 Water (borehole) 1 Bq L-1 0.7 Bq L-1 Sludge (tank waste) 2830 Bq Kg-1 2010 Bq Kg-1 . 63MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N Information Box 3.4: Examples of activity concentrations in waste sludge after emergencies Following the Fukushima Daiichi nuclear power plant accident in Japan Conventional water treatment processes including coagulation, sedimentation and rapid sand filtration are used in Japan. Therefore, after the Fukushima Daiichi nuclear power plant accident, the radioactive caesium concentrated in the waste sludge. Many water treatment plants had to keep the sludge for the first few months after the accident because the concentration of radioactive caesium was very high (> 8000 Bq Kg-1 of sludge). The sludge cannot be disposed of in normal landfill sites and needs to be stored as radioactive waste; a disposal site for the waste sludge was not agreed until about one year after the accident. Following the Chernobyl nuclear power plant accident in the United Kingdom In a drinking-water treatment works in the northwest of England, high activity concentrations were measured in sludge after the Chernobyl accident (Jones & Castle, 1987). Measurements showed that the treatment used (coagulation and filtration) removed ruthenium and radioactive caesium which accumulated in the sludge. After five months, due to dilution of radionuclides in the water sources being treated (and radioactive decay for 131I and 132Te), the activity concentrations in the sludge had significantly decreased. Concentrations in waste sludge (Bg Kg-1) Radionuclide May 1986 October 1986 103Ru 1900 24 131I 900 Not detectable 134Cs 350 17 137Cs 600 24 132Te 900 Not detectable Key: ruthenium-103 (103Ru); iodine-131 (131I); caesium-134 (134Cs); caesium-137 (137Cs), tellurium-132 (132Te) Following the Chernobyl nuclear power plant accident in Germany Activity concentrations were also measured in sludge cake in Berlin after the Chernobyl accident (BMU, 1987; SSK, 1988). While these measurements were at a wastewater treatment works and not a drinking-water treatment facility, they illustrate the rapid decrease in activity concentrations with time after an accident. The highest activity concentrations were measured on 11 May 1986 (two weeks after the accident) after heavy rainfall, which washed contamination from the environment into the sewage system. As observed in the example from the United Kingdom, activity concentrations in processed sludge cake decreased rapidly over a few months. 64 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 3 S U P POR T I N G I N FO RMAT I ON 3.4 WHAT ARE THE HEALTH RISKS TO PEOPLE WORKING IN WATER TREATMENT ACTIVITIES THAT HAVE PROCESSED WATER CONTAINING RADIONUCLIDES ? If there are radionuclides in the water being treated in drinking-water treatment plants, people working on water treatment activities could be exposed to them while they are working on day-to-day tasks or undertaking routine maintenance. The main sources of exposure will be from being in close proximity to, or inadvertently ingesting, radionuclides in treatment waste products, particularly sludge resulting from coagulation and backwashing of filters and filter material. However, it is very unlikely that any exposure to these materials would pose any significant health risks to these workers. Information on the possible exposure pathways from undertaking water treatment activities are described in USEPA (2005) and Brown, Hammond & Wilkins (2008a). Guidance on how to assess the doses to people undertaking treatment activities can also be found in Brown, Hammond & Wilkins (2008a). If there are concerns about exposure to drinking-water industry workers, specialist advice should be sought. The water supply industry may want to assess the potential health risks to people working in water treatment facilities from radiation exposures as part of their emergency planning, so that exposures could be controlled in the short term after a nuclear or radiological emergency, in the unlikely situation that this is necessary. Information Box 3.5 discusses measurements that were taken to assess impact on workers in water treatment facilities. ? . 65MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N Information Box 3.5 Example of potential doses to people working in water treatment plants after an accident in the United Kingdom In a treatment works in the northwest of England, high activity concentrations of caesium-137 were measured in sludge after the Chernobyl accident (see Information Box 3.5 in Question 3.3. Measurements showed that the treatment used (coagulation and filtration) removed ruthenium and radioactive caesium. There was concern at the time that workers may be at risk from intakes of radionuclides from carrying out some activities, such as cleaning out sludge tanks. However, monitoring indicated that doses were very small; also sludge was kept wet, reducing dust which minimized inhalation doses. Further measured activity concentrations in sludge in October 1986 (five months later) confirmed water entering the treatment works had become diluted and activity concentrations in sludge were much lower. Brown, Hammond & Wilkins (2008a) used the measurements made in sludge and default assumptions about working activities and water throughput at the treatment works to estimate conservative doses for a person carrying out all of the day-to-day tasks (doses were not estimated or measured at the time). The estimated doses using the highest measured activity concentrations in sludge were very low (0.03 mSv in a week) and would subsequently have decreased as activity concentrations in sludge became diluted with time (see Information Box 3.4). 66 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 3 S U P POR T I N G I N FO RMAT I ON 3.5 WHAT METHODS CAN BE USED FOR MEASURING RADIONUCLIDES IN DRINKING-WATER SUPPLIES ? The process of identifying individual radionuclides in drinking-water and determining their concentrations is time-consuming and expensive. A practical approach, regularly used for routine surveillance measurements in non-emergency situations, is to use a screening method where the total (or gross) radioactivity present in the form of alpha and beta radiation is initially determined. The gross alpha and gross beta screening methods rely on the detection of emitted alpha or beta particles during the radioactive decay of the radionuclides. The methods are appropriate for most situations in which radionuclides are likely to be found in drinking-water. While gas proportional counters have traditionally been employed for gross alpha and gross beta measurements and continue to be the standard counters used in many laboratories across the world, the use of liquid scintillation counters is increasing. This technique is more suited to undertaking measurements of groundwaters (typically those having high total dissolved solids content) and can be less resource intensive. Liquid scintillation counters are able to measure beta-emitting radionuclides regardless of the energy of their emissions, whereas gas proportional counters are more limited to those with higher beta energies. However, both techniques are suitable for measuring activity concentrations to compare with the gross alpha and gross beta screening levels. Gross beta measurements will include a contribution from potassium-40, which should be subtracted if the gross beta screening level is exceeded (see Questions 1.5.3 and 1.5.4). References for some standard methods for the analysis of gross alpha and gross beta activity concentrations in drinking-water using gas proportional counters are given in Table 9.3 in Chapter 9 of the GDWQ. Gross alpha and gross beta screening methods only give the total activity present due to alpha and beta activity and radionuclide-specific information cannot be obtained. It should be emphasized that the sum of the activities of the radionuclides contributing to the overall activity concentration in drinking-water is very unlikely to agree with the result from the gross measurements, particularly for gross beta measurements. This is because of the difference in the counting techniques employed, together with the associated uncertainties in the measurements. 1 2 3 4 5 6 7 8 9 10 11 12 ? . 67MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N Methods for measuring individual radionuclides When the individual activity concentrations of specific radionuclides are required, the measurement technique depends on the radionuclide and the type of radiation it emits. High-resolution gamma spectrometry is the standard method for quantifying many gamma-emitting natural and artificial radionuclides. It is a non-destructive measurement that can be applied directly to the sample of drinking-water, without any processing of the sample other than putting an aliquot into a suitable container. Hyper Pure Germanium detector systems are the predominant instrumentation for high-resolution gamma spectrometry but may require concentration of samples when dealing with the activity concentrations commonly found in natural waters. High-resolution gamma ray spectrometry is most likely to be the first measurement technique used in the event of a radiological or nuclear emergency. If gamma ray spectrometry is available, direct measurement of individual gamma-emitting radionuclides could be used as a screening method, as many radionuclides emit gamma rays. The measurements of individual radionuclides using this method should be compared with the guidance levels and not the screening levels. However, gamma-ray spectrometry will not detect all radionuclides that could be in drinking-water for non-emergency situations, particularly naturally occurring radionuclides that would be detected via the gross alpha and gross beta methods. To identify and determine the radionuclides that are predominantly pure alpha or beta emitters and produce none or very weak gamma photons, analytical techniques like alpha spectrometry, liquid scintillation counting, and/or other beta counting techniques are required. The measurement techniques often need to be preceded by radiochemical methods to extract the radionuclide into a form that can be measured. Inductively-coupled plasma mass spectrometry (ICP-MS) is a sensitive, efficient and versatile means of elemental analysis for measuring radionuclides in environmental media, including drinking-water. ICP-MS is being increasingly used due to its high sensitivity, as it detects atoms rather than the radioactive emissions associated with radionuclides. This technique is particularly useful for radionuclides with very long radioactive half-lives, for example uranium-234 and uranium-238, as these radionuclides produce a small number of radioactive decays per unit mass of the isotope and are therefore difficult to measure via their radioactive emissions. The measurement of radon in drinking-water is covered in Section 1.6. Measurements should be made using accredited analytical methods, ideally under a recognized quality standard, such as ISO/IEC 17025:2005 (ISO, 2010). ISO/IEC 17025:200513 is for use by laboratories in developing a management system for quality, administrative and technical operations. As well as quality assurance of the measurements made, the standard puts requirements on a laboratory to undertake proficiency tests (internal and external) to ensure the techniques used are valid and consistent results are obtained. The limits of detection of the various analytical methods and measurement techniques depend on a number of factors, mainly the method and equipment used and the counting time. Standards adopted by a country may specify the limit of detection that is required in order to ensure that the radionuclide concentration in the sample can be confidently assessed against the guidance level (or national standard), taking into account the uncertainties of the measurement. (see Information Box 3.6 for an example) The main features of the different measurement methods are summarized in Table 3.3. Some comparative information is expressed in relative terms and not absolute values, which will be situation specific. References for analytical methods for specific radionuclides are provided in Annex 6 of the GDWQ. 13 ISO17025:2005 specifies the general requirements for the competence of testing and calibration laboratories, including sampling. 68 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Information Box 3.6: Required limits of detection for analytical methods used for measuring radionuclides in the Euratom Drinking-Water Directive As an example, the Euratom Drinking-Water Directive (EC, 2013) gives limits of detection that should be achieved for the analytical methods used for measuring individual radionuclides. Typically, these are about a factor of 10 lower than the derived concentrations (equivalent to the guidance levels in the GDWQ). For gross alpha and gross beta activity concentrations, the limits of detection required are 40% of the relevant screening values (EC, 2013). . 69MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 3. S U P P O R T IN G IN FO R M A T IO N Table 3.3. Main features of the different methods to measure radionuclides in drinking-water Feature Analytical technique Comments Gross alpha/beta ICP‑MS Gamma spectrometry (high resolution) Beta counting Alpha counting General Screening method – total alpha emitting- a n d t o t a l b e t a emitting-radionuclides. Contribution of some radionucl ides wi l l not be included (see Question 1.4.3). Effective for radionuclides with long half-lives. Particularly useful for 234U, 238U. Use for gamma-emitting radionuclides e.g. 134Cs, 137Cs, 131I, 241Am. Will not detect many naturally occurring radionuclides likely to be found in drinking-water, e.g. 234U, 238U, 210Po. 226Ra and 228Ra can be detected with low-energy detectors and assuming equilibrium with other radionuclides can be established. In the case of 226Ra, it has to be ensured that no radon is lost from the sample. Low-resolution spectrom- etry e.g. NaI detectors can be used for screening in emergency situations. Accurate measurement of radionuclides that are predominantly beta emitters, e.g. 90Sr, 3H, 14C. Accurate measurement of radionuclides that are predominantly alpha emitters, e.g. 239Pu, 210Po, 210Pb (via 210Po). Low-resolution gamma ray spectrometry can be used as a screening method following an emergency, e.g. using NaI detectors. Provides broad indication of the activity concentration in the sample but not, in general, specif ic radionuclide information. Speed (elapsed time) Hours–few days (depending on sample preparation time). Hours Hours Days–weeks Days–weeks Standard methods. Rapid methods may be available but these are likely to af- fect the limits of detection achievable. 70 . M A N A G E M E N T O F R A D IO A C T IV IT Y IN D R IN K IN G -W A T E R Feature Analytical technique Comments Gross alpha/beta ICP‑MS Gamma spectrometry (high resolution) Beta counting Alpha counting Preparation of sample/ sample size Sample is evaporated onto a counting disc for gas proportional counters. Concentration of sample for liquid scintillation counters as very small sample size counted (10–15 ml). Measurement is made directly on sample of dr ink ing-water. This enables further analyses to be carried out on the same sample without any degradation of performance. Measurement can be made directly on sample of drinking-water. This enables further analyses to be carried out on the same sample without any degradation of performance. However, sensitivity can be a problem especially for the radionuclide concentrations commonly found in drinking-water in non-emergency situations and therefore some pre- concentration of sample may be required. Complex chemistry to extract radionuclide before measurement. Complex chemistry to extract radionuclide before measurement. High salinity of the water sample can adversely affect the gross alpha measurement due to the shielding effect of the total dissolved solids on the emission and counting of the alpha particles. Limits of detection High Low compared to other methods for measuring individual radionuclides. Higher than gross beta and gross alpha meas- urement techniques. Low compared to gamma spectrometry. Low compared to gamma spectrometry. Training level Medium–high Medium Medium–high High High Gamma counting needs medium training for interpretation of results, low training for sample preparation Likely sample throughput High High High–medium Low Low Duration of overall measurement depends on limit of detection required (based on requirement of low levels of detection for concentrat ions expected in non- emergency situations). Cost per sample Low Low Low High High Excludes purchase of equipment. Relative cost of equipment Medium High High Medium High Key: uranium-234 (234U); uranium-238 (238U); caesium-134 (134Cs); caesium-137 (137Cs); iodine-131 (131I); americium-241 (241Am); polonium-210 (210Po); radium-226 (226Ra); radium-228 (228Ra); strontium-90 (90Sr); tritium (3H); carbon-14 (14C); plutonium-239 (239Pu);lead-210 (210Pb) and sodium iodine (NaI). . 71 M A N A G E M E N T O F R A D IO A C T IV IT Y IN D R IN K IN G -W A T E R Chapter 3. SUPPORTING INFORMATION Additional information for emergency situations In addition to high-resolution gamma ray spectrometry, low-resolution gamma ray spectrometry can be used as a screening method following an emergency, for example using sodium iodine (NaI) detectors. They provide a quick screening measurement that gives a broad indication of the activity concentration in the sample but do not provide specific radionuclide information, unless the gamma-emitting radionuclides are known and can be easily distinguished from each other. In emergency situations, the activity concentrations in water are likely to be much higher than those in non-emergency situations; and higher limits of detection can be accepted for the analytical techniques used. This means that it may be possible to obtain a measurement result more rapidly by reducing the sample preparation time and the counting time for some radionuclides. These rapid methods need to be practiced as part of emergency preparedness, as they will not be routinely used by laboratories and it will be necessary to adapt standard analytical techniques very quickly to respond rapidly to an emergency situation. Some radionuclides, for example strontium-90, will still require radiochemical methods to extract the radionuclide into a form that can be measured. If a high-resolution gamma ray spectrometry capability is available within a country following an emergency situation and the radionuclides of importance are measurable by gamma ray spectrometry, for example caesium-137 and caesium-134, it may be preferable to continue to use gamma ray spectrometry when the situation returns to a non-emergency situation, rather than use the gross alpha and gross beta screening methods (see Information Box 3.7 for an example of this). Information Box 3.7: Example of using gamma spectrometry rather than gross alpha and gross beta screening methods in Japan Japan developed an extensive gamma ray spectrometry capability after the Fukushima Daiichi nuclear power plant accident and has continued to use this to measure radionuclides in drinking-water. An automatic high- resolution gamma spectrometry and measurement system has been introduced at the treatment works where the evacuation order was lifted in 2015. This instrument can automatically quantify the activity concentration of caesium-134 and caesium-137 in treated drinking-water every hour. 72 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CASE STUDIES Chapter 4 CHA P T e R 4 C A S e S T UD I e S 4.1 BRAZIL Background In some Brazilian areas with high levels of naturally occurring radiation, radionuclide activity concentration in groundwater may exceed the WHO guidance levels and the individual dose criterion (IDC) of 0.1 mSv y-1 (WHO, 2017a). One example of this situation occurred in the municipality of Caetité, located in the northeast region of Bahia in Brazil. Caetité contains several uranium anomalies (uranium occurrence above background); 36 anomalies have been mapped so far, spread over an area of 1200 km2. Since 2000, an uranium mining and milling industry has been exploiting one of these radioactive anomalies in the region and environmental monitoring programmes have been conducted since 1989. High uranium concentration in groundwater had been reported for some wells even before the industry started operating in the region. Although Caetité´s population is only about 50 000 inhabitants, 40% of the population lives in rural areas where most of these anomalies occur and groundwater supply is the main source of potable water. In 2008, nongovernmental organizations blamed the uranium industry for groundwater contamination as measurements of gross alpha and gross beta activity performed in some water wells in the region exceeded the WHO screening level based on an IDC of 0.1 mSv y-1. As a consequence, these wells were closed by the local authority until further investigations were done. This situation became the centre of a debate among nongovernmental organizations, the uranium industry, the Ministry of Health (MoH) and the Brazilian Nuclear Energy Commission. The Brazilian Nuclear Energy Commission argued that: i) interpretation and applicability of WHO GDWQ screening levels was misleading; ii) measurements of individual radionuclide concentrations should be performed before taking any decision; iii) high radionuclide concentrations in groundwater have been reported for these wells even before the uranium industry started operating in the region; and iv) the decision of closing the wells was doing more harm than benefit, since they were the most important source of potable water for this rural population. 74 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Regulatory framework and responsibilities for drinking-water In Brazil, the Ministry of Health is responsible for the regulation of microbiological, chemical and radiological contaminants in drinking-water supplies through Resolution MS 2914/2011 (Ministry of Health Brazil, 2011). This resolution requires that every water supply must monitor gross alpha and gross beta activity against the screening levels of 0.5 Bq L-1 and 1.0 Bq L-1, respectively. If the screening levels are exceeded, the concentration of individual radionuclides should be determined and compared with a maximum allowed value for radium-226 (1.0 Bq L-1) and radium-228 (0.1 Bq L-1). The resolution also states that, under the Brazilian Nuclear Energy Commission's requirement, other radionuclides should be investigated. In Brazil, there are three types of water supply systems: 1. large water system supplies with a distribution network operated by water concessionaires in each city or region; 2. an alternative collective water supply system, which includes surface or groundwater collection without a distribution network; 3. an individual water supply system, which usually uses groundwater collection to serve only one family and relatives. While the first two systems are under regulatory control, individual water supply systems are not. The responsible authorities for controlling drinking-water quality in the first two systems submit the monitoring results regarding radionuclides in drinking-water to the public health municipality authority every six months. Description of the situation and response After the complaints made in 2008 by non-governmental organizations, six wells were closed. Unfortunately, the government was not able to maintain the drinking-water supply to the affected communities, which had a great social impact on these communities (e.g. population had to walk long distances to obtain water from other sources). Radiation doses were estimated based on measurements of individual radionuclide concentrations by the Brazilian Nuclear Energy Commission. Several water wells from 10 villages were monitored, and estimated mean doses were in the range of 0.07 to 0.5 mSv y-1. Two wells located in one of these villages were closed as the natural uranium concentrations were above the WHO guideline value for uranium toxicity in drinking-water (30 µg L-1). The Brazilian Nuclear Energy Commission jointly with the Municipality Health Office released a public notice providing a comprehensive review of the situation, explaining that although the estimated dose for some water wells exceeded the WHO IDC of 0.1 mSv y-1, the dose was still below the International BSS reference level of 1 mSv y-1 (IAEA, 2014) and cannot be seen as unsafe for consumption. The purpose of this public notice was to provide technical support to the Municipality Health Office to enable it to reopen the closed wells where the annual doses were above 0.1 mSv y-1 but below the reference level of 1 mSv y-1. Radionuclide monitoring should continue to be carried out and doses should be kept as low as reasonably achievable using a reference level of 1 mSv y-1. The need to review the Brazilian criteria/standards used for radionuclides in drinking-water became quite evident after these events. In order to discuss these events and propose a revision of the national legislation on radioactivity in drinking- water, the Institute of Radiation Protection and Dosimetry (IRD) from the Brazilian Nuclear Energy Commission organized a symposium on water quality and radioactivity. The purpose of this symposium was to join the national regulators, water supply companies, analytics service companies and research institutes involved in drinking-water quality along with representatives of WHO and IAEA to discuss several aspects of radioactivity in drinking-water regulation including the international recommendations, mainly the role of the WHO IDC of 0.1 mSv y-1 and the 1 mSv y-1 reference level in the International BSS. The lack of a clear communication programme with the interested parties had led to new stressful events in 2010 and 2015, such as other complaints of water in wells exceeding the gross alpha and gross beta screening levels and the WHO IDC of 0.1 mSv y-1, resulting again in the shutdown of these wells. . 75MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S Outcome Based on the discussions during the National Symposium on Water Quality and Radioactivity, a working group from the Brazilian Nuclear Energy Commission was established to revise the radiological section of the Brazilian standards for drinking-water. This working group proposed that the Ministry of Health adopt the following criteria for radiological aspects of drinking-water. • Every water supply has to be screened for gross alpha and gross beta activity (screening levels of 0.5 Bq L-1 and 1 Bq L-1, respectively). • If the gross beta activity screening levels are exceeded, the contribution of potassium-40 should be subtracted. • If gross alpha and gross beta activity screening levels (after potassium-40 subtraction) are exceeded, a new sample should be collected and analysed. • If the new gross alpha and gross beta activity levels remain above the screening levels, these results should be forwarded to the Brazilian Nuclear Energy Commission with information about the sampling location and type of water supply (surface or groundwater). • The Brazilian Nuclear Energy Commission should determine which natural or artificial radionuclides have to be investigated in these samples and also request additional information about the water supply. • Results for radionuclide-specific measurements should be forwarded to the Brazilian Nuclear Energy Commission to estimate the total dose due to water ingestion and evaluate if the water is safe for consumption. • The outcome of this evaluation may indicate that no action is required if total doses are below the reference level of 1 mSv y-1, especially in situations where the IDC of 0.1 mSv y-1 is not a practically achievable standard. The National Standard for Water Quality (Resolution MS 194/2011) is under revision to incorporate these new criteria proposed by the working group. Nevertheless, as no effective communication programme has been established so far between the government agencies and the affected community as well as with the nongovernmental organizations, this community is still vulnerable to new events of this nature. Four lessons were learned from these events in Caetité, Brazil. 1. The criteria adopted for managing radioactivity in drinking-water must be consistent among the different regulatory authorities. 2. Exceeding the screening levels or IDC does not necessarily mean that water is unsafe for drinking. It would be useful to provide further guidance/explanations to policy-makers and water suppliers on how to interpret and use the criteria, as these were misinterpreted in this case. 3. Coordination and dialogue among the different regulatory authorities is essential – for example, in this case the Brazilian Nuclear Energy Commission, the Brazilian Institute of Environment and Renewable Natural Resources, Bahia Institute of Water Management and Climate and Bahia Health Department. 4. Risk Communication is a key component of a national plan for management of radionuclides in drinking-water. Both the uranium-mining operator and the regulators need to have a systematic and institutional programme of communication with the community, including public hearings (as specified in the licensing process) to guarantee the involvement of all stakeholders. Having a risk communication programme can reduce this community’s vulnerability to further events of this nature. 76 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER References IAEA (2014). Radiation protection and safety of radiation sources: International Basic Safety Standards. IAEA Safety Standards Series No. GSR Part 3. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/ Pub1578_web-57265295.pdf, accessed 17 October 2017). Ministry of Health Brazil (2011). Resolution 2914, 12 December 2011. Procedimentos de controle e de vigilância da qualidade da água para consumo humano e seu padrão de potabilidade [Procedures for controlling and monitoring water quality for human consumption and potability standard]. Diário Oficial da União; 14 dez. WHO (2017a). Guidelines for drinking-water quality: fourth edition incorporating the first addendum. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/publications/drinking-water-quality-guidelines-4-including- 1st-addendum/en/, accessed 27 November 2017). . 77MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S CHA P T e R 4 C A S e S T UD I e S 4.2 CANADA Background In the Province of Nova Scotia, about 50% of the population rely on groundwater for drinking-water. The presence of elevated levels of naturally occurring uranium in groundwater was identified in 1978. In response to this finding, a provincial uranium task force was formed. Subsequent investigation tested more than 700 water wells for radionuclides during the 1980s. It has become routine in Nova Scotia to test for uranium in drinking-water monitoring programmes. However, most of the other naturally occurring radionuclides were not commonly tested. Drinking-water systems were routinely tested for gross alpha and gross beta activity. Regulatory framework and responsibilities for drinking-water In Canada, the responsibility for making sure drinking-water supplies are safe is shared between the provincial (10 provinces), territorial (three territories), federal and municipal governments. The provincial government is the regulator for all drinking-water supplies. The day-to-day responsibility of providing safe drinking-water to the public generally rests with the authorities in the provinces and territories, while municipalities usually oversee the day-to-day operations of the treatment facilities. The Federal-Provincial-Territorial Committee on Drinking-Water (comprising members from the authorities responsible for drinking-water quality in each jurisdiction) together with Health Canada established the Guidelines for Canadian drinking-water quality (Health Canada, 2009). These guidelines deal with microbiological, chemical and radiological contaminants. They also address concerns with physical characteristics of water, such as taste and odour. Maximum acceptable concentrations for natural and artificial radionuclides are calculated using a reference dose level of 0.1 mSv for 1 year’s consumption of drinking-water, assuming a consumption of 2 litres per day at the maximum acceptable concentrations. 78 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Description of the situation and response In May 2002, during an environmental assessment in which drinking-water was tested for gross alpha and gross beta activity, the gross alpha activity in well water at a school in Hubley, Nova Scotia, exceeded the Canadian screening level of 0.1 Bq L-1 (the screening level effective at that time). Follow-up detailed analysis showed that all naturally occurring radionuclides were below Canadian guideline values, except for lead-210 (210Pb). The Department of Education took extra precautions to ensure that drinking-water was safe for students and staff surrounding the school in Hubley. In a press release on 29 May 2002, the Education Minister said “We take the health and safety of students very seriously, … While we have no reason to believe there are problems at other schools, testing the water is a responsible and precautionary step. We don’t take chances where children are concerned” (Department of Education, 2002). The province’s medical officer of health for the region also said at the first press release that there was no public health risk associated with continuing to drink water with the levels of 210Pb found in the preliminary sample at the school in Hubley. He explained clearly that the preliminary result indicated only that further investigation was necessary. It was announced at the press release that tests had started immediately in 13 schools from St. Margaret’s Bay to Herring Cove for naturally occurring radionuclides (uranium-234, uranium-235, uranium-238, thorium-228, thorium-230, thorium-232, thorium-234, radium-224, radium-226, radium-228, lead-210, polonium-210, bismuth-210, beryllium-7). In response to this discovery, an inter-governmental special well water advisory group was promptly formed and led by the Department of Environment and Labour. A province-wide sampling programme was initiated at public schools, municipal water supplies and registered public water supplies in 2002 and 2003 to determine levels of individual radionuclides and identify areas and geological formations in the province where drinking-water supplies were most likely to have elevated radionuclide levels (Drage, Baweja & Wall, 2005a; Drage, Baweja & Wall, 2005b). The province-wide radiological testing programme took a graded approach. The initial sampling programme of testing drinking-water in 52 schools was conducted in June 2002. Twelve of the schools were found to have levels of 210Pb above Health Canada’s guideline for drinking-water (0.2 Bq L-1). In two of these 12 schools, total uranium was also above Health Canada’s drinking-water guideline (0.02 mg L-1). The test results initiated an expanded testing programme in September 2002 to cover all provincial schools (184 in total). Among the 184 schools, 178 schools had groundwater supplies and six had surface water supplies. Radiological tests were only conducted in schools with groundwater supplies. The results confirmed that 210Pb and total uranium levels commonly exceeded drinking-water guidelines: 16 of 178 (9%) school water wells had elevated 210Pb and three (2%) school water wells had elevated total uranium. Based on the radionuclide levels observed in the province-wide testing programme, it was anticipated that owners of domestic wells and public water supplies would require information on how to treat the drinking-water for 210Pb and uranium. Since water treatment systems for uranium have been commonly used and available, the evaluation of treatment methods for 210Pb was conducted. A literature review indicated that reverse osmosis and ion-exchange treatment systems were likely to be the most practical treatment options for treating 210Pb. A field evaluation programme was initiated at several schools with elevated levels of 210Pb to confirm 210Pb removal efficiencies of these systems. The results from the field evaluation showed that both treatment methods had 210Pb removal efficiencies of less than 29% and were not able to effectively reduce 210Pb levels. However, once activated carbon or aeration was added, removal efficiencies were greatly improved (Drage, Baweja & Wall, 2005b). . 79MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S With aeration to remove radon in water, levels of 210Pb were reduced by more than 90%. This suggested that very little 210Pb was present when the water was first drawn from the well for drinking, and most 210Pb was generated by radon decay in the time between when the water was taken from the well and its analysis. The sampling protocol was modified accordingly, i.e. radon was removed from groundwater samples at the time of sampling by boiling for 10 minutes to eliminate the generation of 210Pb arising from radioactive decay of radon in the drinking-water during the laboratory analysis. All schools originally over the 210Pb guideline were retested with the modified sampling protocol. The final results led to the conclusion that 210Pb was not a significant problem in Nova Scotia, but levels can exceed the guideline value if water containing radon is stored prior to consumption. This new understanding of how to test for 210Pb has provided a valuable lesson for many other jurisdictions in the assessment of 210Pb levels in drinking-water. The 210Pb project raised the potential issue of radon in drinking-water and the more important question of exposure to radon in indoor air resulting from the use of water containing radon. As a precautionary measure, indoor radon tests were conducted in the summer of 2004 as an extension of the work done to address radionuclides in drinking-water in schools. Results showed levels below the Canadian guidelines for radon in air at schools. Outcome The 210Pb project earned credibility by acknowledging challenges proactively, rather than trying to downplay concerns. Communications were incredibly important to the project, especially since the issue was initially discovered in schools. The project team reported frequently, even when results were not yet available; this built trust that the team was being open and honest about the situation. Between 2002 and 2004, there were a total of 10 press releases issued, first by the education ministry then led by the Department of Environment and Labour. In all the press releases, the effective communicator was the medical officer of health for the region. At the last press release on 21 September 2004 (Department of Environment and Labour, 2004), it was announced that the Department of Environment and Labour had set up a toll- free telephone number for information about radionuclides in well water and radon. References Department of Education (2002). Province to test school water in Sir John A Vicinity. Press release, 29 May 2002 (http:// novascotia.ca/news/release/?id=20020530002, accessed 18 October 2017). Department of Environment and Labour (2004). Majority of schools come off bottled water. Press release, 21 September 2004 (http://novascotia.ca/news/release/?id=20040921001, accessed 18 October 2017). Drage J, Baweja A & Wall P (2005a). Naturally occurring radionuclides in ground water in Nova Scotia • Part 1. Canadian Radiation Protection Association Bulletin. 26(3):15–21. Drage J, Baweja A & Wall P (2005b). Naturally occurring radionuclides in ground water in Nova Scotia • Part 2. Canadian Radiation Protection Association Bulletin. 26(4):13–22. Health Canada (2009). Guidelines for Canadian drinking-water quality. guideline technical document: radiological parameters. Ottawa: Health Canada (http://healthycanadians.gc.ca/publications/healthy-living-vie-saine/water-radiological- radiologique-eau/index-eng.php, accessed 19 October 2017). 80 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CHA P T e R 4 C A S e S T UD I e S 4.3 JORDAN Background Jordan14 is a severely water stressed country. Groundwater constitutes 80% of the domestic water supplied, a source that is already exploited by 160% above safe yields. To augment the water supply, especially in high-demand areas, the Disi Water Conveyance Project was developed between 2005 and 2009. The Disi Water Conveyance Project is a “build-operate-transfer” project15 that extracts 100 million m3 y-1 of fossil groundwater from 55 wells drilled in the Ram Aquifer System in the southern desert of Jordan. This water is conveyed to the capital Amman (4 million inhabitants) via a conveyer pipe that is 1.7 m in diameter and 320 km in length. In June 2013, The Disi Water Conveyance Project started supplying the capital Amman with 70 million m3 y-1 in an emergency mode due to the high demand following the influx of 1.3 million Syrian refugees. In January 2014, the Disi Water Conveyance Project started supplying Amman with its full capacity of 100 m3 y-1 of water. The Ram aquifer water (Disi) is blended with sufficient amounts of surface water from sustainable sources (Figure 4.1). An extension is now under implementation during 2017–2018, which will ultimately serve 75% of the total population of Jordan and will fulfil increased demand in the north of the country. 14 A significant portion of this case study comes from El-Naser et al. (2016). 15 Build-operate-transfer projects are explained at: https://ppp.worldbank.org/public-private-partnership/agreements/concessions-bots-dbos#overview. . 81MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Regulatory framework and responsibilities for drinking-water In Jordan, the Ministry of Health is the regulator for drinking-water quality. The responsibility for ensuring the safety of drinking-water supplied to the public is shared between the Water Authority of Jordan, which is the water provider and the Ministry of Health. The Ministry of Health is responsible for surveillance activities, from catchment to consumer. The Higher Committee for Water Quality plays an advisory role on water quality-related issues. This committee is chaired by a representative from academia and includes membership from relevant ministries. It develops water quality management guidelines and manuals and provides recommendations to be considered in the revisions of the water quality standards. Through a national team of experts from different organizations including the Ministry of Health, the Jordan Standards & Metrology Organization develops and reviews the national Jordanian standards including the drinking-water standard JS286, which specifies the limits, reference levels, sampling frequencies and points along the supply chain for the physical, chemical, radiological and microbiological parameters in drinking-water. It also defines the actions and intervention needed in case of violation or exceedance for any of the listed parameters. The latest edition of the JS286 was issued in 2015 and has been effective since 1 May 2016. For radiological water quality management, the Disi Water Conveyance Project company developed Part 2 of the Environmental and Social Management Plan (ESMP2), to be implemented by the Water Authority of Jordan. The ESMP2 defines the water quality compliance requirements for monitoring and blending that reflect the GDWQ and the Jordanian Drinking-Water Standard Requirements. The Water Authority of Jordan and the Ministry of Health jointly developed a protocol containing a detailed monitoring programme and management actions required to ensure that blended water supplied to customers always complies with the JS286 and the ESMP2 requirements. Description of the situation and response Water quality investigations on the groundwater of the Ram aquifer between 2001 and 2009 revealed elevated gross alpha and gross beta concentrations above the screening levels. The concentrations were dominated by naturally occurring radium-226 (226Ra) and radium-228 (228Ra). The average dose of the Ram aquifer was between 0.65–0.75 mSv y-1 with 70–85% of the dose due to 228Ra. The Government of Jordan accordingly requested technical and normative guidance from WHO on i) revising the reference level in the Jordanian national standard for radioactivity in drinking-water and ii) the suggested national intervention and management actions in case the reference levels were exceeded. In 2008, The Jordanian reference level in the drinking-water standard was raised from 0.1 to 0.5 mSv y-1 after consideration of the guidance from WHO in the GDWQ and careful review of the local environmental, social and economic conditions. The new reference level was justified based on the assessment that the potential health risks are tolerable and the net health benefits of the provision of adequate water outweigh the potential health risks due to radionuclide content in water. 82 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Between 2005 and 2012, the Water Authority of Jordan considered management options to secure safe water that meets the requirements of the revised national drinking-water standards; for each of the alternatives a feasibility study was performed according to a pilot scale design. After considering remediation of the full yield of the Disi Water Conveyance Project of 100 million m3 y-1, via environmental and cost–benefit analysis, it was decided that the most practical and sustainable option for Jordan was blending the Ram aquifer water (Disi) with available low radioactivity surface water sources that are sustainable in the following amounts: 90 million m3 y-1 from Zai and 45 million m3 y-1 from Zara-Ma’en drinking-water supply systems. For small communities supplied by single high-radioactivity wells where no water is available for blending, different treatment options at the wellhead are explored after approvals are obtained from the Ministry of Health. The treatment options are reverse osmosis and resin ion exchange, which are both being used in small-scale pilot projects. Figure 4.1 shows the entire system of sampling points from the source to the point of consumption. The Water Authority of Jordan is requested to provide quarterly progress reports to the Disi Water Conveyance Project company. Figure 4.1. A simplistic schematic of the Disi-Mudawarra conveyance system to Amman Dubaydib well field; 55 boreholes Reservoir (A) (Dabuk) Reservoir B1 (Abu Alanda 1) Marqab Reservoir Dabuk booster (SA-B) Dabuk customer meter (SA or SC) Marqab customer meter (SB or SC) Reservoir B2 (Abu Alanda 2) Turn-outs (TO) Output B Output A Blending water A (BA) North Amman Distribution Network from Dabuk – Supply A (SA or C) South Amman Distribution Network from B2 or (Marqab) Supply B (SB or SC) Blending water B (BB) Combined well field output (CO) well Source: Reproduced from Journal of Water and Health volume 14, issue number 3, pages 528–48, with permission from the copyright holders, IWA Publishing. The sampling and analysis programme was developed by the Water Authority of Jordan and approved by the Ministry of Health for the radioactive parameters of concern (monthly for gross alpha, gross beta, radon-222 (222Rn), 226Ra, 228Ra, lead-210 (210Pb) and annually for radium-224 (224Ra). This was done to ensure that the JS286 and the ESMP2 for radiological parameters could be met with the following frequencies. • Quarterly grab samples from each of the 55 wells constituting the Disi Water Conveyance Project well field to assess trends of radioactivity levels over time. The frequency will be reduced to once per year after two years of operation. . 83MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S • Monthly grab sample from the combined water of the 55 wells at the header tank in the south of Jordan before the water is admitted to the main 320 km conveyer pipe. • Monthly composite samples of the Disi water before blending at the two delivery points in Amman (Dabuk reservoir in the north of Amman and Abu Alanda reservoir in the south of Amman). • Yearly monitoring of the blending waters from Zara-Ma’en and Zai treatment plants (historical results for gross alpha, gross beta, 226Ra and 228Ra are consistently below the analytical detection limits). • Monthly composite samples of the drinking-water after blending measured at the outlets of the main reservoirs in Amman. • Monthly composite samples from public reservoirs to represent the water supplied to consumers in the different distribution zones in Amman. The Water Authority of Jordan follows the approach recommended in the GDWQ (Figure 9.2; WHO, 2017), assessing against the screening and guidance levels for radionuclides in drinking-water and sending monthly reports (or whenever an emergency arises) of the results to the Ministry of Health. The interventions taken by the Water Authority of Jordan and the Ministry of Health are in accordance with the approved national protocol and comply with the JS286 and the ESMP2 requirements. The staged approach to intervention is illustrated in Table 4.1. Table 4.1. Intervention protocol to be followed in Jordan after radionuclide monitoring in drinking-water Dose unit mSv y-1 – 0.5 is the reference level < 0.45: No action; maintain routine monitoring ≥ 0.45: Red flag value; be vigilant > 0.5 – < 1.0: Investigate to lower the dose while maintaining use of water supply ≥ 1.0: This is the action limit where water supply is stopped and issue addressed The Water Authority of Jordan is required to immediately notify (red flag notification) the Ministry of Health and the Disi Water Conveyance Project company in the event that the blended water output exceeds the annual dose of 0.45 mSv. The Water Authority of Jordan must carry out progressive sampling of the boreholes within three months after notification is issued, to identify and mitigate the problem, and inform the Ministry of Health and Disi Water Conveyance Project company when corrective actions are taken. The protocol specifies that the number of days during which blending stops shall not exceed 46 days per calendar year; this is based on historical data and calculations to ensure that the requirements in the JS286 and the ESMP2 are complied with, taking into account that the two surface water sources used for blending are subject to closure during floods. Outcomes In managing radioactivity in the water of the Disi Water Conveyance Project, Jordan developed, adopted and implemented a solution compatible with the national conditions after guidance and support from WHO. The outcome of this project is that the water is now more frequently monitored, risk is assessed and the water is managed more effectively overall. Quarterly results of gross alpha, gross beta, 226Ra, 228Ra, 222Rn and 210Pb from each of the 55 wells constituting the Disi Water Conveyance Project well field have remained constant since the start of operations in 2013. The activity concentrations of 210Pb have been consistently below the detection limit while 222Rn activity concentrations have been fairly low. 84 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER The annual radiological dose along the drinking-water supply chain (after blending, distribution and delivery to the point of consumption) is around 0.40 mSv y-1. This dose is below the red flag value of 0.45 mSv y-1 and the JS286 reference level of 0.5 mSv y-1. To gain public trust awareness campaigns were organized and the activities related to the risk assessment, development of the Jordanian drinking-water standard (and reference level) and management of the Disi Water Conveyance Project were conducted in a transparent manner. Although the Jordanian authorities have assessed that blending is effective and the water supplied to consumers is safe, there are still areas that need to be addressed: • Assess the long-term health impacts of consuming drinking-water meeting the national standard limit of 0.5 mSv y-1 on infants and children. • Evaluate the health impact of short lived radionuclides like 224Ra, especially when considering small community water supply wells in the south of Jordan where the time between abstraction and consumption is short. References El-Naser HK, Smith B, Kilani S, Abdeldin I, Howarth B, Saleh B (2016). Blending as the best compliance option for the management of radioactivity in drinking-water supplied from the deep sandstone aquifer in Southern Jordan. J Water Health. 14(3):528–48. . 85MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S CHA P T e R 4 C A S e S T UD I e S 4.4 SWEDEN Background In Sweden, where uranium-rich geology prevails, high concentrations of naturally occurring radionuclides are expected in drinking-water extracted from the ground. This may particularly be an issue in drinking-water coming from bedrock aquifers. Naturally occurring radionuclides from the uranium-238 decay series are of principal interest. Radon is the most studied radionuclide but awareness of uranium in drinking-water is increasing. Regarding the occurrence of other radionuclides in that series, such as polonium-210 (210Po) and lead-210 (210Pb), knowledge is limited. The occurrence of radionuclides from the thorium-232 decay chain in drinking-water have not been studied despite the fact that the concentration of thorium is three times higher than that of uranium in soils and bedrock (SGU, 2016). There are about 2000–3000 public water works in operation, using groundwater as a source of drinking-water. Public water works supplying large volumes of water are operated principally by municipalities but there exist a large number of private companies supplying drinking-water on smaller scales. Concentrations of radionuclides in public water supplies are generally low. In addition to public water works, there are about 260 000 drilled wells and 140 000 dug wells that are used on a permanent basis in Sweden. The number of drilled wells increases by approximately 5000 annually. About 1.2 million people obtain their daily water supply from these private wells. Information about the concentration of radionuclides in drinking-water from private wells is insufficient but the few studies that have been performed over the years (Salih, 2003; Skeppström, 2005; Ek et al., 2008) provide insight into the extent of the problem. The concentrations of radionuclides in many private drilled wells are significant and in some cases very high. Regulatory limits for radioactivity in drinking-water In Sweden, the National Food Agency issues regulations to ensure safe drinking-water to the population. The regulations include criteria for microbiological, chemical and radiological contaminants in drinking-water and are applicable to public water supplies. The National Food Agency is a central authority and does not perform any supervision over water treatment facilities. This responsibility is instead assumed by municipalities. 86 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Since Sweden is a member state of the European Union, the criteria used for radionuclides in drinking-water are in agreement with the requirements laid down in the Euratom Drinking-Water Directive (EC, 2013). This directive aims to protect the health of the general public with regard to radioactive substances in water intended for human consumption. For public water supplies, Sweden has set a regulatory limit of 100 Bq L-1 for radon. Remediation measures are required if radon concentrations in drinking-water exceed that limit. For uranium, a concentration of 30 µg L-1 should not be exceeded and this recommendation is principally used to protect against the chemical toxicity of the metal. For drinking-water extracted from groundwater, it has been mandatory since November 2015 to screen for gross alpha and gross beta activities. The screening level is set as 0.1 Bq L-1 and 1 Bq L-1 for gross alpha and gross beta activity, respectively. Specific radionuclide analyses are required if the screening levels are exceeded. The screening and parametric values (excluding radon and short-lived radon decay products) are based on an indicative dose of 0.1 mSv y-1 16, assuming a consumption of 730 litres per year. The indicative dose is a binding limit in Sweden. For private wells, there exist two recommendations for radioactivity in drinking-water. Remediation measures are recommended if the concentration of radon exceeds 1000 Bq L-1 and for uranium, the concentration should not exceed 30 µg L-1. Radioactivity in drinking-water from public water works The only radioactive element that has routinely been analysed since the late 1990s in Sweden is radon. Requirements to control indicative dose as stipulated by the Euratom Drinking-Water Directive (EC, 2013) (which superseded Council Directive 98/83/EC) were enforced in Swedish regulations in 2003 but were poorly abided to, due to lack of guidelines on how the requirements should be implemented. The Swedish Radiation Safety Authority and the National Food Agency initiated a project in 2004 with the aim of getting an overview of the situation in Swedish drinking-water (Falk et al., 2004). The project targeted public water supplies where groundwater (both bedrock aquifers and soil aquifers) was used as a source of drinking-water and 265 municipalities were given the opportunity to provide water samples. The project led to the collection of 256 samples of treated water from water works supplying large volumes of drinking- water. Gross alpha and gross beta measurements were performed on all water samples as a screening strategy. Radium-226 (226Ra) was also determined in all water samples. For the majority of the water samples (~80%), gross beta concentrations were below the detection limit. The screening level of 1 Bq L-1 was exceeded in only 21 water samples but no radionuclide-specific analysis was performed to determine which radionuclides contributed to the gross beta activity. Regarding gross alpha activity, 65% of water samples were below the detection limit; the screening level of 0.1 Bq L-1 for gross alpha activity was exceeded in 40 water samples. For the calculation of indicative dose, all alpha activity was assumed to come from uranium when no activity from 226Ra was detected. In samples where 226Ra was found to occur, the activity from uranium was deduced from the difference between the gross alpha activity and activity from 226Ra. The concentration of 226Ra in almost all samples was below the detection limit. Drinking-water from only two water works (barely 1% of the studied water works) had an indicative dose exceeding 0.1 mSv y-1. The conclusion drawn from that study (Falk et al., 2004) was that the concentrations of radionuclides in drinking-water from public water works did not usually lead to the exceedance of the indicative dose and hence proved no risk to health. It is worth noting that only 256 water works out of a total of approximately 3000 were studied in that project. However, since the implementation of the Euratom Drinking-Water Directive (EC, 2013) in November 2015, all relevant water works are gradually analysing and evaluating the quality of drinking-water with regard to radioactive substances. The National Food Agency has also created a database at the national level to collect all measurement results and other parameters, 16 Similarly, the screening and guidance levels in the GDWQ are based on an IDC of 0.1 mSv per year, where the gross alpha screening value is 0.5 Bq L-1 and the gross beta screening value is 1 Bq L-1. The gross alpha screening value was changed from 0.1 to 0.5 Bq L-1 in the third edition of the GDWQ in 2004. . 87MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S with the aim of evaluating the data. Hence a better picture of the scale of the problem of radioactivity in drinking-water from public water works will be obtained after some years. The regulations for radioactivity in drinking-water together with the infrastructure to follow up measurement data for drinking-water from public water works will be used to ensure that the public is not exposed to high concentrations of radionuclides in drinking-water. The main challenge is instead for those who are not connected to a public water supply but instead obtain their water supplies from private wells. Radioactivity in drinking-water from private wells About 12% of the population in Sweden obtain their drinking-water supply from private wells. In 2001, a mapping project of naturally occurring radionuclides in drinking-water from private wells was launched by the Swedish Radiation Safety Authority in collaboration with the Geological Survey of Sweden. The study, which lasted for five years, had several aims; the main aim was to get an overview of radioactivity in drinking-water in private wells and thereby to make an estimation of the potential radiation dose that certain groups of the population can receive. Two other aims were to study temporal variation and potential correlation that can exist between different radionuclides. Results of temporal variation and correlation are not presented here. The study included 722 drilled wells. Sampling was conducted by the staff at the Geological Survey of Sweden. The large majority of the wells were chosen at random way and the selection was made county-wide, covering a total of 24 counties. Wells were also chosen in areas known to have high concentration of radioactivity in the geological media. Geogenic maps were used and previous studies were reviewed to identify areas of interest. A special area of interest, the Siljan Ring, located in the municipality of Rättvik was studied. This region has a unique geological formation due to the fall of a meteorite about 360 million years ago. Private wells located in that region have very high concentrations of uranium as well as other metals. The approach adopted in that study was screening for gross alpha and gross beta activity prior to any specific radionuclide analysis, with the exception of radon. Exceedance of 0.1 Bq L-1 for gross alpha activity led to the measurement of activity concentration of 226Ra. Activity concentration from uranium (uranium-238 (238U), uranium-234 (234U) and uranium-235 (235U)) was calculated as the difference between gross alpha activity and activity concentration of 226Ra. The activity concentrations of these radionuclides were required for the calculation of indicative dose. The concentration of uranium expressed in µg L-1 was also determined with the aim of comparing the values with the recommendation issued by the authority. Results of mass concentrations of uranium are not presented here. Exceedance of gross beta did not lead to specific analysis of any beta-emitting radionuclide, although concentration of lead-210 (210Pb) was estimated in a few samples, from the beta energy-spectrum. It was assumed that the major contributors to indicative dose were the alpha-emitting radionuclides from the U-238 decay series. Concentration of 226Ra was generally low in drinking-water with a median value of 0.02 Bq L-1 and a maximum of 7.0 Bq L-1. Regarding uranium (238U, 234U, 235U), the median activity concentration was found to be 0.13 Bq L-1 and a maximum of 26.7 Bq L-1 was recorded. Activity concentrations of uranium exceeding the guidance value of 3 Bq L-1 was found in 2% of the studied wells. Radon concentration exceeding 1000 Bq L-1 was measured in 8% of the studied wells, supplying drinking-water to about 60 000 people. The maximum and median concentrations for radon were 66 200 Bq L-1 and 220 Bq L-1, respectively. Calculation of indicative dose based on the activity concentrations of uranium (238U, 234U, 235U) and 226Ra were performed for 620 wells. It was found that 10% of the wells had an indicative dose that exceeded 0.1 mSv y-1. In areas near the Siljan Ring, concentrations of all studied radionuclides in drinking-water were high. Consumption of water from a large 88 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER majority of wells in that area would give a radiation dose exceeding 0.1 mSv y-1. The highest dose calculated (including dose contribution from 210Pb) in that region was 5 mSv y-1. One limitation of the project is that neither 210Pb (except in a few samples from areas near the Siljan Ring) nor 228Ra, were analysed in water samples. These elements can potentially be present in drinking-water in Sweden as shown by previous studies (Salih, 2003). This implies that the radiation dose received by the population consuming drinking-water from private wells could be higher than the dose calculated just from uranium and 226Ra. Another limitation of the project is that 210Po which could potentially be present in some samples had not been investigated. Finally, gross alpha activity was assumed to come from 226Ra and the isotopes of uranium, implying that dose contribution from uranium isotopes might have been overestimated in some cases. Conclusions and response The studies from public water works and private wells highlighted that some private wells are particularly at risk. Where the results showed extreme concentrations of radionuclides (radon concentrations > 1000 Bq L-1 and activity concentration of uranium > 3.0 Bq L-1), the owners of the wells were contacted and informed about the problem. Site visits were also made in the study area near the Siljan Ring, in the municipality of Rättvik, where the highest concentrations of radon and uranium were detected. Health inspectors at the municipality as well as stakeholders at county level were informed about the extent and significance of the problem. This in turn led to further studies and local information campaigns in that region. A follow-up survey showed that many participants who had high concentrations of radon and uranium in their drinking-water took remediation measures after the nationwide mapping project. Aeration techniques for radon and ion exchange filters for uranium were commonly used. The follow-up survey also showed that many private well owners still had limited knowledge on radioactivity in drinking-water despite their participation in the project. This highlighted the need for regular risk communication about radionuclides that occur naturally in the environment. References EC (2013). Council Directive 2013/51/EURATOM laying down requirements for the protection of the health of the general public with regard to radioactive substances in water intended for human consumption. Brussels: European Commission (http://eur-lex.europa.eu/, accessed 19 January 2018). Ek BM, Thunholm B, Östergren I, Falk R, Mjönes M (2008). Naturligt radioaktiva ämnen, arsenik,och andra metaller i dricksvatten från privata brunnar [Naturally occurring radioactive elements, arsenic and other metals in drinking-water from private wells]. SSI-report 2008:15. Stockholm: Swedish Radiation Protection Authority (in Swedish). Falk R, Mjönes L, Appelblad P, Erlandsson B, Hedenberg G, Svensson K (2004). Kartläggning av naturligt radioaktiva ämnen i dricksvatten [A survey of natural radioactivity in drinking-water]. SSI Report 2004:14. Stockholm: Swedish Radiation Protection Authority (in Swedish). Salih IM (2003). Radon in natural waters [dissertation]. Linköping: Linköping University. SGU (2016). Mineralmarknaden, Energimetallerna uran och torium [Market of minerals, fuel facts on uranium and thorium]. Report 2016:2. Uppsala: Geological Survey of Sweden (in Swedish). Skeppström K (2005). Radon in groundwater - influencing factors and prediction methodology for a Swedish environment [thesis]. Stockholm: KTH Royal Institute of Technology. . 89MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S CHA P T e R 4 C A S e S T UD I e S 4.5 JAPAN Background After the 11 March 2011 Great East Japan Earthquake and subsequent tsunami, the Tokyo Electric Power Company’s (TEPCO) Fukushima Daiichi nuclear power plant was severely damaged, resulting in the release of a large amount of radionuclides into the environment in Japan. The dispersion and deposition of these radionuclides was influenced by the prevailing meteorological conditions during the passage of the radioactive cloud, particularly the wind direction and the occurrence of precipitation (e.g. rain, snow). Measures were taken by national authorities to protect people from the consequences of the accident, including the establishment of a 20-km evacuation zone with a 30-km sheltering zone. As the availability of environmental monitoring data increased, other protective actions were implemented to reduce doses in the longer term (WHO, 2012; WHO, 2013). Monitoring of tap water was conducted, both by central and local government and by the water supply utilities. On 16 March 2011, iodine-131 (131I) was first detected in some tap water samples and, beginning on 21 March, restrictions on tap water consumption were applied in a number of villages and cities, including Tokyo (MHLW, 2011a). However, because 131I has a short half-life (~eight days), activity concentrations in drinking-water rapidly decreased; afterwards caesium-134 (134Cs) and caesium-137 (137Cs) were the main radionuclides of concern. The water supplies affected were mostly public supplies from surface water sources. Generally, private water systems were not affected because they principally rely on groundwater as a source. Regulatory framework for drinking-water In Japan, the regulatory authority for drinking-water is the Ministry of Health, Labour and Welfare. The Water Supply Division of the Ministry of Health, Labour and Welfare establishes the drinking-water quality standards and related items. Radioactive substances are not in the category of regulated items, but since the accident, their monitoring in Fukushima and the neighbouring 10 prefectures has been requested by the Ministry of Health, Labour and Welfare. In the case of a 90 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER severe emergency in the future, the Nuclear Regulation Authority or the Ministry of Health, Labour and Welfare will be responsible for any restrictions placed on drinking-water. On 17 March 2011, the Department of Food Safety of the Ministry of Health, Labour and Welfare established provisional regulation values, of radionuclide concentration in domestic food by adopting the guidelines from the Nuclear Safety Commission in Japan, which was reformed into the Nuclear Regulation Authority in September 2012 (in accordance with the Food Sanitation Act, Act No. 233 of 24 December 1947) (MHLW, 2011b). Drinking-water (which includes tap water, well water and bottled water) was included as one of the categories for application of the provisional regulation values. Regulation values were provided for 131I, 134Cs, 137Cs, uranium and the alpha-emitting nuclides of plutonium and other transuranic elements. There were no screening levels such as gross alpha and gross beta activity concentrations put in place. On 19 March 2011, the Water Supply Division of the Ministry of Health, Labour and Welfare established provisional index levels for restriction on tap water intake, which were the same levels as provisional regulation values but, which were provided only for 131I, 134Cs and 137Cs (MHLW, 2011c). The Ministry of Health, Labour and Welfare notified local government authorities and regional water suppliers that tap water contaminated above the provisional regulation values should ideally not be consumed but can be consumed even by infants if an alternative water supply could not be obtained (MHLW, 2011c). The current criterion (for non-emergency situations), which is called “the target level for management of radioactive materials in tap water”, was established on 1 April 2012 (MHLW, 2012), about one year after the Fukushima Daiichi nuclear power plant accident. Description of the situation and response During the period of emergency exposure, Fukushima Prefecture and the other neighbouring 10 prefectures were designated as the main monitoring areas, from which intensive measurement of 131I, 134Cs and 137Cs in tap water was requested by governmental organizations including the Ministry of Health, Labour and Welfare. The population in the area was about 50 million and accounted for 40% of the total population in Japan (about 126 million). Many governmental organizations, research institutions and water supply utilities started working cooperatively on the measurement of source and tap water on a daily basis or more frequently. Individual radionuclides, primarily 131I, 134Cs and 137Cs, were measured using high-purity germanium semiconductor detectors or sodium iodine scintillation counters. All of the measured concentrations of radionuclides in drinking-water were publicly announced via the websites of the Ministry of Health, Labour and Welfare and each water supplier. As a response to the to the emergency situation, on 17 March 2011 provisional regulation values for restriction on drinking- water were established by Department of Food Safety of the Ministry of Health, Labour and Welfare. A provisional regulation value of 300 Bq Kg-1 was established for 131I and 200 Bq Kg-1 for radioactive caesium (the sum of 134Cs and 137Cs). On 19 March 2011, the Water Supply Division of the Ministry of Health, Labour and Welfare announced provisional index levels for restriction on tap water intake, which were the same levels as provisional regulation values but supplied only for 131I and the sum of 134Cs and 137Cs. On 21 March, the Water Supply Division additionally announced that the provisional index level of 131I for infants was 100 Bq Kg-1 (MHLW, 2011d). Restriction on infants’ intake of tap water was requested by 20 water supply utilities, which served a population of about 14 million including the Tokyo metropolitan area, starting on 21 March 2011. The restriction in the Tokyo metropolitan area was only for two days (23 and 24 March) and in other areas was lifted by 1 April 2011 in all water supply utilities except one small-scale water supply in Fukushima Prefecture (supplying Iitate village, which served a population of about 4000) (MHLW, 2011a). The restriction on infants’ intake of tap water was lifted on 10 May 2011 in the water utility supplying . 91MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S water to Iitate village (although the restriction for all other age groups was lifted on 2 April 2011). No water supply utilities requested a restriction on intake of tap water based on the provisional index level for radioactive caesium (200 Bq Kg-1). There was increased communication and collaboration between all stakeholders (the Ministry of Health, Labour and Welfare, water supply utilities, health departments of local governments, media, local residents, etc.). Public announcements were also made, especially about tap water restrictions for infants through television, the use of publicity cars for broadcasting by the local government, etc. However, people were still concerned about the health impacts under the emergency situation and were not satisfied with the announcements. As a result, citizens made many telephone calls to the health departments of local governments, water supply utilities and related organizations. When the restriction on infants’ intake of tap water was announced in the Tokyo metropolitan area for two days (23 and 24 March 2011), bottled water sold-out in stores very quickly. In response, the Bureau of Waterworks of the Tokyo Metropolitan Government announced at a press conference at 21:00 on 23 March that they would provide bottled water to homes with infant(s) aged 1 year or younger. Three 550 mL bottles of water were provided to families of about 80 000 nfants who lived in the served area (a total of approximately 240 000 bottles). Precipitation about 10 days after the nuclear power plant accident led to a very large amount of radioactive material being deposited from the atmosphere onto the land. This was the major cause of contamination of water sources. Therefore, ceasing abstraction of surface water sources after the precipitation reduced the concentration of radionuclides in tap water. In some water purification plants, covering the open-air basins for water treatment processes, including flocculation, clarification and sand filtration, with plastic sheets was performed in order to reduce contamination of the water via dry and wet deposition directly onto the basins. (In Japan, almost all finished water reservoirs are covered to prevent chemical and microbial contamination.) These measures were performed partly because there was not enough evidence of the effectiveness of powdered activated carbon treatment and particle separation in removing radionuclides from water. While some subsequent research has confirmed that the former treatment method was effective for iodine removal (Kosaka et al., 2012) and the latter for caesium removal (Kosaka et al., 2012; Tampo et al., 2016), covering the water treatment basins is still considered a relatively effective and pragmatic approach to prevent radionuclide contamination; the cover prevents the direct dry/wet deposition to the water surface. This is particularly important for iodine, as the effective treatment for removing it, as described above, is carried out before the water is stored in the treatment basins and, unlike radioactive caesium, sand filtration will not remove iodine (Kosaka et al., 2012). The following are lessons learned/recommendations for managing radionuclides in drinking-water in emergency situations. • Immediate response to a nuclear accident is of paramount importance. There is a need to establish criteria for drinking- water in an emergency situation and these should be established as part of emergency planning and preparedness. • Although the measurements of gross alpha and gross beta activity used for routine monitoring of drinking-water can also be used in an emergency situation, in this case those screening methods were inefficient, mainly because 131I may not be measured with the gross beta method as a result of volatilization during pre-treatment. • Techniques for measuring radionuclides in drinking-water in the event of an emergency should be established as part of emergency planning. Using the compiled information in the GDWQ on measurement techniques for the first time is not practicable during the response to an emergency. • Effective dialogue and collaboration between all the relevant stakeholders is of paramount importance during an emergency to provide clear messages to the public about the health risks, the developing situation and the measures in place. Non-emergency situation (existing exposure situation) after April 2012 From April 2012, the situation has been regarded as an existing exposure situation in terms of drinking-water (except for the areas under the evacuation order, which are excluded from this case study). In April 2012 a target level for management 92 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER of radionuclides in tap water was successively established. This target level replaced the provisional index levels and was derived directly from the guidance levels of the GDWQ (see below). The target value is 10 Bq Kg-1 for the sum of 134Cs and 137Cs, which has replaced the previous provisional index level for an emergency. Radioactive caesium is the only substance that has a target level because the impact of 131I from the nuclear power plant accident had disappeared from the general environment owing to its relatively short half-life (~eight days). Longer-term issues include the following. • There have been risk communication issues regarding consuming tap water for people returning home after the lifting of evacuation orders. Some people are still concerned about radioactive caesium in tap water because some water purification plants draw water from the dam where the sediment is contaminated with radioactive caesium, although the purified water does not exceed the target level for radioactive caesium. • There are concerns about the long-term behaviour in the water environment, especially the transfer of the remaining radioactive caesium in forest and mountainous areas to groundwater. This is unlikely to happen based on observation and prediction so far (for example, Tampo et al., 2016). • Disposal of sludge resulting from water purification processes: the sludge immediately after the nuclear accident contained high levels of 134Cs and 137Cs. In Japan, the sludge containing more than 8000 Bq Kg-1 (the sum of 134Cs and 137Cs) cannot be disposed of in normal landfills; it needs to be stored as radioactive waste. • The WHO guidance levels for 134Cs and 137Cs were directly applied to establish the target levels in drinking-water for the non-emergency (existing exposure) situation in Japan. However, the meaning and concept of the guidance levels are easily misunderstood by the public, and even by regulators and experts in the drinking-water division. They generally regard the guidance values as maximum allowable limits. There is therefore a need to improve communication on interpretation of the guidance levels. References Kosaka K, Asami M, Kobashigawa N, Ohkubo K, Terada H, Kishida N et al. (2012). Removal of radioactive iodine and cesium in water purification processes after an explosion at a nuclear power plant due to the Great East Japan Earthquake. Water Research. 46(14):4397–4404. MHLW (2011a). The survey results of radioactive materials in tap water. The 10th subcommittee for environmental health and water supply, Health Sciences Council held on April 19, 2011 (http://www.mhlw.go.jp/english/topics/2011eq/dl/Document2.pdf, accessed 2 February 2018). MHLW (2011b). Handling of food contaminated by radioactivity (relating to the accident at the Fukushima Nuclear Power Plant) (Press release). Tokyo: Department of Food Safety, Ministry of Health, Labour and Welfare, March 17, 2011 (http:// www.mhlw.go.jp/english/topics/foodsafety/dl/food-110317.pdf, and http://www.mhlw.go.jp/english/topics/foodsafety/ dl/110318-1.pdf, accessed 2 February 2018). MHLW (2011c). Response to contamination of tap water following accidents at the Fukushima nuclear power plants 1 and 2, 2011 [in Japanese]. Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare, 19 March 2011 (http://www.mhlw.go.jp/stf/houdou/2r98520000014tr1-img/2r98520000015k18.pdf, accessed 7 March 2018). MHLW (2011d). Handling of the index levels on radioactive materials in tap water, etc. (Press release). Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare, April 4, 2011 (http://www.mhlw.go.jp/english/topics/2011eq/dl/april_8_01.pdf, accessed 31 January 2018). . 93MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Ch ap ter 4. C A S E S T U D IE S MHLW (2012). Measures against radioactive materials in tap water. Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare (http://www.mhlw.go.jp/english/topics/2011eq/dl/Document_121011.pdf, accessed 31 January 2018). Tampo R, Ohno K, Konuma S, Aruga T, Igarashi D, Saito T et al. (2016). A study on adsorptive removal of dissolved cesium using local clay and bentonite clay [in Japanese]. In: Proceedings. The 50th Annual Conference of Japan Society on Water Environment, Tokushima, Japan, 16–18 March. Tokyo: Japan Society on Water Environment; 2016:466. WHO (2012). Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami. Geneva: World Health Organization (http://www.who.int/ionizing_radiation/pub_meet/fukushima_dose_assessment/ en/, accessed 20 October 2017). WHO (2013). Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary dose estimation. Geneva: World Health Organization (http://www.who.int/ionizing_radiation/ pub_meet/fukushima_risk_assessment_2013/en/, accessed 20 October 2017). 94 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER REFERENCES REFERENCES Annanmaki M & Turtianen T (2000). Treatment technologies for removing natural radionuclides from drinking-water. Final report of the TENAWA project, STUK-A169. Helsinki: Radiation and Nuclear Safety Authority (http://www.iaea.org/inis/ collection/NCLCollectionStore/_Public/32/018/32018426.pdf, accessed 28 September 2017). BfS (2009). Strahlenexposition durch natürliche radionuklide im Trinkwasser in der Bundesrepublik Deutschland. [Radiation exposure by natural radionuclides in drinking-water in the Federal Republic of Germany.] Eds. Beyermann M, Bünger T, Gehrcke K. und Obrikat D. Bundesamt für Strahlenschutz (Hrsg.), BfS SW 06/09, Salzgitter: 129 S (in German) (http:// nbn-resolving.de/urn:nbn:de:0221-20100319945, accessed 19 October 2017). BMG (2016). Trinkwasserverordnung in der Fassung der Bekanntmachung vom 10. März 2016. BGBl, Teil I Nr. 12: S. 459–491 Federal Ministry of Health (BMG) German Drinking-Water Ordinance (in German) https://www.bundesgesundheitsministerium. de/topics/drinking-water-ordinance/?L=0, accessed 20 March 2018). BMU (1986). Gesetz zum vorsorgenden Schutz der Bevölkerung gegen Strahlenbelastung (Strahlenschutzvorsorgegesetz – StrVG) vom 19. Dezember 1986. BGBL Teil I: S. 2610 (geändert in BGBL Teil I: S. 1474 vom 31. August 2015) Radiation Protection Precautionay Act (in German). Published in the Federal Law Gazette (BGBI Bundesgesetzblat). BMU (1987). Auswirkungen des Reaktorunfalls in Tschernobyl auf die Bundesrepublik Deutschland. Gemeinsamer Bericht der Leitstellen für das Jahr 1986. Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit (Hrsg.), Bonn (in German). BMU (2001). Verordnung über die Umsetzung von Euratom-Richtlinien zum Strahlenschutz (Strahlenschutzverordnung – StrlSchV) vom 20. Juli 2001. BGBl., Teil I Nr. 38: S. 1714–1846 Radiation Protection Ordinance (in German) Published in the Federal Law Gazette (BGBI Bundesgesetzblat). BMU (2006). Allgemeine Verwaltungsvorschrift zum Integrierten Mess- und Informationssystem zur Überwachung der Radioaktivität in der Umwelt (IMIS) nach dem Strahlenschutzvorsorgegesetz (AVV-IMIS) vom 13. Dezember 2006. bundesanzeiger Nr. 244a: S. 4–80 (in German). Brown J, Hammond D & Wilkins BT (2008a). Handbook for assessing the impact of a radiological incident on levels of radioactivity in drinking-water and risks to water treatment plant operatives. Chilton: Health Protection Agency (https:// www.gov.uk/government/uploads/system/uploads/attachment_data/file/340109/HPA-RPD-040_for_website.pdf, accessed 19 October 2017). 96 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER Brown J, Hammond D & Wilkins BT (2008b). Handbook for assessing the impact of a radiological incident on levels of radioactivity in drinking-water and risks to water treatment plant operatives: supporting scientific report. Chilton: Health Protection Agency (http://www.dwi.gov.uk/research/completed-research/reports/DWI70-2-192_supporting.pdf, accessed 19 October 2017). Brown J, Watson S & Nisbet AF (2015). UK recovery handbooks for radiation incidents 2015. Drinking-water supplies handbook. Version 4. London: Public Health England (https://www.gov.uk/government/uploads/system/uploads/ attachment_data/file/433689/PHE-CRCE-018_Drinking_Water_Supplies_Handbook_2015.pdf, accessed 17 October 2017). Canada Nuclear Safety Commission (2016). Independent Environmental Monitoring Program (IEMP) [website]. Ottawa: Canada Nuclear Safety Commission (http://nuclearsafety.gc.ca/eng/resources/maps-of-nuclear-facilities/iemp/index- iemp.cfm, accessed 19 October 2017). Chen, J, Cooke, MW & Mercier, JF (2017). A review of natural radionuclides in Canadian drinking-water (1975–16). Radiat Prot Dosimetry. 176(1–2):1–11. CODEX (1981). CODEX standard for natural mineral waters. CXS 108-1981. Rome: Food and Agriculture Organization of the United Nations, Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission (www.fao.org/input/ download/standards/223/CXS_108e.pdf, accessed 19 October 2017). CODEX (2001). CODEX general standard for bottled/packaged drinking-waters (other than natural mineral waters), CXS 227- 2001. Rome: Food and Agriculture Organization of the United Nations, Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission (www.fao.org/input/download/standards/369/CXS_227e.pdf, accessed 19 October 2017). EC (1998). Council Directive 98/83/EC on the quality of water intended for human consumption. Brussels: European Commission (http://eur-lex.europa.eu/, accessed 19 January 2018). EC (2013). Council Directive 2013/51/EURATOM laying down requirements for the protection of the health of the general public with regard to radioactive substances in water intended for human consumption. Brussels: European Commission (http://eur-lex.europa.eu/, accessed 19 January 2018). El-Naser HK, Smith B, Kilani S, Abdeldin I, Howarth B, Saleh B (2016). Blending as the best compliance option for the management of radioactivity in drinking-water supplied from the deep sandstone aquifer in Southern Jordan. J Water Health. 14(3):528–48. Environment Agency et al. (2016). Radioactivity in food and the environment, 2015. Rotherham: Environment Agency, Food Standards Agency, Food Standards Scotland, Natural Resource Wales, Northern Ireland Environment Agency and the Scottish Environment Protection Agency (https://www.gov.uk/government/publications/radioactivity-in-food-and- the-environment-rife-reports-2004-to-2016, accessed 19 January 2018). EPA (2000). Radionuclides Rule under the Safe Drinking-Water Act, 66 Federal Register 76708, December 7, 2000. Washington (DC): United States Environmental Protection Agency (https://www.federalregister.gov/documents/2000/12/07/00-30421/ national-primary-drinking-water-regulations-radionuclides-final-rule). Health Canada (2017). Guidelines for Canadian drinking-water quality—summary table. Ottawa: Water and Air Quality Bureau, Healthy Environments and Consumer Safety Branch, Health Canada (https://www.canada.ca/content/dam/ hc-sc/migration/hc-sc/ewh-semt/alt_formats/pdf/pubs/water-eau/sum_guide-res_recom/sum_guide-res_recom- eng.pdf, accessed 19 October 2017). Hess CT, Vietti MA & Mage DT (1987). Radon from drinking-water – evaluation of water-borne transfer into house air. Environ Geochem Health. 9:68–73.IAEA (2011). Criteria for use in preparedness and response for a nuclear or radiological emergency. . 97MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER R E F E R E N C E S IAEA (2011). Criteria for use in preparedness and response for a nuclear or radiological emergency. IAEA Safety Standards Series No. GSG-2. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/ Pub1467_web.pdf, accessed 17 October 2017). IAEA (2014). Radiation protection and safety of radiation sources: International Basic Safety Standards. IAEA Safety Standards Series No. GSR Part 3. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/ Pub1578_web-57265295.pdf, accessed 17 October 2017). IAEA (2015). Preparedness and response for a nuclear or radiological emergency. IAEA Safety Standards Series No. GSR Part 7. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/P_1708_web. pdf, accessed 20 October 2017). IAEA (2016). Criteria for radionuclide activity concentrations for food and drinking-water. IAEA-TECDOC-1788. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/Publications/PDF/TE-1788_web.pdf, accessed 27 November 2017). IAEA (2018). A arrangements for the termination of a nuclear or radiological emergency (GSG-11). IAEA-Safety Standards Series No. GSG-11. Vienna: International Atomic Energy Agency (https://www-pub.iaea.org/MTCD/Publications/PDF/ PUB1796_web.pdf, accessed 15 May 2018) ICRP (2009). Application of the Commission’s recommendations to the protection of people in emergency exposure situations. Publication 109. Ann ICRP. 39(1)1–110. ISO (2006). ISO/NP 5667-1: Water quality – Sampling – Part 1: Guidance on the design of sampling programmes and sampling techniques. Geneva: International Organization for Standardization. ISO (2010). ISO/IEC 17025:2005. General requirements for the competence of testing and calibration laboratories. Geneva: International Organization for Standardization. Iwaoka K (2016). The current limits for radionuclides in food in Japan. Health Phys. 111(5):471–78. Jones F & Castle RG (1987). Radioactivity monitoring of the water cycle following the Chernobyl accident. Water Environ J. 1(2):205–217. Kleinschmidt R & Akber R (2008). Naturally occurring radionuclides in materials derived from urban water treatment plants in southeast Queensland, Australia. J Environ Radioact. 99:607–620. Kleinschmidt R, Black J & Akber R (2011). Mapping radioactivity in groundwater to identify elevated exposure in remote and rural communities. J Environ Radioact. 102:235–243. Kosaka K, Asami M, Kobashigawa N, Ohkubo, K, Terada H, Kishida N et al. (2012). Removal of radioactive iodine and cesium in water purification processes after an explosion at a nuclear power plant due to the Great East Japan Earthquake. Water Res. 46:4397–4404. Kosaka K, Watanabe S, Kobayashi Y, Sasaki M, Asami M, Oikawa T et al. (2014). Removal of radioactive iodine and cesium by powdered activated carbon and coagulation-sedimentation processes [in Japanese]. Journal of Japan Water Works Association. 83(1):7–22. MHLW (2011). Handling of the index levels on radioactive materials in tap water, etc. (Press release). Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare, April 4, 2011 (http://www.mhlw.go.jp/english/ topics/2011eq/dl/april_8_01.pdf, accessed 31 January 2018). 98 . MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER MHLW (2012a). Measures against radioactive materials in tap water. Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare (http://www.mhlw.go.jp/english/topics/2011eq/dl/Document_121011.pdf, accessed 31 January 2018). MHLW (2012b). Notice on the replacement of provisional index levels for restriction on tap water intake [in Japanese]. Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare (http://www.mhlw.go.jp/ stf/houdou/2r98520000018ndf-att/2r98520000024of2.pdf, accessed 31 January 2018). Nazaroff WW, Doyle SM, Nero AV, Sextro RG (1987). Potable water as a source of airborne Rn-222 in US dwellings: a review and assessment. Health Phys. 52(3):281–289. Ohno K, Ogata T, Kawamura S, Sato H, Kosaka K, Asami M et al. (2013). Behaviour of low level radioactive caesium ion during conventional water purification processes. Proceedings. The 8th International Water Association Micropol & Ecohazard, Zurich, Switzerland, June 2013:138–139. SSK (1988). Auswirkungen des Reaktorunfalls in Tschernobyl auf die Bundesrepublik Deutschland Veröffentlichungen der Strahlenschutzkommission – Band 7 [Effects of the reactor accident in Chernobyl on the Federal Republic of Germany. Publications of the Radiation Protection Commission]. Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit (Hrsg.). Stuttgart: Gustav Fischer Verlag (in German). Tagami K & Uchida S (2011). Can we remove iodine-131 from tap water in Japan by boiling? Experimental testing in response to the Fukushima Daiichi nuclear power plant accident. Technical Note. Chemosphere. 84(9):1282–1284. UNSCEAR (2000). Sources and effects of ionizing radiation. Volume I: Sources. New York (NY): United Nations Scientific Committee on the Effects of Atomic Radiation (http://www.unscear.org/unscear/en/publications/2000_1.html, accessed 20 October 2017). UNSCEAR (2008). Sources and effects of ionizing radiation. Volume I: Sources: Report to the General Assembly and Scientific Annexes A and B. New York (NY): United Nations Scientific Committee on the Effects of Atomic Radiation (http:// www.unscear.org/unscear/en/publications/2008_1.html, accessed 20 October 2017). UNSCEAR (2016). Sources, effects and risks of ionizing radiation. Annex D – Biological effects of selected internal emitters—Uranium. New York (NY): United Nations Scientific Committee on the Effects of Atomic Radiation (http://www.unscear.org/docs/publications/2016/UNSCEAR_2016_Annex-D.pdf, accessed 20 October 2017). USEPA (2005). A regulators’ guide to the management of radioactive residuals from drinking-water treatment technologies. Washington (DC): United States Environmental Protection Agency (https://www.epa.gov/sites/production/files/2015-05/ documents/816-r-05-004.pdf, accessed 20 October 2017). WHO (2009). WHO handbook on indoor radon. A public health perspective. Geneva: World Health Organization (http:// www.who.int/ionizing_radiation/env/9789241547673/en/, accessed 27 November 2017). WHO (2012). Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami. Geneva: World Health Organization (http://www.who.int/ionizing_radiation/pub_meet/fukushima_dose_assessment/ en/, accessed 20 October 2017). WHO (2013). Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary dose estimation. Geneva: World Health Organization (http://www.who.int/ionizing_radiation/ pub_meet/fukushima_risk_assessment_2013/en/, accessed 20 October 2017). . 99MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER R E F E R E N C E S WHO (2017a). Guidelines for drinking-water qualityfourth edition incorporating the first addendum. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/publications/drinking-water-quality-guidelines-4-including- 1st-addendum/en/, accessed 27 November 2017). WHO (2017b). Iodine thyroid blocking: guidelines for use in planning for and responding to radiological and nuclear emergencies. Geneva: World Health Organization; 2017 (http://www.who.int/ionizing_radiation/pub_meet/iodine- thyroid-blocking/en/, accessed 17 January 2018). 100 .MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER CALCULATION OF DOSES AND GUIDANCE LEVELS FOR SPECIFIC NON- EMERGENCY SITUATIONS Annex 1 A.1 Doses to children from the consumption of drinking-water If a guidance level is exceeded, it is important that there is further investigation; this may include a site-specific assessment for the population affected and can take into account their drinking-water consumption habits. In the case of there being a prolonged period over which a guidance level is exceeded, an assessment of doses to children and babies drinking bottled milk reconstituted with drinking-water may be appropriate. This is because children are more sensitive to exposure from some radionuclides, although they typically consume smaller quantities of drinking-water than adults. The calculation of doses for children can be made using age-specific values for consumption of drinking-water and ingestion dose coefficients. The equation is: D = A x C x I Where: D = annual dose (mSv y-1) A = radionuclide activity concentration in drinking-water (Bq L-1) C = consumption rate of drinking-water for relevant age group (L y-1); see Table A.1 I = ingestion dose coefficient for relevant age group (mSv Bq-1); see Table A.2 A.2 Drinking-water consumption rates Drinking-water consumption rates can vary considerably between countries and age groups, depending on the habits of the population and the climate (Howard & Bartram, 2003). Daily water intake can vary significantly in different parts of the world, seasonally and particularly where consumers are involved in manual labour in hot climates. Therefore, where local drinking-water consumption data exist, it is important this information is used to calculate the doses. In cases where local or national data are not available, information from neighbouring countries within a region is also likely to be more appropriate than worldwide averaged data. It is also important to investigate if tap water is used for making bottled milk for babies. If country- or region-specific data are not available, the doses to children from the consumption of drinking-water can be assessed using the default values given in Table A.1. Table A.1. Default consumption rates of drinking-water for children Age Litres day-1 Comments Reference Infant (< 6 months) 0.75 Bottle-fed babies, feed made with tap water. Based on a body weight of 5 kg WHO (2017) Young child 1.0 Based on a body weight of 10 kg, i.e. child aged about 1 year WHO (2017) All children 1.0–2.0 Consumption rates variable within this range and depend on habits, body weight and climate IPCS (1994); Howard & Bartram (2003) 102 .MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER A summary of country-specific average drinking-water consumption data is given in Quantitative microbial risk assessment: application for water safety management (WHO, 2016) based on a number of studies. A number of important aspects are identified that can influence the analysis and interpretation of consumption data, which should be taken into account when such surveys are conducted (WHO, 2016; Mons et al., 2007). A.3 Ingestion dose coefficients for children Ingestion dose coefficients for all age groups, including children and infants, are provided by the International Commission on Radiological Protection (ICRP, 2012). Values are given in Table A.2 for the common natural and human-made radionuclides listed in Chapter 9 (Table 9.2) of the GDWQ (WHO, 2017). Values for other radionuclides are given in ICRP (2012). It should be noted that the values given for infants are for babies on a milk diet, typically aged less than 6 months. If infants are consuming food, it is more appropriate to use the values for a 1-year-old child. As can be seen in Table A.2, the difference in the values for children aged 1 year and 10 years is no more than a factor of about two (except for iodine-131) and all children (other than bottle fed babies) could be considered as a single age group, with the range of doses considered using the consumption rate for drinking-water in Table A.1. If drinking-water contains iodine-131, it may be appropriate to carry out a more detailed assessment of doses as a function of age. Table A.2. Ingestion dose coefficients for different ages Radionuclide Dose coefficient (mSv/Bq-1)a,b Adults Infants (< than 6 months old)c Children (1‑y‑old) Children (10‑y‑old) Tritium 1.8 x 10-8 6.4 x 10-8 4.8 x 10-8 2.3 x 10-8 Carbon-14 5.8 x 10-7 1.4 x 10-6 1.6 x 10-6 8.0 x 10-7 Strontium-90 2.8 x 10-5 1.3 x 10-4 7.3 x 10-4 6.0 x 10-4 Iodine-131 2.2 x 10-5 4.8 x 10-4 1.8 x 10-4 5.2 x 10-5 Caesium-134 1.9 x 10-5 2.6 x 10-5 1.6 x 10-5 1.4 x 10-5 Caesium-137 1.3 x 10-5 1.1 x 10-5 1.2 x 10-5 1.0 x 10-5 Lead-210 6.9 x 10-4 2.4 x 10-3 3.6 x 10-3 1.9 x 10-3 Polonium-210 1.2 x 10-3 5.6 x 10-2 8.8 x 10-3 2.6 x 10-3 Radium-226 2.8 x 10-4 5.7 x 10-3 9.6 x 10-4 8.0 x 10-4 Radium-228 6.9 x 10-4 3.0 x 10-2 5.7 x 10-3 3.9 x 10-3 Uranium-234 4.9 x 10-5 1.7 x 10-4 1.3 x 10-4 7.4 x 10-5 Uranium-238 4.5 x 10-5 1.4 x 10-4 1.2 x 10-4 6.8 x 10-5 Thorium-228 7.2 x 10-5 3.7 x 10-3 3.7 x 10-4 1.4 x 10-4 Thorium-230 2.1 x 10-4 4.1 x 10-3 4.1 x 10-4 2.4 x 10-4 Thorium-232 2.3 x 10-4 1.6 x 10-3 4.5 x 10-4 2.9 x 10-4 Plutonium-239/240 2.5 x 10-4 5.2 x 10-3 4.2 x 10-4 2.7 x 10-4 Americium-241 2.0 x 10-4 4.7 x 10-3 3.7 x 10-4 2.2 x 10-4 a Taken from WHO (2017) b Taken from ICRP (2012) c Values to be used for bottle-fed infants where tap water is used for making bottled milk . 103MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER An ne x 1 C A LC U L A T IO N O F D O S E S A N D G U ID A N C E L E V E L S F O R S P E C IF IC N O N -E M E R G E N C Y S IT U A T IO N S A.4 Guidance levels for specific situations Normally, it will be appropriate to use the guidance levels in the GDWQ. The guidance levels are likely to be conservative because they assume that drinking-water is consumed at this activity concentration for the whole year at a rate of 2 litres per day. If required, guidance levels can be calculated by a country for specific situations, for example drinking- water consumption rates that are country- or site-specific or for potentially more vulnerable population groups, such as children. For these situations, appropriate annual consumption rates of drinking-water and dose coefficients for ingestion are required. The guidance levels in the GDWQ are calculated in the following way, as described in Section 9.4 of the GDWQ: GLi = IDC hing x q Where: GL = guidance level in drinking-water for radionuclide i (Bq L-1) IDC = individual dose criterion (0.1 mSv y-1) q = annual consumption of drinking-water, assumed to be 730 L y-1 (2 L d-1) hing = adult dose coefficient for ingestion (mSv Bq-1). The equation above can be used, substituting local or regional consumption rates or age-specific consumption rates (parameter q). Default drinking-water consumption rates for children are given in Table A1 and ingestion dose coefficients for different ages for the common natural and human-made radionuclides listed in Chapter 9 (Table 9.2) of the GDWQ are given in Table A2. References Howard G & Bartram J (2003). Domestic water quantity, service, level and health. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/publications/wsh0302/en/, accessed 19 October 2017). ICRP (2012). Compendium of dose coefficients based on ICRP Publication 60. Publication 119. Ann ICRP. 41(Suppl 1). IPCS (1994). Environmental Health Criteria 170. Assessing human health risk of chemicals: derivation of guideline values for health-based exposure limits. Geneva: International Programme on Chemical Safety (http://www.inchem.org/ documents/ehc/ehc/ehc170.htm, accessed 20 October 2017). Mons MN, van der Wielen JM, Blokker EJ, Sinclair MI, Hulshof KF, Dangendorf F et al. (2007). Estimation of the consumption of cold tap water for microbiological risk assessment: an overview of studies and statistical analysis of data. J Water Health. 5(Suppl 1):151–70. WHO (2016). Quantitative microbial risk assessment: application for water safety management. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/publications/qmra/en/, accessed 20 October 2017). WHO (2017). Guidelines for drinking-water quality: fourth edition incorporating the first addendum. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/publications/drinking-water-quality-guidelines-4-including- 1st-addendum/en/, accessed 27 November 2017). 104 .MANAGEMENT OF RADIOACTIVITY IN DRINKING-WATER
ISBN 978-92-4-151374-6
饮用水中放射性管理 Management of Radioactivity in Drinking-water 世界卫生组织 著 吉艳琴 钱宇欣 译 孙全富 校 II © 中国疾病预防控制中心辐射防护与核安全医学所 2022 本译文不由世界卫生组织（WHO）翻译，WHO 不对此译文的内容或准确性负责。原始英文 版《Management of radioactivity in drinking-water》，日内瓦：世界卫生组织；2018. CC BY-NC-SA 3.0 IGO 为应遵守的正本。 此翻译版可在 CC BY-NC-SA 3.0 许可协议下使用。 III 目录 目录 ................................................................................................................................................. III 图表目录......................................................................................................................................... VI 前言 ............................................................................................................................................... VII 致谢 .............................................................................................................................................. VIII 缩写 .................................................................................................................................................. X 术语 ................................................................................................................................................. XI 1 非应急情况 ............................................................................................................................... 1 1.1 背景 .................................................................................................................................... 1 1.1.1 在非应急情况下饮用水中的放射性核素是否能构成公众健康风险? ............... 1 1.1.2 非应急情况下饮用水中放射性核素的可能来源是什么? ................................... 1 1.1.3 天然放射性核素如何进入饮用水？ ...................................................................... 2 1.1.4 在非应急情况下何时应考虑饮用水中的放射性核素? ........................................ 2 1.2 饮用水水质准则的目的和范围 ......................................................................................... 3 1.2.1 饮用水水质准则的目的是什么？ .......................................................................... 3 1.2.2 WHO 对饮用水中的放射性核素提供了哪些指导？............................................ 4 1.2.3 GDWQ 可以在什么情况下使用？ ........................................................................ 4 1.2.4 GDWQ 中的放射性指标是否强制性？ ................................................................ 4 1.2.5 为什么在放射或核应急情况下，GDWQ 中提供的标准不适用？ .................... 4 1.2.6 是否有规定瓶装和包装饮用水中放射性核素的国际标准？ ............................. 4 1.2.7 饮用水中的天然放射性核素和人工放射性核素是否应采取不同的管理？ ...... 5 1.3 WHO 采用的饮用水中放射性核素致公众健康风险的评估方法 ................................... 5 1.3.1 GDWQ 用于评估饮用水中放射性核素致健康风险的指标是什么？ ................. 5 1.3.2 如何理解个人剂量标准 0.1mSv/a？ ...................................................................... 5 1.3.3 使用筛查水平的目的及如何使用？ ...................................................................... 6 1.3.4 使用放射性核素指导水平的目的及如何使用？ .................................................. 6 1.3.5 指导水平是否需要针对儿童调整？ ...................................................................... 7 1.3.6 如何理解参考水平（1 mSv/a）？其与饮用水的个人剂量标准（0.1 mSv/a）有 何关系？ ........................................................................................................................... 7 1.4 饮用水中放射性核素的测定 ............................................................................................ 8 1.4.1 在供水系统链的哪个阶段应开展饮用水中放射性核素的测量？ ...................... 8 1.4.2 饮用水中放射性核素的测量频次应如何？ .......................................................... 8 1.4.3 是否有总 α 和总 β 标准筛查方法检测不到的放射性核素？ ............................ 10 1.5 GDWQ 方法如何应用于饮用水中的放射性核素.......................................................... 11 1.5.1 如果一个或少数几个饮用水样品超过筛查水平，这是否意味着辐射剂量将大 于个人剂量标准 0.1 mSv/a？ ........................................................................................ 11 1.5.2 如果未超过筛查水平，是否需要采取任何措施? .............................................. 11 1.5.3 如果饮用水样品超出任一筛查水平，需要采取什么进一步措施？ ............... 11 1.5.4 当总 β 活度浓度超过筛查水平时，从中扣除钾-40 贡献的原因是什么？如何 执行？ ............................................................................................................................. 13 1.5.5 如何识别饮用水中哪些放射性核素导致超出筛查水平？ ............................... 14 1.5.6如果测量饮用水中具体放射性核素超过个人剂量标准 0.1 mSv/a将如何评价？ ......................................................................................................................................... 14 IV 1.5.7 如果饮用水中所测放射性核素的活度浓度未超过指导水平，这是否意味着无 需采取进一步措施？ ..................................................................................................... 15 1.5.8 如果超过了 0.1 mSv/a 的个人剂量标准，是否表示饮用水不适合饮用？ ..... 16 1.5.9 如果超过了指导水平或放射性核素的总和超过了 0.1 mSv/a 个人剂量标准， 下一步该怎么办? ........................................................................................................... 16 1.5.10 基于 GDWQ 和基本安全标准建立国家标准的考虑因素是什么？ ............... 19 1.5.11 降低饮用水中放射性核素活度浓度有什么可能的选项？ ............................. 21 1.6 饮用水中的氡 .................................................................................................................. 23 1.6.1 氡如何进入饮用水？ ........................................................................................... 23 1.6.2 是否需要建立饮用水中氡的国家标准？ ........................................................... 23 1.6.3 应在供水链中哪一点开展饮用水中氡的测量？ ................................................ 23 1.6.4 哪些方法可以应用于饮用水供应中氡的采样和测量？ ................................... 23 1.6.5 水源中氡浓度高时如何管理饮用水中的氡？ .................................................... 24 2 应急情况 ................................................................................................................................. 25 2.1 管理饮用水水质的应急情况和标准的背景 ................................................................... 25 2.1.1 什么是放射应急情况？ ........................................................................................ 25 2.1.2 核或放射事故应急后，饮用水中的放射性核素是否可能存在长期的公众健康 风险？ ............................................................................................................................. 25 2.1.3 应急情况何时结束且这对饮用水水质有何考虑？ ............................................ 25 2.1.4 是否有适用于应急情况下饮用水水质的国际标准和准则？ ............................ 25 2.2 发生核或放射应急情况时饮用水的健康风险 ............................................................... 26 2.2.1 在核或放射应急情况下饮用水中可能涉及哪些放射性核素？ ........................ 26 2.2.2 在核或放射应急情况下，建立饮水标准时是否儿童需要更严格的防护？ .... 27 2.2.3 在核或放射应急情况下，与其他照射途径相比饮用水中放射性核素所致的健 康风险如何？ ................................................................................................................. 28 2.3 在应急情况下测量饮用水中的放射性核素 ................................................................... 28 2.3.1 在核或放射应急情况下哪些筛查方法用于测量饮用水中的放射性核素？ .... 28 2.3.2 核或放射应急期间可能会影响哪种类型的水源？ ............................................ 29 2.3.3 在核或放射应急期间重点监测哪些水源？ ........................................................ 29 2.4 应急情况下超出饮用水标准的管理 ............................................................................... 30 2.4.1 在核或放射应急时如何使用饮用水的操作干预水平？ .................................... 30 2.4.2 如果超过应急情况下的饮用水标准，需要采取什么行动？对于小型供水，包 括社区供水，是否要采取特殊行动？ ......................................................................... 31 3 支持信息 ................................................................................................................................. 34 3.1 煮沸的水会减少饮用水中放射性核素的照射吗？ ....................................................... 34 3.2 从饮用水中去除放射性核素的水处理方法有何效果？ ............................................... 34 3.3 如果通过处理去除了饮用水中的放射性核素，水处理过程的废物是否需要作为放射 性废物处理，将终止于何处？ ............................................................................................. 36 3.4 处理含放射性核素水的工作人员有何健康风险？ ....................................................... 37 3.5 采用哪些方法测量供水中的放射性核素？ ................................................................... 38 4 案例分析 ................................................................................................................................. 42 4.1 巴西 .................................................................................................................................. 42 4.2 加拿大 ............................................................................................................................... 44 4.3 约旦 ................................................................................................................................... 46 V 4.4 瑞典 ................................................................................................................................... 48 4.5 日本 ................................................................................................................................... 51 参考文献......................................................................................................................................... 54 附录 A ............................................................................................................................................. 59 非应急情况特定剂量和指导水平的计算 ..................................................................................... 59 A.1 儿童饮用水的剂量 .......................................................................................................... 59 A.2 饮水量 .............................................................................................................................. 59 A.3 儿童的摄入剂量系数 ...................................................................................................... 60 A.4 特定情况下的指导水平 .................................................................................................. 60 VI 图表目录 图 1.1 GDWQ 各章节在确保饮用水安全方面的相互关系 .................................................. 3 图 1.2 饮用水中放射性核素测量流程图 ............................................................................ 13 图 2.1 在应急情况下应用 OIL 的分阶段方法 .................................................................... 31 图 4.1 运输系统的简化方案 ................................................................................................. 47 表 1.1 饮用水中常见放射性核素的 WHO 指导水平汇总 .................................................. 14 表 1.2 常见放射性核素的指导水平 ..................................................................................... 17 表 1.3 根据个人剂量水平建议采取措施的汇总 ................................................................. 19 表 1.4 制定国家标准或参考水平的框架 ............................................................................. 19 表 2.1 核或放射应急情况下饮用水可能涉及的放射性核素 ............................................. 27 表 3.1 地表水和地下水特征 ................................................................................................. 34 表 3.2 水处理性能 ................................................................................................................. 35 表 3.3 测量饮用水中放射性核素的不同方法主要特性 ..................................................... 39 表 4.1 约旦监测饮用水中放射性核素后遵循的干预措施 ................................................. 48 表 A 1 儿童的默认饮水率 ..................................................................................................... 59 表 A 2 不同年龄的摄入剂量系数 .......................................................................................... 60 VII 前言 本指南的由来 世界卫生组织饮用水水质准则（WHO GDWQ）（WHO, 2017a）为确保饮用 水安全、制定国家的条列、标准以及风险管理战略提供了基本原则。 尽管准则包括非应急情况下饮用水中放射性相关的指导（见 2011 年版本既 2017 年出版的第 9 章），成员国仍希望提供可操作性的建议以支持相关使用方 在执行或解释 GDWQ 时，该如何采取合适的行动，因此，参考在执行 GDWQ 第 9 章方面取得的经验和知识，制定饮用水中放射性管理这一指南，同时也将促 进和支持实现各国相关饮用水标准的制定。 此外，按成员国提出的要求，亦编写包括了关于核或放射应急情况下的相关 指导建议，旨在提高对国际标准或准则的理解和促进饮用水供应的管理。 目标读者 本指南中的问与答(Q&A) 目的用于国家或地区组织制定或实施饮用水中 放射性相关标准及风险管理，同时为解决饮用水中相关放射性问题的机构提供 支持。因此，本指南将适用于供水系统人员、饮用水监管人员、辐射防护专业 人员以及应急管理人员。 本指南不是为公众编写的宣传材料，但它有助于相关材料的编制。 本指南说明 本指南是关于饮用水水质放射性方面以问与答形式编写。每个问题和答案相 对独立、与其他问答相互连接补充，不需要从头至尾阅读。 本指南分为四个部分： 第 1 章 关于非应急情况，提供 GDWQ 的基本信息，以及此情况下饮用水 中放射性核素对公众健康的风险评估和管理方面WHO所采纳方法的说明。 关于氡的信息，包括风险评估和管理单独为一章节，氡的评估和管理方法 与其它放射性核素对比不同。 第 2 章 关于应急情况，提供了与在非应急情况下类似的信息，但属于应 急范畴。 第 3 章 提供对非应急情况和应急情况都很常见的支持信息，包括关于治 理和分析方法的信息。 第 4 章 包括一些国家如何管理饮用水中放射性的案例分析。 本指南还包括一个附件，支持计算具体的非应急情况的剂量和指导水平。 对于非应急情况，GDWQ 中的相关信息概括在了该指南中以便实际应用， 读者可结合 GDWQ（WHO, 2017a）第 9 章使用本指南。 VIII 致谢 本指南是世界卫生组织的水、环境卫生和健康组以及辐射项目组共同合作完 成。WHO 向为本书贡献了他们的时间、专业知识和经验的所有人表示衷心感谢。 编写人员 Jennifer De France，Maria Perez，Bruce Gordon 和 Emilie van Deventer 在 WHO 组成了秘书处，协调本指南的编写工作。WHO 特别感谢本指 南的主要撰写人独立顾问 Joanne Brown（原就职于英国公共卫生部），她在起草 和审阅本指南的过程中向编写组提供了宝贵的建议及帮助。感谢 Koichi Ohno 对 筹备第一次工作组会议的技术支持。 对以下专家表示感谢，感谢他们在两次工作组会议中以及起草和审阅中共同 为编写本指南作出的贡献： Hamed Bakir，WHO 东地中海区域办事处，约旦 Jing Chen，加拿大卫生部，加拿大 John Fawell，克兰菲尔德大学，英国 Susan Kilani，水利部，约旦 Nthabiseng Mohlala，国家核监管机构，南非 Teofilo Monteiro, WHO 泛美卫生组织，秘鲁 Koichi Ohno, 原就职于国家公共卫生研究所，日本 Kirlna Skeppström, 原就职于辐射安全管理局，瑞典 Barry Smith, 英国独立顾问，英国 Katherine Snead，环境保护部，美国 Lene Veiga, 原就职于辐射防护和剂量学研究所，巴西 还感谢来自巴西、加拿大、日本、约旦和瑞典的工作组参加人员编写了第 4 章所列的案例分析。 饮用水和辐射防护两方面的许多专家通过同行审阅并提供补充相关资料亦 作出了贡献： Mari Asami，国家公共卫生研究所，日本 Francesco Bochicchio，国家辐射防护和计算物理中心，意大利 Jane Bradley, 英国公共卫生部，英国 Tony Colgan, 国际原子能机构，奥地利 Joseph Cotruvo, 美国独立顾问，美国 David Cunliffe,南澳大利亚卫生部，澳大利亚 Michael Davidson，英国公共卫生部 ，英国 Isabelle Dublineau，放射防护和核安全研究所，法国 Sybille Estier，公共卫生联邦办公室，瑞士 Mariza Ramalho Franklin，辐射防护和剂量学研究所，巴西 Klaus Gehrcke，辐射防护联邦办公室，德国 Marc Gleizes，放射防护和核安全研究所，法国 Hans-Jürgen Grummt，德国环境署，德国 Joanne Hunt，饮水检查局，英国 IX Darryl Jackson，独立顾问，澳大利亚 Christian Lucks, 辐射防护联邦办公室，德国 Kelly Jones，英国公共卫生部 ，英国 Neil McColl，英国公共卫生部 ，英国 Helgard Muller，独立顾问，南非 Svetlana Nestoroska-Madjunarova, 国际原子能机构，奥地利 Jan Pietersen，Midvaal 水公司，南非 Alain Rannou，放射防护和核安全研究所，法国 Donald Reid，环境部，加拿大 David Sheehan，Coliban Water，澳大利亚 Luís Simas，水和废物服务管理局，葡萄牙 Bo Thunholm，地质调查局，瑞典 Rick Tinker, 澳大利亚辐射防护和核安全局，澳大利亚。 Christiane Wittwer，辐射防护联邦办公室，德国 Muhd Noor M. Yunus，原子能许可董事委员会，马来西亚 由 WHO、IAEA 及其它合作机构联合组织的三个区域性研讨会的参会者也 提供了反馈意见。 WHO 感谢英国国际发展部、日本卫生部厚生劳动省和约旦水利部提供的资 助。 X 缩写 ALARA 可合理达到尽可能低原则 （辐射防护原则） Bq 贝可勒尔（放射性活度单位） BSS 基本安全标准 EC 欧洲委员会 FAO 联合国粮食及农业组织 GDWQ 饮用水水质准则 IAEA 国际原子能组织 ICP-MS 电感耦合等离子体质谱 ICRP 国际放射防护委员会 IDC 个人剂量标准 ILO 国际劳工组织 LOD 检测限 mSv 毫希沃特 NaI 碘化钠 NEA 核能机构 OECD 经济合作与发展组织 OIL 预置操作干预水平 PAHO 泛美卫生组织 Sv 希沃特 UNEP 联合国环境规划署 UNSCEAR 联合国原子辐射效应科学委员会 WHO 世界卫生组织 XI 术语 活度（Activity）：见“放射性”。 活度浓度（Activity concentration）：以单位体积活度表示的放射性的量，如 Bq/L 或 Bq/kg。另见“放射性”和“贝可勒尔”。 粒子（Alpha particles）：某些放射性同位素在衰变过程中发射出的由两个中子 和两个质子结合的一种粒子；一种与氦原子的原子核难以分辨的带正电荷的粒子， 粒子几乎无法穿透人体皮肤的外表皮，因此发射出粒子的放射性核素只有进 入人体内比如吸入或摄入时才有危险。 原子（Atoms）：任一化学元素能保持其化学性质的最小微粒。它们由一个致密 的原子核（含带正电荷的质子和电中性的中子）和周围环绕着带负电荷的电子云 组成。 贝可勒尔（Becquerel）：放射性原子的自发衰变称为“放射性”，或称为“活度”。 放射性的量以每秒自发衰变的次数来衡量。贝可勒尔（Bq）是国际单位制的放 射性活度单位，为每秒一次核衰变。 β 粒子（Beta particles）：从原子核发射的带负电荷的粒子，其质量等于电子的 质量。β粒子可穿透一厘米左右的组织，因此发射β粒子的放射性核素对浅表组 织有害，但对内脏器官没有危害，除非它们被吸入或食入体内。 保守算法（Conservative）：一种人为的选择更可能高估而不是低估风险的方法 （例如假设）。 单位消耗量（Consumption rate）：在给定的时间间隔内，以适当的计量单位表 示的一种物品的平均消耗量，例如每天的饮水量（升/天）。 剂量（Dose）：在本指南中，指辐射在某一目标物上沉积能量的量度。另见“有 效剂量”。 剂量系数（Dose coefficients）：用于将放射性核素摄入量换算成组织（或器官或 全身）剂量的系数。这些系数（也称为“剂量转换因子”）可能取决于放射性核素、 摄入途径（如吸入、食入）、化学组成以及人员年龄。通常表示为每单位摄入量 的剂量，例如：希沃特/贝克勒尔。 剂量转换因子（Dose conversion factor）：见“剂量系数”。 有效剂量（Effective dose）：每个器官的剂量乘以该组织的辐射加权因子（考虑 到组织和器官的辐射敏感性）的和。 相关术语 “剂量”。 应急情况（Emergency situation）：在本指南中，指需要立即采取行动以避免或 减少辐射照射对人类和/或环境产生不良后果的情况。事故、恶意行为或任何其 他意外事件都可能导致应急照射，应急情况下公众和职业人员（比如在应急响应 中执行任务的人员）可能受到照射。 XII 照射（Exposure）：在本指南中，指受到来自身体外部（即外照射）或身体内部 （即内照射）辐照的状态或行为。 照射途径（Exposure pathway:）：在本指南中，辐射或放射性核素能够到达人体 并产生照射的途径。 外照射（External exposure）：见“照射”。 γ射线（Gamma rays）：从原子核内发射的没有质量、不带电荷（即光子）的短 波长的电磁辐射；其类似于 X 射线，但衰变原子能发射出特定的特征能量。射 线可以穿过躯体，因此发射射线的放射性核素无论在体外还是在体内都可能有 害。 总 α（活度浓度）（Gross alpha (activity concentration) ）：所有发射 α 粒子的总 放射性，用单位体积的放射性活度表示（如 Bq/L）。筛查测量的总 α 不提供确 定的发射 α 射线的放射性核素及其活度浓度。 总 β（活度浓度）（Gross beta (activity concentration) ）：除氚和其它发射弱 β 射线的所有发射 β 粒子的总放射性，以单位体积的放射性活度表示（如 Bq/L）。 筛查测量的总 β 不提供确定的发射 β 射线的放射性核素及其活度浓度。 地下水（Groundwater）：地面以下岩石或底土中含有的水，可在地下含水层中 积聚。 指导水平（Guidance level）：本指南中所规定的放射性核素的活度浓度，即这些 核素存在于饮用水中，按每天 2 升的饮水量一年所致个人剂量将为 0.1 毫希沃 特 (mSv)。 半衰期（Half-life）：放射性核素的量有半数发生衰变时所需要的时间。 危害（Hazard:）：可能对人体健康造成损害的生物、化学或物理因素。 健康效应（Health effect:）：通过诊断或流行病学方法确定的个人或人群健康状 况的变化。 个人剂量标准（Individual dose criterion:）：本指南指饮用水中放射性核素的长 期照射所致健康风险的标准。一年饮水所致的个人剂量标准（IDC）为 0.1 毫希 沃特（mSv）。在实践中，这一标准被转化为两个可操作的量值：筛查水平和指 导水平。另见“筛查水平”和“指导水平”。 食入（Ingestion）：本指南中指放射性核素通过胃肠道进入人体。 摄入（Intake）：放射性核素在给定时间段或由特定事件而进入人体（通过食入、 吸入或经由皮肤）的过程。 内照射（Internal exposure）：本指南中，指放射性物质通过食入、吸入或经由皮 肤进入人体内引起的辐射照射。放射性物质在体内的整个过程中都会产生照射， 直到放射性物质不再具有放射性（自发衰变）或通过尿液、粪便等排出体外。另 见“照射”。 电离辐射（Ionizing radiation:）：辐射指有足够高的能量，能使物质/组织的原子 失去电子而电离形成离子对，例如 α 粒子、β 粒子和 γ 射线。 XIII 矿泉水（Mineral water）：从地下深处自然涌出或地下水经钻井而得。为了确定 天然矿泉水，需要满足国际食品法典委员会标准 108-1981 定义的若干准则。 天然本底辐射（Natural background radiation）：人群受到的天然照射的量，例如 土壤中的天然放射性核素产生的地球辐射、源于外层空间的宇宙辐射以及人体中 存在的天然放射性核素。 非应急情况（Non-emergency situations）：本指南中计划性活动所致的照射（例 如，核医学设施或核电站正常运行时的放射性排放），或决定对现存照射需要采 取控制措施时（例如天然本底辐射照射、在已宣布应急结束后先前的核或放射事 故中残留放射性物质的照射）的情况。 核应急（Nuclear emergency:）：涉及原子裂变或聚变的辐射照射造成或预期将造 成危害情况时的应急。裂变和聚变与核电厂发电、科学研究以及核武器试验/使 用有关。另见“应急情况”。 参数值（Parametric value）：《欧盟饮用水水质指令》关于供人类饮用的水中放 射性物质的值，超过该值成员国应评估此类放射性物质的存在是否对人类健康构 成风险、是否需要采取行动，并在必要时应采取补救措施，将水质改善至符合从 辐射防护角度保护人类健康的要求。 辐射（Radiation）：穿透物质的能量。本指南中该术语指电离辐射。另见“电离 辐射”。 放射性衰变（Radioactive decay）：不稳定原子的原子核自发地发出α粒子、β 粒子、γ 射线以及其它粒子形式的辐射。另见“原子”、“辐射”、“α 粒子”、 “β 粒子”和“γ 射线”。 放射性物质（Radioactive material）：含有不稳定原子的物质，在其衰变时会发 出辐射。另见“放射性衰变”。 放射性（亦称“活度”）（Radioactivity (also called "activity")）：不稳定原子的原 子核自发地以光子（例如 γ 射线）或亚原子粒子（例如α或β粒子）的形式释放 能量的性质。放射性的量定义为单位时间的平均衰变次数。另见“贝可勒尔”。 放射应急（Radiological emergency:）：由于医疗、工业或研究中使用的放射性装 置或放射性物质的辐射照射造成或预期将造成危害情况时的应急。另见“应急情 况”。 放射性核素（Radionuclide）：放射性的核素，其原子特征是不稳定的原子核， 能自发转变以辐射的形式释放能量。 参考水平（Reference level）：在辐射防护体系中指一种辐射剂量水平，高于该 水平不适合允许计划照射的发生，低于该水平将继续执行防护的最优化和安全。 补救措施（Remedial action）：见“补救”。 补救（Remedial）：本指南中，为减少辐射照射而采取的所有措施，通过对污染 物本身（源）或对所致人类照射的途径所采取的措施。 XIV 风险（Risk）：发生使人群遭受危害发生事件的可能性及其后果的严重性。在本 指南中，该术语指饮用水所致辐射照射的相关健康风险。 筛查水平（Screening level）：在本指南中，指饮用水中的放射性水平（用总 α 和总 β 放射性活度浓度表示），低于该水平则无需采取进一步措施。 水安全计划（Water safety plan:）：一种全面确保饮用水安全的风险评估和风险 管理方法，包括从集水区到消费者所有供水的步骤。 1 1 非应急情况 1.1 背景 1.1.1 在非应急情况下饮用水中的放射性核素是否能构成公众健康风险? 不能。与微生物和化学物质相比，饮用水中存在放射性核素的健康风险通常 非常低。饮用水中放射性核素对健康的任何影响都不是急性的或即时的。除特殊 情况外，饮用水中摄入放射性核素引起的辐射剂量要比从其它辐射源所致的辐射 剂量低得多（见信息栏 1.1）。 此外，在评估饮用水中放射性核素的健康风险时，无需考虑钾-40（40K）的 含量，因为钾是调节人体许多功能的关键元素，而人体的钾含量（包括 40K）通 过一系列生理过程保持恒定。 信息栏 1.1：天然辐射源的辐射剂量 饮食中天然来源的放射性核素通常所致公众的年辐射剂量约为 0.3 mSv；其中约 0.01 mSv（约 5％）来自饮用水。0.3 mSv 的剂量通常是各种天然辐射来源（宇宙射线、土壤、 氡、饮食）所致人均年辐射剂量约 2.4 mSv 的 10％（UNSCEAR, 2008）。 1.1.2 非应急情况下饮用水中放射性核素的可能来源是什么? 饮用水中的放射性核素来源于天然或人工（即人为活动）。自然界中包括岩 石和土壤中存在许多天然放射性核素，因此在饮用水中通常检测到的放射性核素 主要来源于地下水（IAEA, 2016）。饮用水所致人群辐射照射特别显著的核素为 来自于钍和铀衰变系列的天然放射性核素，比如镭-226、镭-228、钋-210、铅-210 以及氡。这些放射性核素可能因为地下的自然过程或涉及天然放射性物质的人类 活动而升高，例如铀矿开采和其他行业开采（煤炭，石油和天然气）、化肥（磷 酸盐）以及建筑业。信息栏 1.2 和 1.3 提供了全球饮用水中天然放射性核素活度 浓度的示例，以及德国天然本底贡献的辐射照射示例。 氡在本指南第 1.6 节中单独列出。 人工放射性核素可能存在于饮用水中，其来源有几种，比如核设施的事故或 常规排放，医学或工业中生产和应用的放射性核素排放，军事活动排放以及核武 器沉降灰的全球扩散。饮用水中可能发现的人工放射性核素为铯-134、铯-137、 锶-90、碘-131、氚和碳-14，这些放射性核素的含量通常极低，使用标准分析方 法通常无法检测到，也就是说它们低于检测限（见信息栏 1.4）。 信息栏 1.2：饮用水中天然放射性核素在全球的活度浓度 综述了全球饮用水中天然放射性核素水平的数据（UNSCEAR, 2000; 2008; 2016）。由 于地质作用天然放射性核素的活度浓度在一个国家/地区就可能变化很大，例如，全球公共 供水的水源中铀的平均水平显示巨大的变化，尤其是地下水，其活度浓度范围为 0.00001 Bq/L～200 Bq/L，不过，饮用水样品中很少（通常<3％）超过国家或国际标准中铀的指导值 （UNSCEAR, 2016）。饮用水中天然放射性核素在世界范围内的平均值是根据 UNSCEAR （UNSCEAR, 2000）广泛收集并最具代表性的数据所导出，表明饮用水中天然存在的放射 性核素其活度浓度通常极低。 2 饮用水中代表性的活度浓度，Bq/L 210 Pb 210 Po 226 Ra 228 Ra 228 Th 230 Th 232 Th 235 U 238 U 0.01 0.005 0.0005 0.0005 0.00005 0.0001 0.00005 0.00004 0.001 关键核素：铅-210 (210Pb)， 钋-210 (210Po)， 镭-226 (226Ra)， 镭-228 (228Ra)， 钍-228 (228Th)， 钍-230 (230Th)， 钍-232 (232Th)， 铀-235 (235U) 和铀-238 (238U)。 信息栏 1.3：德国饮用水中天然放射性核素对天然本底的年辐射照射贡献 作为德国系统研究的一部分，为获取德国饮用水中天然放射性核素对公众辐照的代表性 数据（BfS，2009），2003 年至 2008 年期间对来自公共供水的 582 个样本进行了分析，覆 盖了城市地区以及已知天然放射性核素活度浓度较高的地区（主要富含花岗岩/片麻岩的区 域，例如，厄尔士山脉和巴伐利亚地区），结果表明，德国饮用水中的天然放射性核素对天 然本底辐射照射的年平均值（2.1 mSv）贡献很小。根据德国《辐射防护条例》（BMU，2001） 假设成人每年摄入的饮水量为 350 升、婴儿摄入 55 升，调查数据表明成人由饮水摄入的年 个人剂量约 0.009 mSv，婴儿约 0.05 mSv。但是铀-238、铀-234、镭-226、镭-228、氡-222， 铅-210 和钋-210 的活度浓度变化范围相当大。 信息栏 1.4：饮用水中的人工放射性核素 各国的经验表明，作为许可的核设施周围饮用水水源监测计划的一部分，开展单一的人 工放射性核素检测，例如铯-137 和锶-90，通常都低于探测下限（例如 Environment Agency et al., 2016; Canada Nuclear Safety Commission, 2016; BMU, 1986; BMU, 2006）。 1.1.3 天然放射性核素如何进入饮用水？ 地壳中的所有物质都包含天然放射性核素，主要来自于铀和钍的衰变系列以 及钾-40。这些放射性核素通常以低浓度散布在整个岩石和土壤中，可能会渗入 地下水中（见信息 1.5）。因此与地表水和降雨相比，它们更常见于源自地下水 和泉水的饮用水中。 信息栏 1.5：饮用水中天然放射性核素的特性 铀、钍以及铀和钍衰变系列中各个放射性核素的水-化学行为复杂，并且很大程度上取 决于其它水质参数，比如碱度、pH、氧化还原和化学组成。比如，钍被认为在绝大多数天 然水体中相对稳定且不易溶解，尤其在 pH 值接近中性且具有高碳酸盐碱度的水中，而铀在 水中具有很高的流动性。 1.1.4 在非应急情况下何时应考虑饮用水中的放射性核素? 当预期有值得注意的放射性核素源进入饮用水供水系统，应考虑饮用水中的 放射性核素，这要预先评估岩石和土壤中天然放射性核素水平较高的区域。 涉及天然放射性物质的活动，例如铀矿开采和其它采矿业，以及工业和医学 中使用的人工放射性性核素也可能导致饮用水中含放射性核素（见 1.1.2）。 在某些情况下，例如某些地区深层的地下水源，其天然放射性核素所致的健 康风险可能比化学污染物大。 3 1.2 饮用水水质准则的目的和范围 1.2.1 饮用水水质准则的目的是什么？ 饮用水水质准则（GDWQ）的主要目的是保护公众健康。GDWQ 详细介绍 了世界卫生组织（WHO）关于饮用水安全管理中有害物（包括放射性）可能所 致健康风险的建议。同时应考虑这些有害物的其它来源，比如来自空气和食物的 风险管理。 GDWQ 提供了一种全面的方法来评估和管理饮用水安全风险。这种整体方 法即图 1.1 中所示的饮用水安全框架，包括制定基于健康目标（国家饮用水标准 中的指标和相关的“限值”），供水企业对风险的评估和管理（水安全计划）以 及独立监督以确保有效实施水安全计划并实现健康目标。通过确保解决最重大的 风险和最有效地利用有限的资源，用于饮用水供水的风险评估和风险管理的水安 全计划方法提高了人们对饮用水安全的信心。 GDWQ 第 9 章提供了有关饮用水水质放射性的具体支持信息，如图 1.1 所 示。 放射性的健康风险评估和管理需要结合供水带来的其它潜在健康风险，即微 生物和化学风险，考虑其它供水和可利用资源的实际情况。 GDWQ 主要面向水和卫生监管机构、政策制定者及相关顾问，以协助制定 国家标准。 图 1.1 GDWQ 确保饮用水安全各章节的相互关系 简介 （第 1 章） 实施准则的概念框架 （第 2 章） 安全饮用水框架 水安全计划（第 4 章） 系统评估 监测 管理与沟通 监督（第 5 章） 气候变化、应急、雨水蓄集、海水 淡化系统、旅客、飞机和轮船等 支持信息 微生物 （第 7 和 11 章） 化学 （第 8 和 12 章） 可接受性 （第 10 章） 放射性 （第 9 章） 4 1.2.2 WHO 对饮用水中的放射性核素提供了哪些指导？ GDWQ 提供饮用水水质准则，包括放射性方面（见 1.2.1）。 GDWQ 的第 9 章提供了管理和评估饮用水中放射性核素健康风险的具体信 息。 提供了标准（筛查水平和指导水平，见 1.3.1），该标准用于评估饮用水 水质中关于放射性核素的含量。 给出了一种解释健康标准的方法，以支持评估和管理饮用水中放射性核素 引起的健康风险，其中包括： ― 识别可能存在的具体放射性核素； ― 饮用水中放射性核素活度浓度的测量； ― 评估可能所致潜在的辐射剂量。 提供了有关可采取的减少饮用水中放射性核素活度浓度的补救措施的指 南。 提供了关于供水系统中氡引起的健康风险的指南。 1.2.3 GDWQ 可以在什么情况下使用？ GDWQ 中的放射性核素指南主要针对非应急情况，在这种情况下，可能因 为长期摄入含有放射性核素的饮用水，而导致个人长期的辐射照射，照射可能会 持续多年甚至一生。 GDWQ 中放射性核素的标准不适用于核与放射应急。对于应急情况，在其 它发布的国际标准，即国际原子能机构（IAEA）安全标准丛书（IAEA, 2011; 2015） 中包括了与饮用水有关的应急响措施，WHO 是此该丛书的参编机构（见 2.1.4）。 不过，GDWQ 中有关应急时饮用水水质总体规划和管理的信息，可能对核 或放射应急情况有用（参见 GDWQ 中的 4.4.3 和 6.7）。GDWQ 中有关分析方法、 补救措施以及水的有效处理等其它信息亦对发生核与放射应急情况时可能有用。 1.2.4 GDWQ 中的放射性指标是否强制性？ 不是。GDWQ旨在指导各国制定法规和标准的国际准则。各国在采纳 GDWQ 时应考虑其具体情况，包括保持不变使用其标准（即是否采用个人剂量标准 IDC、 筛查水平以及指导水平），1.5.10 涵盖了制定国家标准的注意事项。 1.2.5 为什么在放射或核应急情况下，GDWQ 中提供的标准不适用？ GDWQ 中放射性方面的标准（即个人剂量标准 IDC、筛查水平以及指导水 平）不适用于应急情况，因为它针对长期摄入（多年甚至一生）的饮用水而建立。 应急情况中，饮用水中放射性核素的活度浓度可能比非应急情况下高，其照射通 常仅在短期内发生，因此，在应急情况下使用的剂量标准显然高于 GDWQ 中的 IDC 和非应急情况下饮用水国际基本安全标准（BSS）的参考水平。第 2 章将描 述适用于应急情况下饮用水水质的国际标准，如 2.1.4。 一旦监管当局宣布应急终止，饮用水中残留的任何放射性核素从长远来看应 被视为非应急情况，并采用 GDWQ 标准。 1.2.6 是否有规定瓶装和包装饮用水中放射性核素的国际标准？ 食品法典委员会已颁布了瓶装/包装饮用水（天然矿泉水除外）的通用标准， 即 CODEX STAN 227-2001（CODEX, 2001），该标准规定水应符合 GDWQ 中 5 有关微生物、化学和放射物质的健康要求。食品法典委员会还有天然矿泉水的标 准 CODEX STAN 108-1981（CODEX, 1981），但是该标准中没有包括任何放射 性核素的准则。 对于应急情况，IAEA《安全标准丛书》中关于核和放射应急的准备与响应 的国际指南，包括《通用安全要求》第 7 部分（IAEA, 2015）和《通用安全指南》 第 2 部分《应用于核或放射应急的准备和响应准则》（IAEA, 2011）适用于核事 故或放射性应急情况中的饮用水，无论饮用水是否包装。这些标准适用于受影响 国家中用于消费的饮用水（见 2.1.4）。 1.2.7 饮用水中的天然放射性核素和人工放射性核素是否应采取不同的管理？ 不是。从饮用水中摄入放射性核素所致的辐射剂量并不取决于其来源。根据 健康风险评估的标准，GDWQ 不区分天然放射性核素和人工放射性核素。 但在风险管理方面存在差异，因为人工（即人为的）放射性核素通常在进入 供水点时是可控的。相反从周围的岩石和土壤进入供水的天然放射性核素通常难 以控制，如果超出了 GDWQ 中的标准值，这可能会影响所采取的措施。 1.3 WHO 采用的饮用水中放射性核素致公众健康风险的评估方法 1.3.1 GDWQ 用于评估饮用水中放射性核素致健康风险的指标是什么？ GDWQ 中用于评估饮用水中放射性核素致健康风险的标准是筛查水平、指 导水平和个人剂量标准（IDC）。氡不包括在这些标准中，需单独评估，见 1.6。 以下将更详细地论述其每一项标准。 GDWQ中的个人剂量标准 0.1 mSv/a是针对个人受饮用水中放射性核素长 期照射所致健康风险的评估，IDC 是供水和监管机构制定能够直接测量的 标准（即筛查水平和指导水平）的基础。 筛查水平作为饮用水监测的一部分是测量总放射性活度，以评估是否超过 IDC。筛查水平总 α 为 0.5 Bq/L、总 β 为 1 Bq/L（见 1.3.3）。如果超过任 何一种筛查水平，则应测定具体放射性核素的活度浓度，并将其与指导水 平进行比较，以确定是否超过 IDC。 指导水平是具体针对每个放射性核素，其活度浓度是根据假设全年饮用了 含该放射性核素的水、每天饮水量 2 升、所致年个人剂量 0.1 mSv（见 1.3.4）。 1.5.6 说明了如何使用指导水平来确定饮用水中存在的一种或几种放射性 核素是否超过 IDC。 各国的经验表明，绝大多数饮用水供应都遵从 GDWQ 中的放射性标准。 1.3.2 如何理解个人剂量标准 0.1mSv/a？ 个人剂量标准（IDC）是 GDWQ 中的一项用于评估受饮用水中放射性核素 长期照射所致健康风险的标准。0.1 mSv/a 的个人剂量标准代表了非常低水平的 健康风险 (见信息栏 1.6)。不管是天然还是人工放射性核素所致的 0.1 mSv/a 的 IDC 是指一年过程消耗的饮用水。IDC 在 GDWQ 中被转化为两个可操作的量， 即筛查水平和指导水平（见 1.3.3 和 1.3.4）。 6 信息栏 1.6: 关于 IDC 个人剂量标准（IDC）不应理解为饮用水不安全饮用的限值。饮用水是生活的基本要求， 没有饮用水供应的风险可能要比饮用不符合 IDC 标准的饮用水高得多。 1.3.3 使用筛查水平的目的及如何使用？ 筛查水平表达为总 α 和总 β 活度浓度的标准，低于此水平不需要采取进一步 行动，因为通常不会超过 0.1 mSv/a 个人剂量标准。 筛查水平使供水和监管机构能够以一种节省成本资源的方式评估饮用水中 的总放射性。建议使用筛查水平是因为测定饮用水中具体放射性核素过程费时、 费力且昂贵。而且在大多数情况下，饮用水中放射性核素的活度浓度极低，常规 监测的分析方法通常测不出来。 筛查水平总 α 放射性为 0.5 Bq/L，总 β 放射性为 1 Bq/L，这个筛查值涵盖了 饮用水中最常见的放射性核素对饮水所致的辐射剂量。这些筛查分析不涉及具体 的放射性核素。信息栏1.7讨论了当某个国家的剂量标准不同于0.1 mSv/a 的 IDC 并拟建立筛查水平标准时应该如何做。 如果超过任一筛查水平，应启动进一步调查（见 1.5.3）。1.5.3 的图 1.2 表 示了逐级应用筛查（和指导）水平的流程。 使用筛查水平时，必须了解以下情况： 总 α 和总 β 的测量是探测放射性核素发射的 α 粒子或 β 粒子，它们适用于 大多数情况下饮用水中可能发现的放射性核素。 然而有一些放射性核素无法用这些筛查方法来测量。1.4.3 提供了关于这 方面的更多信息，如果当地情况表明可能存在这些放射性核素时应采用的 方法。 某些天然放射性核素（特别是镭-228 和钋-210）即使未超过筛查水平，也 可能超过 0.1 mSv/a 的 IDC，某些情况下，仅这些放射性核素对总活度浓 度的贡献有意义。如果当地地质和水文资料表明可能存在这些放射性核素， 则应对具体放射性核素进行测量，并将其与指导水平进行比较。 信息栏 1.7: 根据不同于 IDC 的国家剂量标准来建立筛查水平 如果一个国家制定的国家剂量标准与 0.1 mSv/a 的 IDC 不同，并采用测量总 α 和总 β 作为筛查方法时，则需要确定不同的筛查水平，要考虑到饮用水中的放射性核素及其对剂量 的贡献，需征求专家意见。 1.3.4 使用放射性核素指导水平的目的及如何使用？ 放射性核素的指导水平是指如果全年以每天 2 升的量饮用了含该放射性核 素的水，所致年个人剂量为 0.1 mSv 时的活度浓度。如果已经确定饮用水中存在 几种放射性核素，则需要合并考虑，检查其加在一起不会超过个人剂量标准 0.1 mSv/a。来自地下水源的饮用水很可能就含有不同数量的天然放射性核素。1.5.6 提供了评估合并多种放射性核素后是否超过 IDC 的更多细节。 GDWQ 中提供了非应急情况下饮用水中广泛的最常见的天然放射性核素和 人工放射性核素的指导水平。最有可能在饮用水中出现的放射性核素的指导水平 见 GDWQ 汇总的表 9.2。其它的放射性核素见 GDWQ 的表 A6.1。在大多数情况 下，指导水平舍入到最接近的数量级，反映了计算指导水平时做出的保守假设。 7 指导水平应作为进一步调查的触发因素，而不应被解释为饮用水不安全饮用 的限值。指导水平是保守的，因为假设了饮用水是在这种活度浓度下全年每天饮 水量 2 升。实际上活度浓度在一年中常常发生变化，饮水的来源可能来自多种（例 如在家里、工作场所、学校、公共场所等）。 在具体情况下可以计算较为精准的指导水平，如 GDWQ 第 9 章所述，根据 当地或地区的饮水量。附件 1 提供了关于计算指导水平的进一步资料，包括对儿 童的计算。如果超过指导水平，由于在计算指导水平时采取了保守假设，调查所 采集的样本是否代表了一年中其它时间的情况、了解居民的饮水习惯都非常重要。 1.5.9 进一步详细说明了如果超过指导水平应如何做。GDWQ 中的指导水平不适 用于应急情况（见 1.2.5）。 1.3.5 指导水平是否需要针对儿童调整？ 不需要。由于指导水平不是饮用水不安全的限制，而是作为进行进一步调查 的依据，对于成年人来说，这个参数值是合适的。GDWQ 中采纳的评估方法在 计算指导水平时采取了保守假设。 如果超过了指导水平，就必须进行进一步调查，可能包括对受影响人群的具 体区域的评估，并考虑其饮用水消费习惯。在长时间超过指导水平情况下，则需 要对喝了由饮用水冲成的瓶装奶的儿童和婴儿进行剂量评估，这是因为儿童受某 些放射性核素的照射更敏感（反映在剂量系数不同），即使他们通常比成年人饮 水量少。 1.3.6 如何理解参考水平（1 mSv/a）？其与饮用水的个人剂量标准（0.1 mSv/a） 有何关系？ 国际基本安全标准（BSS）（IAEA, 2014）建议饮水所致辐射剂量参考水平 约为 1 mSv/a。这个参考水平表示了剂量或风险高于该水平被判定为不宜采取计 划照射，而低于该水平应根据辐射防护最优化原则开展计划照射以保证剂量可合 理达到尽可能低（ALARA）。不应将其视为可接受的剂量或剂量限值，如果可 能应努力减少高于参考水平的任何照射，直至低于参考水平。BSS 要求监管机构 根据饮用水中的放射性建立辐射剂量的参考水平，这与 GDWQ 方法相一致。 个人剂量标准（IDC）表示了一个极低的健康风险。大多数供水都遵从这一 标准并制定 0.1 mSv/a 的国家标准，符合大多数国家作为最优化原则（ALARA） 的一部分。然而在无法做到这一点的情况下，管理当局可为饮用水中高于 0.1 mSv/a （IDC）的放射性核素制定具体的参考水平（或国家标准）。而一般要根 据情况低于 BSS 的 1 mSv/a 参考水平（见 1.5.10）。 根据当时的情况并考虑到总体风险的平衡，包括没有饮用水供应的风险，可 能会出现允许选定人群的剂量高于 1 mSv/a 的情况。这样做的后果将是接受辐射 所致健康的风险可能稍微增高。 8 1.4 饮用水中放射性核素的测定 1.4.1 在供水系统链的哪个阶段应开展饮用水中放射性核素的测量？ 所进行的测量是否能够代表所消耗的饮用水十分重要。如果饮用水在饮用前 处理过，则应在处理后对水进行监测，因为处理可以降低许多放射性核素的活度 浓度。关于水处理有效性的更多信息见 3.2。一般而言，在水的输送系统中放射 性核素的浓度不会变化（氡除外，见 1.6），因此适合在处理后的处理厂或输送 前的储水库取样测量。对于未处理的供水，例如一些小型供水，可以测量水源或 取水处的放射性核素。理想情况下应在消费地点（即水龙头和公共取水处）进行 一些测量，然而这通常不易实行。 对于新的供水，应在水源处测量水中的放射性核素，以确定其是否适合作为 饮用水水源（更多信息见 1.4.2），还应考虑水处理的程度（见 3.2）。应与评估 微生物和化学物的风险一起进行，作为制定水安全计划的一部分。 1.4.2 饮用水中放射性核素的测量频次应如何？ 确定测量饮用水中放射性核素活度浓度的频次，要综合考虑饮用水中放射性 核素对公众潜在的健康风险、可利用的水资源以及提供安全饮用水的其它预先考 虑，包括分析微生物和化学污染物的分析等。 一般来说，在设计和建造新的供水系统之前，应进行采样并分析放射性核素， 以确定其作为饮用水的适用性。测量放射性核素活度浓度随季节性的变化非常重 要，第一年需要足够的频次，通常一年中至少有四次（即每季度一次）以显示任 何季节性的变化。理想情况下，除了要测量总 α 和总 β 活度外，还应测量具体放 射性核素，尤其预期可能存在天然性放射性核素的情况。 由于地下水中放射性核素水平差异大，有必要考虑对新的供水（包括新的抽 水点）进行监测；即使已经有关于地下水源的信息，或已了解该地区相似的地下 水资源和潜在地质情况，也应开展监测。 现有供水的取样频次应与这几个因素关联起来：水中活度浓度的水平；水源 （即地表水或地下水）以及一年中活度浓度可能变化的情况（例如地下水源可能 比地表水源可变性小)；供给的人口数量；历史监测记录的数量和质量情况。在 确定频次时，还应考虑以下几点： 如果活度浓度低于筛查水平且稳定，与相关监管机构以及卫生和水主管部 门商定，可将监测频次降低至每两至五年一次（或者更长），取决于水源 情况。 如果总活度浓度接近筛查水平，具体放射性核素的活度浓度接近指导水平， 或者测量多个放射性核素，所测具体放射性核素的浓度其总比值接近总的 指导值（见 1.5.6），采样频次应保持甚至增加。 在下列情况增加取样频次： a. 测量结果表明活度浓度有上升趋势； b. 残留放射性物质的区域，且这些区域从未受到监管控制； c. 在核或放射应急情况发生后，存在放射性核素残留的地区； d. 如果附近可能存在放射性核素污染源，或预期随着时间推移活度将迅 速变化（例如采矿活动或核反应堆）。 9 如果活度浓度始终超过筛查水平，则需要进一步调查，包括进一步测量 并可能增加采样频次（见 1.5.3）。 关于制定采样方案可参考国际标准（ISO, 2006）。饮用水监测方案的一些 实例见信息栏 1.8。 信息栏 1.8：饮用水监测方案实例 德国 德国的饮用水条例（BMG, 2016）要求监测饮用水中放射性核素。进行初步分析后以确 定和评估公共供水中的年平均活度浓度，包括： • 现有的饮用水供应：四年内对四个不同季度进行的四次分析； • 新建的饮用水供应：在一年内在四个不同季度进行的四次分析。; • 如果初步分析显示放射性物质超过一个或多个指导值，则有必要进行定期分析。 日本 2011 年 3 月日本福岛第一核电站事故发生后，对饮用水中铯-134（134Cs）和铯-137（137Cs） 进行了监测，由于在自来水中检测到放射性铯，监测工作一直持续到事故初始应急阶段之后 （MHLW，2011）。推荐的监测频次已在应急阶段每天至少一次逐渐地减少到每周一次， 截止到 2012 年 4 月至少每月一次，再到每一个多月测量一次 134Cs 和 137Cs（MHLW, 2012a; 2012b)。目前仍有几家供水机构不时地测量放射性铯（截至 2018 年 1 月），以确保饮用水 中的放射性处于安全水平。 美国 在美国，向至少 15 个服务点或 25 个人（使用饮用水一年）提供饮用水的供应商必须在 启动运行后或启动使用新水源后，第一年每个季度在供水的入口处采集水样监测。初始的监 测结果决定了今后监测的频次： 1. 如果初始监测结果低于检测限，每个采样点的监测频次为每 9 年一次； 2. 如果初始监测结果大于检测限，但小于最大污染物限值的一半，监测频次减少为每 6 年一次； 3. 如果初始监测结果大于最大污染物限值的一半，但小于最大污染物限值时。监测频 次为每 3 年一次； 4. 如果初始监测结果大于最大污染物限值，需要每个季度在每个采样点采样分析。 可根据同一供水的不同污染物与四个最大污染物水平中的每一个进行比较的结果，对不 同污染物建立不同的监测频次，如：同一个供水系统可能需要每三年取样一次检测总 α 放射 性，而每六年取样一次检测铀，这分别取决于总 α 放射性和铀的初始监测结果。 约旦 约旦的 Disi 输水项目（详细信息见 4.3 案例分析部分），定期监测水井和用户水龙头之 间供水链各点水中的放射性核素水平。供水机构和卫生局遵循一项监测协议，要求在每个商 定的取样点设置以下频次： 1. Disi 输水项目对 55 口井进行季度性采样，以评估放射性核素活度浓度随时间的变 化趋势，两年后频次降低到每年一次； 2. 约旦南部 55 口水井合并的集水槽中的水，在进入 320 公里长的主输送管之前，每 月取样分析； 3. 在安曼两个水输送点混合之前，每月对 Disi 混合水进行取样； 10 4. 每年监测用于混合的低活度浓度水（取自于 ZaraMa'en 和 Zai 处理厂的水，其总 α、 总 β、镭-226 和镭-228 的历史监测结果始终低于方法检出限）； 5. 在安曼主要水库的出口处，每月测量混合后的饮用水样本。 6. 每月测量水库公用水的样本，代表安曼不同配水区向消费者供应的水。 1.4.3 是否有总 α和总 β标准筛查方法检测不到的放射性核素？ 总 α 测量可检测出饮用水中可能存在的所有发射 α 粒子的放射性核素。 标准的总β测量可检测出非应急情况下饮用水中可能存在的发射 β粒子的大 多数放射性核素。但有一些放射性核素无法通过总 β 的标准测量方法检出，要么 因为其不发射β粒子、要么因为发射的β粒子能量太低而无法用该方法有效检出。 总 β 方法检测不到的放射性核素值得注意的有氚、碳-14 和硫-35（信息栏 1.9 提供了在欧洲要求监测氚的一个实例）。某些气态或易挥发的放射性核素， 例如碘的同位素也不会被检出，因为在分析过程中这些放射性核素会发生损失。 不过这些人工放射性核素大部分情况下未必需要进行常规分析。 值得注意，可能会低估天然放射性核素铅-210（210Pb）和镭-228（228Ra）的 活度浓度。由于其 β 能量较低，其探测效率相对很低，信息栏 1.10 中有一个实 例讨论。在比较少见的情况下，这些放射性核素是总活度浓度最重要的贡献者， 可能不超过筛查水平但超过个人剂量标准（IDC）0.1mSv/a。如果认为可能存在 这些核素，就要具体开展这些放射性核素的分析。综合考虑该地区的地质、水文 以及放射性核素在岩石、矿物、土壤中的含量情况，还有历史数据情况以确定这 些放射性核素在地下水中的范围。 信息 1.9：欧盟饮用水水质指令中要求监测氚 欧盟饮用水水质指令（EC, 2013）要求，供水的水源地区存在人工来源的氚或其它放射 性核素，并且无法通过其它监测或调查显示氚的水平低于参考值 100 Bq/L 时，成员国要监 测水中的氚，如果氚的浓度超过该参考值，要求开展调查是否存在其它人工放射性核素（EC, 2013）。 有关测量方法的更多信息，见 3.5 节。饮用水中氡的测量在 1.6 节。 信息 1.10：约旦监测 228Ra 约旦的 Disi 输水项目，定期监测水井和用户水龙头之间供水链各点水中的放射性核素 水平。在已知 228Ra 是主要的放射性核素后，开展镭同位素分析和剂量估算，总 β 法可能检 测不到该放射性核素。在约旦很多测量结果中总 β 活度浓度小于或约等于 1 Bq/L，但测得 228 Ra 的活度浓度高于指导值 0.2 Bq/L（未舍入值），因此个人有效剂量> 0.1 mSv/a（使用 GDWQ 中关于饮水量的默认值）。 11 1.5 GDWQ 方法如何应用于饮用水中的放射性核素 1.5.1 如果一个或少数几个饮用水样品超过筛查水平，这是否意味着辐射剂量将 大于个人剂量标准 0.1 mSv/a？ 不是。超过总 α 筛查水平或总 β 筛查水平任何一项并不一定表示将会超过个 人剂量标准（IDC）0.1 mSv/a，IDC 是年剂量标准，因此如果单个甚至少数几个 饮用水样本中的总活度浓度在短时间内超过筛查水平，这并不一定意味着将超过 IDC。如果超过任何一个筛查水平，则有必要进一步调查有关情况，例如进一步 取样（见 1.5.3）。 1.5.2 如果未超过筛查水平，是否需要采取任何措施? 如果总 α 和总 β 均未超过筛查水平，饮用水的常规监测将持续按照水质监管 机构已同意的地点和频次执行。在绝大多数情况下，不会超过个人剂量标准（IDC） 0.1 mSv/a；但有两种不常见的情况除外。 首先是怀疑水中可能含有一种无法通过筛查方法检测到的放射性核素。 1.4.3 中提供了一些总 α 和总 β 筛查方法无法检测的人工放射性核素的信 息。有其他信息来源表明饮用水中可能存在不会被检测到的放射性核素， 例如水源集水区的环境监测数据，场址可能引起的放射性核素流出物到 集水区以及当地的地质情况等。 第二是对总活度浓度影响最大的放射性核素无法通过筛查方法有效地检 测出来。如 1.4.3 所述，镭-228（228Ra）和钋-210（210Po）很值得注意， 见信息栏 1.11，有关饮用水中 228Ra 对剂量贡献最大的示例。 在这些情况下，应进行放射性核素测量，并与相关指导水平进行比较（见 1.5.3）。 信息栏 1.11:饮用水中 228Ra 的放射性核素活度浓度对剂量贡献最显著的举例 约旦：2013 年 10 月至 2015 年 5 月期间的 Disi 井水测量 226 Ra：0.31–0.47 Bq/L 228 Ra：1.07–1.41 Bq/L 210 Pb：0.02 Bq/L 浓度随时间一直保持稳定。 澳大利亚昆士兰：考虑 110 钻孔对蓄水层的影响（1.7百万平方公里）（Kleinschmidt, Black & Akber, 2011） 226 Ra：平均值 0.07 Bq/L（0.01–0.96 Bq/L） 228 Ra：平均值 0.14 Bq/L（0.01–2.8 Bq/L） 238 U：平均值 0.15 Bq/L（0.04–0.71 Bq/L） 1.5.3 如果饮用水样品超出任一筛查水平，需要采取什么进一步措施？ 如果超过了总 β 筛查水平，则应单独测定饮用水中的总钾量后，从测量中减 去钾-40 的贡献（见 1.5.4）。 如果超过任一筛查水平（已扣除钾-40 对总 β 的贡献），则应通过重复测量 来确认结果的有效性，如果原始饮用水样品有剩余，可以进行重复测量。 12 一旦确定了最初的测量结果，接下来是对饮用水中的总 α/总 β 活度浓度进行 进一步测量，需要这些来评估该情况以及是否会随时间变化。理想情况下，最初 几周至少应每周取样分析。应采集足够量的样品，以便必要时可以在以后开展具 体放射性核素的分析。 如果测得的总活度浓度持续超过筛查水平，则应至少连续几个月的时间进行 取样。这需要了解可能存在的季节性变化，因为长时间内，平均的活度浓度可能 不会超过筛查水平。除非水源非常稳定，否则放射性核素的时间变异性可能差异 很大，如果对放射性核素的排放没有得到控制或发生未经授权的排放，则可能出 现较大变化。监测所持续的时间将取决于水源的特性及持续监测的结果。 如果在最初测量超出了筛查水平，之后在定时间内进行的进一步测量又低于 筛查水平，则无需进一步干预。除了例行监测计划外，可能还需要偶尔采样，例 如增加比正常高的频次，以确保放射性核素保持在低水平。 如果始终超过筛查水平，则需要确定水中存在的放射性核素。应开展放射性 核素分析以确定其否存在以及在饮用水中的活度浓度。应研究放射性核素的可能 来来源并制定具体的分析策略。图 1.2 中举例说明了该过程。 13 图 1.2 饮用水中放射性核素测量流程图 1.5.4 当总 β 活度浓度超过筛查水平时，从中扣除钾-40 贡献的原因是什么？如 何执行？ 总 β 的测量包括了钾-40（40K）的贡献。钾-40 是发射射线的天然放射性核 素并与稳定钾有一个固定比值，钾是调节人体很多功能的一种必不可缺的元素， 人体内钾的含量通过生理过程保持稳定，所以体内的 40K 是自然调节并不会累积， 而是维持在一个恒定水平，与摄入多少无关。因此如果总 β 超过筛查水平，必须 考虑扣除 40K 对所测量的总 β 活度浓度的贡献。 测量总 α 和总 β 的活度浓度 是否超过总 β 标准？ 是否超过总 α 标准？ 进行常规监测 进行常规监测 检查所测量方法的有效性 查找潜在放射性核素的源项信息并制定分析 计划，开展放射性核素分析。 根据指导水平检查所测的浓度，使用 1.5.6 中 所述的求和方法检查是否超过了 IDC 返回常规监测。为消除疑 虑，考虑增加测量频次数月 否 是 是 是 是 否 否 14 采用放射性核素测量技术来分析饮用水样品中钾-40 的浓度是不切实际的， 因为其发射低能射线，况且从溶液中化学分离放射性核素较困难。由于钾-40 与稳定钾之间的比值固定，40K 的 β 活度可以根据总钾 27.9 Bq/g 的系数计算，该 公式见信息栏 1.12。 信息 1.12：水中 40K 的计算 水样中的 40K（Bq/L）=水样中总钾（g/L）×27.9 1.5.5 如何识别饮用水中哪些放射性核素导致超出筛查水平？ 如果总 α 或总 β 任何一个超过筛查水平，其结果的正确性已被确认，通过其 它的测量也超过了筛查水平（总 β 测量已扣除钾-40）（详见 1.5.3 和 1.5.4），则 饮用水中具体放射性核素的贡献需要确认。当决定对超过筛查水平的水样判定是 哪些放射性核素可能所致时，应考虑所有相关信息，信息来源包括该区域和水源 集水区的环境监测数据，场址可能引起的放射性核素流出物到集水区的相关知识 以及当地的地质情况等。放射性核素的来源极有可能是天然来源，比如镭-226 和镭-228；也可能存在人工放射性核素，如钴-60、锶-90 以及铯-137。 1.5.6 如果测量饮用水中具体放射性核素超过个人剂量标准 0.1 mSv/a 将如何评 价？ 放射性核素的指导水平，是指全年每天饮水量 2升所致的 0.1 mSv 个人剂量。 如果在饮用水中仅测出一种放射性核素，则应将其活度浓度与该放射性核素的指 导水平进行比较（见 GDWQ 第 9 章中的表 9.2，以及下表 1.1 概述的常见放射性 核素；其它放射性核素见 GDWQ 附件 6 的表 A6.1）。如果超过指导水平，则很 有可能已经超过了个人剂量标准（IDC）的 0.1 mSv/a，需要进一步的调查（见 1.5.9）. 表 1.1 饮用水中常见放射性核素的 WHO 指导水平汇总 放射性核素 指导水平（Bq/L） 3H 10 000 14C 100 90Sr, 131I, 134Cs, 137Cs, 238U* 10 226Ra, 228Th, 230Th, 232Th, 234U*, 239Pu, 241Am 1 210Pb, 210Po, 228Ra 0.1 *铀通常根据其化学毒性加以控制；WHO 关于饮用水中铀总含量的指导值为 30g/L，相 当于 238U 或 234U 的 0.37Bq/L。 关键核素：氚（3H）、碳-14（14C）、锶-90（90Sr）、碘-131（131I）、铯-134（134Cs）、 铯-137（137Cs）、铀-238（238U）、镭-226（226Ra）、钍-228（228Th）、钍-232（232Th）、 铀-234（234U）、钚-239（239Pu）、镅-241（241Am）、铅-210（210Pb）、钋-210（210Po） 和镭-228（228Ra）。 如果已识别出多个放射性核素，则需要考虑所有放射性核素的总和，以确保 其不超过 IDC，使用的公式为： 此处： 15 Ci =测量的放射性核素 i 大于其检测限（LOD）的活度浓度 GLi=放射性核素 i 的指导水平，采用了默认的饮水量（成年人 2 L/d）计算 （见信息栏 1.13 的理论示例)。 信息栏 1.13：针对 IDC 评估饮用水样品中的活度浓度理论示例说明 测量的活度浓度如下： 镭-226 = 0.8 Bq/L 镭-228 = < LOD 铅-210 = 0.05 Bq/L 钋-210 = 0.03 Bq/L 求和方程 = 0.8/1 + 0.05/0.1 + 0.03/0.1 = 1.6 因为总和大于 1，所以超过了 0.1mSv/a 的 IDC。 如果总和≥1,很可能已经超过了 IDC，则需要进一步调查（见 1.5.9）。如 1.3.4 中所述，GDWQ 中的指导水平为舍入到最接近的数量级。此调查的一部分是检 查使用这些舍入的指导水平是否过于保守（见 1.5.9）。 要小心如果这些采用的测量方法与指导水平相比低于 LOD 的报告（信息栏 1.14 提供了瑞典关于此问题的示例）。这些测量方法不是给出实际的活度浓度， 而是所用设备检测能力的特征。报告中使用的方法<LOD 对于饮用水中的实际活 动浓度将是保守的；样品中可能存在放射性核素，但所用设备无法定量。 信息栏 1.15 给出了在应用欧盟饮用水水质指令时判定是否超出 0.1 mSv/a 剂 量标准的方法（EC，2013）。 信息 1.14：与指导水平进行比较时解释 LOD 的示例 在瑞典，将欧盟饮用水水质指令（EC, 2013）纳入国家标准时，建议如果活度浓度低于 LOD，将在总和（剂量计算）中不考虑这些放射性核素。该指令中要求的 LOD 值非常低（见 3.5 部分的信息栏 3.6）。 信息 1.15：欧盟饮用水水质指令中是否超过 IDC 的识别 欧盟饮用水水质指令（EC, 2013）中使用的识别是否超出 0.1 mSv/a 剂量标准的方法与 GDWQ 的非常相似（EC, 2013）。给出的活性浓度为指导水平的 20％，这些值可以视为需 要进一步调查的水平。如果所测得的活动浓度均未超过这些“触发水平”，则无需进行更复杂 的放射性核素加总过程检查是否已超过 IDC。 1.5.7 如果饮用水中所测放射性核素的活度浓度未超过指导水平，这是否意味着 无需采取进一步措施？ 是，在许多情况下。如果在饮用水中测定出一种放射性核素且未超出指导水 平，则几乎不可能超过 0.1 mSv/a 的个人剂量标准（IDC）。应当在国家饮用水 规程中所设置的地点和频次继续开展饮用水放射性监测。 如果已测定出几种放射性核素，但单独测得的活度浓度均未超过所测放射性 核素的指导水平，则需要考虑整个放射性核素的总和不超过，这个确定按 1.5.6 的方程式。如果总和≥1，则可能会超出 IDC，需要进一步调查（见 1.5.9）。 但有一个不常见的例外情况，即使总和1，如已确定放射性核素铀-238、镭 -226 或锶-90 中的任何一个对剂量贡献很显著，则可能会低估年剂量。这是因为 16 这些放射性核素的指导水平舍入值接近 10，其活度浓度将高于所致 0.1 mSv/a 的 IDC 两倍或更多（见 1.5.9 的表 1.2）。 1.5.8 如果超过了 0.1 mSv/a 的个人剂量标准，是否表示饮用水不适合饮用？ 不是。超过个人剂量标准（IDC）并不表示饮用该饮用水不安全。如果所测 饮用水中的放射性核素，按通常假设表明超过了 IDC，需要采取其它措施开展进 一步调查，见 1.5.9。0.1 mSv/a 的辐射剂量表示非常低的健康风险，并且通常比 公众所受接受所有辐射源的剂量低至少 20 倍。此外，该剂量标准比国际基本安 全标准（BSS）推荐的饮用水中的放射性核素参考水平低 10 倍（IAEA, 2014）。 如果年剂量在 BSS 推荐的参考水平 1 mSv/a 附近（见 1.3.6），尤其在没有 其它可供使用或不适合和负担不起的替代水源时，不应该自动停止饮用水供应。 在这些情况下，考虑到总体风险的平衡，包括没有饮用水的风险，允许选定人群 的剂量高于 1 mSv/a，其结果将是放射风险可能略有增加。 需要重要说明的是，即使因为放射性核素水平供水被认为不适合人群饮用， 它仍适用于如清洗和去污。 1.5.9 如果超过了指导水平或放射性核素的总和超过了 0.1 mSv/a个人剂量标准， 下一步该怎么办? 饮用经计算摄入的辐射剂量在 0.1 到 1 mSv/a 之间的水不被视为有放射性健 康风险（见 1.3.6 和 1.5.8）。但如果超过了 0.1 mSv/a 的 IDC，有必要进行优化 以尽可能合理地减少饮用水源的长期照射。国家和地方当局需要对情况进行彻底 调查，在决定采取何种措施时，关键的考虑因素是超出 IDC 的程度。如果评估 的剂量低于国际基本安全标准（BSS）规定的 1 mSv/a 的参考水平，则无需采取 任何应急措施。 这个回答是基于已经超过了 GDWQ 中的 IDC 而写。各国可以制定不同的饮 用水标准或参考水平（见 1.5.10）；然而如果超过该国的国家标准/参考水平，这 里给出的逐步方法将相同。 步骤 1 使用非舍入的指导水平值来计算 IDC GDWQ 中的指导水平是舍入到最接近的数量级，以反映该方法的筛查性质， 在大多数情况下，指导水平的计算所做出的假设偏保守。表 1.2 给出了 GDWQ 中的指导水平，将其舍入到最接近的数量级，以及给出了实际活度浓度。使用 GDWQ 指导水平可能会导致这样一种情况，即计算出的 IDC 超出 0.1 mSv/a，但 实际上的辐射剂量低于 0.1 mSv/a（信息栏 1.16 提供了一个理论示例，信息栏 1.17 提供了一个巴西的示例）。 17 表 1.2 常见放射性核素的指导水平 指导水平 核素 半衰期 舍入值 Bq/L 未舍入值 Bq/L 3 H 氚 12.5 a 10 000 7 610 14 C 碳-14 5 730 a 100 240 90 Sr 锶-90 29.12 a 10 4.9 131 I 碘-131 8.04 d 10 6.2 134 Cs 铯-134 2.062 a 10 7.2 137 Cs 铯-137 30 a 10 11.0 210 Pb 铅-210 22.3 a 0.1 0.2 210 Po 钋-210 138.38 d 0.1 0.1 228 Ra 镭-228 5.75 a 0.1 0.2 234 U 铀-234 244 500 a 1 2.8 238 U 铀-238 4.468 x 109 a 10 3.0 228 Th 钍-228 1.913 a 1 0.6 230 Th 钍-230 7.54 x 104 a 1 0.7 232 Th 钍-232 1.405 x 1010 a 1 3.0 239 Pu/ 240 Pu 钚-239/240 2.41 x 104 a/6537 a 1 0.6 241 Am 镅-241 432.2 a 1 0.7 *根据对数刻度值的平均值，指导水平舍入到最接近的数量级（如果计算值低于 3×10n，则为 10n；如果 值为 3×10n或以上，则为 10n+1）。 信息栏 1.16: 检查放射性核素总和是否超过 1 的理论实例 测量的活度浓度为: 铀-234 = 0.07 Bq/L 镭-228 = 0.05 Bq/L 铅-210 = 0.03 Bq/L 钋-210 = 0.03 Bq/L 使用 GDWQ 中指导水平的舍入值（见表 1.2）: 求和方程 = 0.07/1 + 0.05/0.1 + 0.03/0.1 + 0.03/0.1 = 1.17 在这种情况下，求和>1，超过了 0.1mSv/a 的 IDC。 使用非舍入值的活度浓度（见表 1.2）： 求和方程 = 0.07/2.8 + 0.05/0.2 + 0.03/0.2 + 0.03/0.1 = 0.725 在这种情况下，求和小于 1， 没有超过 0.1mSv/a 的 IDC。 18 信息栏 1.17: 巴西地下水中放射性核素的浓度（见 4.1 节） 巴西地下水井中放射性核素的几何平均浓度 核素 浓度(Bq/L) Ci/GL a,b 指导水平（GL） 舍入值 Ci/GL a,b 指导水平（GL） 非舍入值 238 U 0.013 0.0013 0.0043 234 U 0.045 0.045 0.016 230 Th 0.007 0.007 0.01 226 Ra 0.015 0.015 0.03 228 Ra 0.06 0.60 0.30 232 Th 0.0002 0.0002 0.00007 210 Po 0.030 0.30 0.30 210 Pb 0.04 0.40 0.20 求和 1.37 (> 1) 0.86 (< 1) a 指导水平来源于表 1.2 b “黑体字”标注的值表明使用非舍入值 Ci/GL 较低。 关键核素：铀-238（238U）、镭-226（226Ra）、钍-228（228Th）、钍-230（230Th）、铀-232（232U）、铅-210 （210Pb）和镭-228（228Ra）。 步骤 2 –进行更详细的剂量评估 更详细的评估应同时考虑被调查的供水的特点和饮用饮用水的实际人口。对 供水和水源的监测将提供有关水中放射性浓度稳定性的信息，以及它们全年是否 由于自然过程而波动，或者放射性核素流出物向地表水源排放量较大的波动。可 以考虑进一步测量以确定对剂量贡献最大的放射性核素活度浓度的波动，特别是 在筛查阶段没有做该部分的（见 1.5.3）。 剂量评估必须使用一年中的平均剂量。 有可以使用的数据或具有足够能力承担此项分析，国家饮水量的估量可用于 计算指导水平，而不必使用 GDWQ 中的指导水平，后者是基于 2 升/天饮水量的 默认假设。还应酌情考虑评估用饮用水冲调的瓶装牛奶对儿童和婴儿的剂量（附 件 1 提供了有关如何计算对儿童剂量的信息）。 步骤 3 –考虑降低饮用水中活度浓度，包括水处理(见 1.5.11) 对于经过第 1 步和第 2 步确认已超过 IDC 的饮用水供应，国家主管部门应 考虑采取补救措施以减少饮用引起的健康风险，根据可用资源和 IDC 的超限程 度，将饮用的水量尽可能降低。 应审查任何现有的水处理方法，以查看是否可以通过直接实施或变更处理来 实现进一步的减少（见 3.2）。实施新的水处理或对现有的水处理进行重大改变 是一项重大任务，尤其是对于未经处理或仅经过消毒的地下水，必须谨慎进行， 以免增加饮用水供应对健康的其他危害。 停止将水用于饮用目的必须考虑整体利益的合理性。做出停止决定时，要考 虑的因素包括超出参考水平的程度，修复成本以及其它供水的可用性。在不确保 消费者可以使用另一种更安全选项的情况下，中止供水是不合适的。 根据个人剂量水平所建议采取措施的汇总见表 1.3。 19 表 1.3 根据个人剂量水平建议采取措施的汇总 饮用水所致的个人剂量, mSv/a 干预/措施 < 0.1 不需要采取行动。 0.1–1 调查超过 IDC、国家标准或参考水平的情 况。行动应与超出剂量标准/放射性健康风 险和可用资源情况相称。 基于放射性健康风险，限制饮用水供应的使 用是不合理的。 如果可能，减少剂量。 > 1 调查超过国家标准或参考水平的情况。 应根据具体情况采取行动，行动应与超出剂 量标准/放射性健康风险和可用资源情况相 称。 可以根据放射性健康风险考虑限制使用饮 用水供应，但平衡整体风险很重要，包括没 有饮用水供应的风险。 如果可能，减少剂量。 1.5.10 基于 GDWQ 和基本安全标准建立国家标准的考虑因素是什么？ 对于可以控制的非应急情况，防护策略应与相关的辐射风险相称。如 GDWQ 中所述，国际基本安全标准（BSS）要求监管机构根据饮用水中放射性所致的辐 射照射建立参考水平，其有效剂量应不超过 1 mSv/a。在建立国家参考水平时， 需要将当前的技术、经济、环境和社会情况作为优化过程的一部分。每种情况都 会有所不同，在做出最终决定时，必须考虑没有放射性因素例如补救成本和其它 饮用水供应的可用性。对于不存在地下水中天然放射性核素水平较高的大多数国 家，建立 0.1 mSv/a 的国家标准是合适的。如果地下水中天然存在的放射性水平 较高，而替代水源或水处理的选项最少，则针对受影响的人群，高于 0.1 mSv/a 但小于 1 mSv/a 的值也合适。 对于选定人群，可能会出现允许高于 1 mSv/a剂量的情况，根据当时的情况， 考虑总体风险的平衡，包括没有饮用水的风险，在不确保消费者可以使用另一种 更安全的选择的情况下，中止供水是不合适的。 根据 BSS 和 GDWQ 推荐与要求建立国家标准或参考水平见框架见表 1.4。 表 1.4 制定国家标准或参考水平的框架 饮用水所致的个人剂量, mSv/a 国家标准/参考水平 < 0.1 设置个人剂量标准（IDC）（0.1 mSv/a）。 （须采用 GDWQ 中包含的操作值，表示 为筛查和指导水平） 0.1–1 设置在 0.1–1 mSv/a 之间，与 GDWQ 和 BSS（见 1.3.6）一致。（GDWQ 中包含的 操作值，表示为筛查和指导水平，将需要 进行调整） 20 > 1 根据具体情况进行设置。可以设置为>1 mSv/a，取决于当时的情况并考虑到整体 的平衡风险，包括没有饮用水供应的风险。 标准/参考水平> 1 mSv/a 仅适用于受影响 的人群。一种选择是建立临时标准/参考水 平，以便有时间达到较低的值。（GDWQ 中包含的操作值，表示为筛查和指导水平， 需要进行调整） 在建立国家标准/或参考水平时，主管当局应考虑以下因素： 了解在放射性核素可移动的岩石/地下水蓄水层中，导致高天然放射性水 平的地质区域（见信息栏 1.18 举例）； 对将地下水用于饮用水供应的地点进行人口加权调查； 确定供水是否经过处理或可进行处理（考虑到实施新的水处理或对现有 水处理进行重大更改是一项重大任务，并且在许多资源匮乏的环境中不 可行）； 确定是否有替代供应； 建立饮用水中放射性核素的监测计划，以识别任何健康风险，并将其与 供水中的其它风险（即微生物和化学风险）结合起来，并考虑可用资源； 制定计划，以提高公众和利益相关者对饮用水中放射性核素低健康风险 的认识，尤其是在已经确定活度浓度超过指导水平和 IDC 的情况下。 信息栏 1.19 给出了设立饮用水的参考水平和国家标准示例。 信息栏 1.18：澳大利亚昆士兰州地下水中放射性核素分布举例 制定了一项筛查计划以提供有关地下水供应的放射水平和范围的原始数据。采样旨在包 括尽可能多的蓄水系统，尤其是为社区服务的系统。选择的采样区域覆盖昆士兰州水利委员 会提供的蓄水层岩性指标，覆盖面积约为 170 万平方公里，因此开发了一个采样工具包并随 调查表邮寄。接收了 110 个钻孔的样品（185 个点中的 59％），并对一系列天然放射性核素 进行了分析。更多详细信息见 Kleinschmidt，Black＆Akber（2011）。 信息栏 1.19: 设定饮用水参考水平和国家标准的示例 日本 日本福岛第一核电站事故发生后，从 2011 年 3 月至 2012 年 3 月，暂定了限制自来水摄入量 （用于饮用和烹饪）的临时管理指标值为碘-131（成人 300 Bq/L，婴儿 100 Bq/L）、放射性 铯（200 Bq/L）。自 2012 年 4 月 1 日起，建立“自来水中放射性物质管理的标准水平”，放 射性铯（包括铯-134 和铯-137）为 10 Bq/L，替代了先前作为应急的临时管理指标值，并应 用于长期的非应急情况。此水平直接由 GDWQ 中的指导水平导出（不必设置碘-131 的指标 值，因为该放射性核素由于其很短的半衰期-约八天，而不再受到关注）。 约旦 在约旦，调查发现 Ram 含水层（与可利用的含低放射性的水资源使用前先混合）的平 均剂量在 0.65-0.75 mSv/a 之间，镭-228 占总剂量贡献的 70％至 85％。在考虑了 WHO 的 GDWQ 中的指导，并仔细审查了当地的环境、社会和经济状况之后，约旦将饮用水标准中 21 的参考水平从 0.1 mSv/a 提高到 0.5 mSv/a。基于评估认为新的参考水平是合理的，该评估认 为潜在的健康风险是可以承受的，而健康净收益超过了潜在的健康风险。 巴西 巴西饮用水的监管机构-巴西核能委员会，在其饮用水法规中采用了以下标准。 参考水平 (1 mSv/a) 国家参考水平 饮用水的总剂量应低于国家参考水平 1 mSv/a。 优化范围 (0.1–1 mSv/a) 尽可能采取防护措施以将剂量保持在合理可达 到的最低水平。实际上不能达到标准 0.1 mSv/a 的 IDC 情况下，如果总剂量高于 0.1 mSv/a 且低 于参考水平 1 mSv/a，将不采取措施。 调查水平 (0.1 mSv/a) 此水平不能解释为饮用水不安全的限值，而是作 为进一步调查的触发条件。 巴西核能委员会将单独建立一项条例，包括当总和总超过筛查水平时的剂量计算 过程。 1.5.11 降低饮用水中放射性核素活度浓度有什么可能的选项？ 在超过个人剂量标准（IDC）或国家设定的参考水平情况下，应检查降低饮 用水中活度浓度的可用选项。所考虑采取的补救措施计划，应首先证明任何策略 都是合理的，可以实现净收益并且总体上要利大于弊，并且辐射风险与其它风险 （例如微生物，化学污染物）相当。 下面简要讨论可以考虑的主要选项。选择的方案取决于具体情况，选择方案 时要考虑的因素包括超出 IDC 或参考水平的程度，方案的成本以及其它饮用水 的供应情况。 此处提供的信息具有一般性，针对特定情况需要对选项进行全面评估。 提供可替代的供水。有可能改用替代水源，例如从地下水源变为地表水 源，不会导致如此高浓度的天然放射性核素的地下水源。还要确保水源 的变化不会导致无法控制或难以控制的其它更大风险的引入（例如地表 水源经常受到更多污染，尤其受到微生物的污染）。 供水的可控混合。如果有多于一种供水可应用于水的处理或后期处理， 则可以将所关注的饮用水与不含放射性核素或含有较低浓度的放射性核 素的水混合。这是降低饮用水中活度浓度的有效方法，并且具有不会额 外产生放射性废物的优点（见信息栏 1.20 示例）。混合法对小型个体供 水和集中供水不实用。 对现有水处理技术进行改进。结合絮凝、沉淀和砂滤工艺处理地表水， 可以去除水源中约 30％至 100％的悬浮放射性核素。离子交换过滤特别 适用于地下水源，对于天然存在的镭和铀可以去除 70％以上。有关常见 水处理过程对放射性核素的去除能力的更多信息见 3.2 部分。可用于帮 助确定是否实施额外的水处理检查表的示例，美国 EPA 第 I 部分（2005） 给出了开展水处理最合适和可行的方案。实施新的水处理或对现有水处 理进行重大更改可能是一项重大任务。 —水处理通常会产生废物，其中将包含从水中去除的放射性核素（见 3.3）。 —商业化水处理设备可应用于家庭或私人场所以减少饮用水的放射性污染，其包 括用于软化水的水过滤系统、载有离子交换材料的碳过滤器（罐式过滤器）和小 22 型反渗透装置，这些产品应经过相关标准化组织认证。家庭水处理方案会产生含 有从水中去除的放射性核素的废物（见 3.3）。 信息栏 1.20: 混合供水的示例 约旦 在约旦，考虑了以下补救措施，以解决 Disi 输水项目供应中超出国家参考水平的情况： 混合、反渗透、纳米过滤、石灰软化、选择性树脂的离子交换以及电渗析。对于每个替代方 案，均进行了中试规模的可行性研究。经过对 Disi 输水项目 108 m3/a 的全程回收的补救考 虑，在环境和成本效益分析考虑后，决定最实用且可持续的方案是混合水以得到可用的低放 射性水资源。混合后使年剂量从约 0.7 mSv 减少到约 0.4 mSv（详细信息见 4.3 部分）。 加拿大 加拿大里贾纳市的饮用水取自 Buffalo Pound 湖，Buffalo Pound 水处理厂于 1955 年投入 使用，在此之前，所有水都来自铀浓度较高的深井，高于全国平均水平。自 1960 年代以来， 越来越多的 Buffalo Pound 湖地表水与井水混合在一起，然后才输送给客户以降低饮用水中 铀的浓度。自 1990 年代以来，里贾纳市的饮用水几乎 100％来自地表水。水质监测数据表 明，水中的铀浓度随着引入水系统的地表水数量的增加而呈指数下降。来自加拿大放射监测 网络数据库的历史数据显示，铀的年平均浓度从 1980年的 12.3μg/L降至 2016年的 0.5μg/L。 经 Chen 等人许可改编（2017）。加拿大饮用水中的天然放射性核素综述（1975-2016）， 《辐射防护剂量法》，第 1-11 页，包含根据开放政府许可证 v3.0 许可的公共部门信息。 总 铀 年 平 均 浓 度 ， g/ L 23 1.6 饮用水中的氡 1.6.1 氡如何进入饮用水？ 氡是镭同位素的衰变产物（天然铀和钍衰变时产生）并且存在于地下。氡是 一种惰性气体，易溶于水，所以水流经地下很容易溶解氡并输送较远的距离。在 饮用水供水中含量最大的是最长寿命的氡-222，其半衰期为 3.8 天。部分过程氡 可以从水中逸出，比如水处理、储存和传送的过程通常可以降低氡的浓度。但是 来自于天然泉、钻孔或井的饮用水，水提取的过程较短，直接使用很可能导致增 加氡的照射。地表水中氡的水平通常很低因为其很容易释放出来到大气中。 1.6.2 是否需要建立饮用水中氡的国家标准？ 不需要。GDWQ 未规定氡的指导水平，因为考虑测量室内空气中的氡浓度 比测量饮用水中的氡浓度更合理。国际上的综述研究数据（UNSCEAR，2000） 得出结论，饮用水中可归因于氡的剂量平均有 90％来自吸入而非食入。当水被 加热或搅动（例如沸腾、淋浴、沐浴和厕所冲水）时，溶于饮用水的氡可以释放 到空气中。但是，室内空气中氡的主要来源可能来自建筑物中的岩石和土壤，而 不是饮用水。WHO 建议的室内空气国家参考水平为 100 Bq/m3（WHO，2009）。 如果在当前的特定国家/地区条件下无法达到该水平，WHO 氡手册指出的参考水 平不应超过 300 Bq/m3。从水中释放到室内空气的氡的照射研究(Hess et al., 1987; Nazaroff et al., 1987)中估计的总转移系数为 10-4，用此转换系数，对于自来水中 1000Bq/L 氡的活度浓度增加室内空气中的氡浓度大约为 10Bq/ m3。 如果要制定饮用水中氡的国家标准，则饮用水中氡的筛查水平应基于室内空 气中氡的国家参考水平。一些国家已制定了饮用水中氡的国家标准（见信息栏 1.21）。 信息 1.21：欧盟饮用水水质指令中设定的饮用水中氡的国家标准 《欧盟饮用水水质指令》（EC, 2013）为饮用水中的氡设定了 100 Bq/L 参数值。成员 国可以设定一个氡的水平，在不影响供水时作为国家或区域判定其高于或低于防护最优化的 标准。成员国设定的氡水平可能高于 100 Bq/L，但必须低于 1000 Bq/L。此外，如果氡浓度 超过 1000 Bq/L，出于辐射防护的理由，无需其它考虑即可采取补救措施（EC, 2013）。 1.6.3 应在供水链中哪一点开展饮用水中氡的测量？ 理想情况下应在饮用时取样。这是因为处理过程会导致水的搅动而使氡从水 中以气体释放，或者配送和储存过程导致氡的衰变，致使从水源到饮用时水中氡 的水平可以降至很低。因此，在水源处对氡进行测量可能无法反映所饮用的水中 氡的浓度，而且值可能很高。然而，在地下水源处测量氡有助于确定饮用水中存 在氡的可能性，并为可能需要采取的任何补救措施提供决策依据。 1.6.4 哪些方法可以应用于饮用水供应中氡的采样和测量？ 饮用水中氡的正确采样和随后测量的准确性主要取决于处理过程中是否从 样品中损失了氡气体。在野外采集水样和在实验室中处理水样品时，需要格外小 心，以防止氡损失。因此需要训练有素的工作人员。 24 样品收集在不透氡材料制成的容器中，例如铝或玻璃。将水以非常低的流速 缓慢倒入容器中，以避免氡从样品中曝气或脱气。将水样品转移到卢卡斯闪烁室 （用于检测氡的闪烁室），以确保运输到实验室不会导致样品中氡的损失。由于 采集和处理过程可能损失氡，建议在采集时采集多个样本。 测量饮用水中氡的两种主要实验方法是广泛应用的液体闪烁计法和伽玛谱 法（见 3.5）。由于氡的半衰期短，理想情况下应在样品到达实验室的当天进行 分析。 重要提示，由于氡的易挥发性，水中总 α 的筛查测量中不包括氡。 关于饮用水中氡测量方法的更多信息，见 WHO 室内氡手册的 2.1.3 节（WHO， 2009）。 1.6.5 水源中氡浓度高时如何管理饮用水中的氡？ 在已经确定或怀疑地下水中氡浓度较高的情况下，需要考虑吸入和食入照射 两方面，以判定是否需要采取降氡步骤。与吸入相比，饮用水中氡的食入照射较 小，控制总体照射的重点很可能是降低氡从地面进入室内空气中的氡浓度。一栋 建筑的室内空气中氡含量很高，单独是由于供水所致的情况不常见。 对于经过处理的集中式供水，去除高浓度氡最有效的处理方法通常是对水进 行曝气，这可以去除高达 100％的氡。如果水处理厂有屋顶，会导致每天从事维 护工作人员在这里的空气中氡的累积。对于空气中氡的积累，首先应对空气中的 氡进行测量以确定工作环境中的水平。这种情况下有两种方法可控制氡的照射： 进行建筑物通风或向室外抽风；在不可能做到这一点的地方，控制高氡环境中工 作人员受照射的时间。 进入家中的水通过处理也可以降低饮用水中氡的活度浓度。最有效的处理方 法是对水进行曝气，它可以去除高达 100%的氡，但水中的氡释放到空气中然后 排放到户外非常重要。也可以使用带或不带离子交换的粒状活性炭过滤，这比曝 气便宜，但其降氡含量的效果较差（例如，Annammaki & Turtianen，2000）。 在同一供水系统为多个住宅提供服务的情况下，在为多个住宅供水的管网的 某个点而不是在单个物业区，去除氡可能更实用且更具成本效益。 如果采取补救措施来管理室内空气中的氡水平，这些措施也将起到降低饮用 水所致空气中氡浓度的作用。但是，如果供水来自附近的地下水源，则建议持续 测量饮用水中的氡。 25 2 应急情况 2.1管理饮用水水质的应急情况和标准的背景 2.1.1什么是放射应急情况？ 由于事故、恶意行为或任何其他不可预期的事件，需要立即采取措施以避免 或减少不利后果，从而导致出现放射应急情况。一旦发生应急情况，可以通过采 取防护措施来减少辐射照射。 2.1.2核或放射事故应急后，饮用水中的放射性核素是否可能存在长期的公众健 康风险？ 不可能。在发生核或放射事故应急后，饮用水中的放射性核素极不可能导致 长期公众健康风险。尽管在涉及释放到大气或水源的核或放射应急情况（见 2.3.2） 后，开放式地表水源最容易受到污染，但由于大量水的混合，饮用水中的放射性 浓度将迅速降低。应该注意的是，如果应急情况下放射性核素在大气中最初沉积 在积雪或冰上，这可能导致地表水源的饮用水所致的剂量将延迟到雪/冰融化。 然而，对于早期任何污染了的地表水，通过大量水的混合，此类水源的饮用水中 放射性核素的活度浓度也将很快被显著稀释。信息栏 2.1 讨论了福岛第一核电站 事故后实施的饮用水限制条件。 放射性核素释放到环境中不会造成地下水源的直接污染；这些饮用水源不会 受到任何重大污染（见 2.3.2）。 饮用水供水的蓄意污染（即恶意行为）可能涉及地表水和地下水源、或直接 进入供水，该情况下饮用水中的放射性核素仅在很短时间内存在高活度浓度，因 此饮用水中的放射性核素极不可能存在长期的健康风险。 信息栏 2.1：日本发生事故后对饮用水实施限制的示例 日本福岛第一核电站事故发生后，对服务于总人口约 1400 万的 20 家自来水公司的取水 量进行了限制，最长的限制是 12 天，除一个地区（人口约 4000）外，那里的婴儿摄入限制 持续了 51 天（更多信息见 4.5）。 2.1.3应急情况何时结束且这对饮用水水质有何考虑？ 从应急情况到非应急情况（现存照射）的过渡以及应急情况的后续终止将由 主管当局根据当前的情况在满足标准或预案中的相关标准后做出决定（ ICRP, 2009；IAEA, 2015；IAEA, 2018）。在过渡期内，采纳应急情况下的饮用水标准（IAEA, 2015；2011）。一旦有关当局宣布结束应急情况，应急情况下所造成的任何残留 在饮用水及其水源中的放射性核素应将视为非应急情况（在非应急情况下,饮用 水标准 GDWQ 适用，见 1.3.1）。核或放射应急准备和响应的国际安全标准丛书 （IAEA，2011）指出，事故的应急阶段结束后，应尽快使用 WHO 的 GDWQ，以 确定饮用水是否适合长期饮用。 2.1.4是否有适用于应急情况下饮用水水质的国际标准和准则？ 有。IAEA 有关于核与放射事故应急情况下的准备与响应安全标准丛书，其 包括通用安全要求（GSR）第 7 部分（IAEA, 2015）和通用安全指南（GSG）2 号： 核或放射事故应急准备与响应准则（IAEA, 2011），这些适用于应急情况饮用水 的标准。这些标准由包括 WHO 在内的许多国际组织共同制定。 26 根据这些国际标准，政府有责任在准备阶段确保防护策略的先进性、正当性 和最优化，以便在核或放射应急情况下采取有效的应急措施。防护策略将包括采 取应急行动（包括饮用水行动）的标准。 分别在 GSR-7 和 GSG-2（IAEA, 2011; 2015）中包含了用于规划目的的预测辐 射剂量通用标准和应急情况下的操作干预水平（OIL），这将保证采取应急保护 措施，例如禁用饮用水。 GSR-7 提供了预设剂量的通用标准，有关饮用水消耗的限制，通常必须 按此标准实施。这些通用标准可应用于根据可直接测量的量制定操作层 面的标准以在应急情况下加以相关限制。 GSG-2 根据总 α和总 β活度浓度（即 OIL5）以及饮用水中大量放射性核 素的活度浓度（OIL6）提供了默认 OIL，以在应急情况下施加相关限制 饮用水的消耗。 筛查标准（OIL5）为： OIL5 –总 α：5 Bq/kg OIL5 –总 β：100 Bq/kg 饮用水的 OIL5 和 OIL6 值是基于应急情况发生后第一年通用剂量标准 10 mSv 导出，假设未采取任何防护措施、所有饮用水全年均受到 OIL 活度浓度的污染并 采用最限制性的年龄组和消费量。因此 OIL 值为保守值，因为发生核或放射事故 后饮用水中的活度浓度将在最初的污染后迅速降低并且全年不会保持恒定水平。 10 mSv 是第一年在应急情况下实施早期防护措施和其他响应措施的通用标准 100 mSv 的 10％（IAEA，2015）。使用 10 mSv 可确保来自所有照射途径的剂量 不会超过标准 100 mSv。2.3.1 和 2.4.1 提供更多有关 OILs 的信息及其用法。 基于上述国际标准，各国家可以考虑国际标准所提供的准则，同样考虑当地 的环境情况（例如环境、人口、社会、政治，经济以及其他因素）制定自己的国 家标准。考虑所有这些因素旨在确保国家标准指导合理性、最优化的应急响应行 动。 任何长期持续的饮用水限制条件，最终目的可能都是达到一个参考水平（或 国家标准），考虑 WHO 的个人剂量标准（ 0.1 mSv/a）和国际基本安 全标准（BSS）中的参考水平（1 mSv/a），从而平衡、优化技术、经济、环境以 及社会环境情况。 2.2发生核或放射应急情况时饮用水的健康风险 2.2.1在核或放射应急情况下饮用水中可能涉及哪些放射性核素？ 核或放射应急情况下饮用水中可能涉及的放射性核素取决于应急的类型、所 涉及的设施与运行的类型（例如，核电厂事故，使用放射性核素的工业医疗事故 性排放或交通事故）以及其进入饮用水源和供水的能力（Brown，Watson 和 Nisbet， 2015；WHO，2017a）。 表 2.1列出了与核或放射事故应急情况下饮用水可能涉及照射的相关放射性 核素，包括事故情况和所致地表水污染的途径。尽管工业用放射源引起的放射性 事故较常见（UNSCEAR，2016），但其极不可能引起饮用水的污染，因此，针对 此类事故的放射性核素未包括在表中。信息栏 2.2 提供了一个事故后最关键的放 射性核素采样和测量的示例。 27 信息 2.2：事故后识别重要放射性核素的示例 在日本福岛第一核电站事故中，识别具体放射性核素显示，事故发生后铯-134，铯-137 和碘-131 在饮用水中浓度极高。测得的其他放射性核素（包括锶和氚）的放射性浓度要低 得多。来源: WHO (2012)。 表 2.1 核或放射应急情况下饮用水可能涉及的放射性核素 核素 使用/产生的突发事件场景 地表水污染的途径a 3H 核反应堆运行产生 释放到大气 直接污染水 60Co 核反应堆运行产生 释放到大气 直接污染水 90Sr / 90Y 核反应堆运行产生 释放到大气 直接污染水 95Zr / 95Nb 核反应堆运行产生 释放到大气 99Mo / 99mTc 医疗(核医学锝发射器) 核反应堆运行产生 释放到大气 直接污染水 103Ru 106Ru 核反应堆运行产生 释放到大气 132Te 核反应堆运行产生 释放到大气 131I 医疗(用于诊断/治疗程序的核医疗设施) 核反应堆运行产生 释放到大气 直接污染水 134Cs 136Cs 137Cs / 137 m Ba 核反应堆运行产生 释放到大气 直接污染水 140Ba / 140La 核反应堆运行产生 释放到大气 144Ce 核反应堆运行产生 释放到大气 235U 反应堆和核武器 直接污染水 238Pu 239Pu 核反应堆运行产生 核武器(239Pu) 释放到大气 直接污染水 241Am 医学诊断 核反应堆运行产生 释放到大气 直接污染水 如果放射性衰变子体是健康风险的主要贡献者，已隐含在列表中。 释放到大气中会导致沉积在水源和处理过的水上，或通过集中供水间接进入水源。 2.2.2在核或放射应急情况下，建立饮水标准时是否儿童需要更严格的防护？ 对于应急情况，国际标准（IAEA，2015；2011）中确定的标准考虑了最容易 受到辐射照射的公众（即儿童和孕妇）。这些标准由年龄限制最大的剂量转换因 子和摄食率（即婴儿的摄食率）导出，以确保最易受影响的人群免受相对较高的 短期剂量。这些假设所导出的可操作性的标准是保守的。 一些国家可能针对不同年龄组对特定的放射性核素制定不同活度浓度的标 准（见信息栏 2.3）。这种方法可能会给针对不同人群要采取不同行动带来挑战， 也难以向公众传达明确的信息，为什么某些家庭成员可以消费饮用水而其他人则 不能饮用。 28 信息 2.3：为儿童设置不同标准的示例 福岛第一核电站事故发生后，日本根据最易受影响的年龄组，设定了饮用水暂行条列， 其中放射性铯（137Cs 和 134Cs）的值对于成人、幼儿和婴儿相同（300 Bq/kg）（Iwaoka， 2016）。但是对于碘-131，根据婴儿对甲状腺的不良反应比其他年龄组高，饮用水标准设置 成人和儿童的为 300 Bq/kg、婴儿和用于制作瓶装奶的水较低（100 Bq/kg）（CODEX, 2001）。 2.2.3在核或放射应急情况下，与其他照射途径相比饮用水中放射性核素所致的 健康风险如何？ 如 2.1.2 所述，在发生核或放射应急情况下，饮用水中的放射性核素极不可 能长期存在公众健康的风险，除蓄意污染供水系统。在应急情况下，居住在事故 现场附近的公众受到的主要剂量贡献来自于地面上放射性核素的外照射和吸入 空气中放射性核素的内照射。随着距离事故现场的距离越来越远，摄入食物、牛 奶和饮用水中的放射性核素导致的内照射占主导地位，但远低于事故现场附近的 人员所受到的剂量。 根据释放到环境中的放射性核素，长期的剂量贡献主要是外照射和/或食入 食品而非饮用水。这是在福岛第一核电站事故后所观察到（WHO，2012；2013）， 见信息栏 2.4 的描述。 信息 2.4：一事故后重要照射途径的示例 2011 年 3 月 11 日日本福岛第一核电站事故后，日本当局测量了饮用水中放射性核素的 水平。第一批饮用水样本于 2011 年 3 月 16 日在福岛县采集。在事故发生后的几个月里，水 平仅在有限的时间内升高。在福岛县内，估计了 2011 年 3 月至 2012 年 3 月期间每个地区 居民的剂量，例如，在饭馆村，饮用水中放射性核素对 1 岁儿童的辐射剂量估计低于所有外 照射和内照射（包括食物摄入）总剂量贡献的 5％。 2.3在应急情况下测量饮用水中的放射性核素 2.3.1在核或放射应急情况下哪些筛查方法用于测量饮用水中的放射性核素？ 测量饮用水中总 α和总 β活度浓度用于饮用水的常规监测，也可以应用于核 或放射应急情况。然而这些筛查技术无法识别存在的放射性核素具体种类及其活 度浓度。使用筛查方法的一个优点是这些国家的水监管部门内部和实验室可能已 经具备了这种能力，而用于测量具体放射性核素的设备也许没有可供使用的（见 3.5）。在许多情况下，总 α 和总 β 筛查方法可用于证明活度浓度低于为应急情 况设定的操作干预水平（OIL），从而节省了放射性核素分析所需的时间和资源。 IAEA 安全指南 GSG-2 中关于总 α和总 β活度浓度的 OIL（OIL5）旨在用作核 或放射应急情况的筛查标准（IAEA，2011）（见 2.1.4 和 2.4.1）。OIL5 值与非应 急情况下的总 α和总 β筛查水平不同（见 1.3.3）。 尽管筛查方法在大多数情况下可适用，但根据所使用的测量技术，总 α或总 β 不能测量到某些放射性核素（例如氚，硒-75，铌-95，钌-103 或镱-169），因 此总放射性测量中不包括这些核素。某些气态或挥发性放射性核素（如碘的同位 素）也不包括在检测中，因为在分析过程中放射性核素会损失。如果怀疑这些放 射性核素在应急情况下已经释放并且可能存在于饮用水中，则还必须开展特定的 放射性核素检测。 29 如果已知应急情况下释放的放射性核素，特别是在小规模应急或仅涉及有限 需要检测的供水情况下，在初期测量单独的放射性核素可能最有效，并且直接与 特定的放射性核素标准（例如 OIL6 值）进行比较。 各国可以根据本国的应急标准设置相应的饮用水筛查水平（见 2.1.4）。信 息栏 2.5 中提供了设置筛查水平的示例。 信息 2.5：设置应急情况筛查水平的示例 英国环境署制定了总 α 和总 β 筛查方法监测饮用水的指南。根据总活度浓度制定的应 急筛查水平（见下文），应用于辐射事故发生时检测是否需要采取干预措施来降低饮用水中 的活度浓度。 英国饮用水中总总活度浓度的应急筛查水平 监测类型 应急筛查水平 总α放射性 5 总放射性 30 （对比，非应急情况下总α的筛查水平为0.1 Bq/L 和总β的筛查水平为1 Bq/L。） 来源：Brown, Watson & Nisbet, 2015. 2.3.2核或放射应急期间可能会影响哪种类型的水源？ 在涉及放射性核素释放到大气或水源的核或放射性应急情况发生后，河流和 水库等水源可能最容易受到放射性核素污染。在这种情况下，除了直接沉积到地 表水源之外，从周围土地流失以及被放射性核素污染的积雪或冰的融化也可以长 期进入地表水中，会影响水库或输送水，这不包括故意用放射性核素污染供水系 统（例如恶意行为）。 直接污染不会立即对地下蓄水层产生影响，从长远来看，如果放射性核素从 土壤和岩石向下渗透，有可能会污染到这些水源。放射性核素的侵入也可能通过 保护不良的井和钻孔发生，特别是事故相关联的洪水。 如果在顶部有烟囱时发生降雨，在住宅内的饮用水水箱和蓄水池中收集的雨 水可能含有放射性核素，由于在烟羽经过之后，放射性核素会随着进一步降雨而 迅速稀释，因此饮用这些水的时间很短，而且这种水的饮用将受到储存罐大小的 限制。国际安全标准（GSR-7）（IAEA，2015）建议考虑在核设施周围采取预防 措施，以保护使用雨水或其他未经处理的地表水的饮用水供应免受直接污染，作 为应急计划的一部分。。 2.3.3在核或放射应急期间重点监测哪些水源？ 随着放射性核素释放到大气，首先要重点监测受放射性烟羽影响的地表水的 供水源，这些水源很可能含有最高水平的放射性核素，而且事故后很快被污染。 水中的放射性核素水平取决于从事故发生处到下游水流经过的距离，因为大气扩 散的距离和水的稀释，放射性核素的水平会随着距离的增加而降低。 地表水集水区的径流可能是饮用水供应中的长期放射性核素来源，并且根据 集水区的性质和排放量的大小，可能会影响最初受到放射性羽流污染的水源之外 的其他水源。放射性核素的水平不太可能引起公众健康问题（见 2.1.2），但是 应该对处理厂或储存的供水进行监测，以证明活度浓度较低。 30 在最初放射性核素在大气中沉积或在积雪上/冰上沉降的地区，监测计划需 要考虑到地表水的任何初始污染以及积雪解冻后可能发生的地表水污染，如 2.1.2 所述。这可能需要根据融化速率以及随后放射性核素从冰/雪包顶部释放到 地表水中的释放速率进行长时间监控。 重要的是进行测量的水样代表所消耗的饮用水，以便与执行标准比较（例如： 操作干预水平（OIL））。如果在消费前对水进行了处理，则应在处理后对水进 行监测，因为处理会降低水中许多放射性核素的活度浓度（见 3.2）。 饮用水的长期监测计划应包括监测地下供水，以确保这些水源中的放射性活 度浓度保持低水平。 2.4应急情况下超出饮用水标准的管理 2.4.1在核或放射应急时如何使用饮用水的操作干预水平？ 饮用水测量结果，如果未超过为应急情况建立的总 α或总 β筛查标准（操作 干预水平（OILs），比如 OIL5 值），所有公众包括婴儿、儿童和孕妇在内均可饮 用此水。 如果超过筛查标准的任一指标，则在确定是否应限制饮用水饮用之前，需要 测量具体放射性核素的活度浓度。如果总超过筛查标准（OIL5），先要通过总 钾的测量扣除钾-40 的贡献。 这种分阶段的方法（如图 2.1 所示）与 GDWQ 中针对非应急情况使用筛查水 平和指导水平值的建议相一致。 关于核或放射应急情况的准备与响应使用标准的通用安全指南GSG-2（IAEA， 2011）提供了 300 多种放射性核素的活度浓度（OIL6）值。OIL6 值非常保守，因 为它们是根据假设饮用水中的活度浓度全年都保持在这一水平推算出来，这极不 可能是应急发生后的情况（见 2.1.4）。如果任一放射性核素的活度浓度超过 OIL6 值，则可能不适合饮用，必须考虑采取降低饮用水中放射性活度浓度的措施，以 及减少饮水的剂量（见 2.4.2）。然而，OIL6 值的确定是基于公众中最易受伤害 的人群（例如婴儿和孕妇），并且假定所有饮水都被污染了一整年，因此超过标 准并不一定意味着饮用水不适合饮用。需要进行进一步的调查，包括考虑实际的 消费率和进一步的测量（更多信息，见 2.4.2）。 重要的是在应急情况下尽快了解饮用水中存在的放射性核素。预期可以在大 约一周内对饮用水供应进行 OIL5 和 OIL6 值筛查，以确认在应急情况发生后立即 对饮用水的消费采取任何预防性限制（IAEA，2011）。 31 图 2.1 在应急情况下应用 OIL 的分阶段方法 2.4.2 如果超过应急情况下的饮用水标准，需要采取什么行动？对于小型供水， 包括社区供水，是否要采取特殊行动？ 如果在核或放射事故后饮用水的供水受到放射性核素污染，则部分被污染的 水很可能被饮用。如 2.1.2 所述，饮用水中的放射性核素不太可能带给公众长期 的健康风险，放射性核素仅在很短的时间内存在相对较高的活度浓度。因此，有 效地传达饮用这种饮用水有关的风险非常重要，无论是在饮用水中所含放射性的 浓度低于操作干预水平（OILs）还是在有限的时间段内高于这些水平（见 2.4.1）。 如果超出 OILs，则国际标准建议对非必要饮用水的消费实施限制是一项保护 措施（IAEA，2015；2011）。如果因为限制了所供饮用水无法避免导致缺水且无 法获得替代水时，可以饮用此水直到有替代水可用。但是即使消耗了该饮用水， 也不可能像 2.1.4 中所讨论的那样造成重大的健康风险。虽然对健康的放射风险 可能会略有增加，但是不会像没有饮用水供应所致的健康危害风险那么大。如果 有放射性碘的污染，则建议实施碘甲状腺阻断的国际标准（WHO，2017b）。参 考关于碘甲状腺阻断实施的标准相关信息（IAEA，2011；WHO，2017b）。 对于应急情况下饮用水超出了预先建立的标准，可以考虑采用不同的水管理 和补救措施，下面将简要说明这些措施。所选择的措施将取决于具体情况，选择 措施时要考虑的因素包括超出应急标准的程度，措施的成本以及其他供水的可用 率。此处提供的信息具有一般性，需要根据国家背景和资源对特定情况的选择措 超过 OIL5？ 测量具体放射性 核素活度浓度 超过 OIL6？ 可以饮用 除特殊情况外 不可饮用 否 否 是 是 32 施进行全面评估。有关合理措施的更多详细信息，见辐射事故后的恢复手册，例 如，英国 2015 年辐射事故的恢复手册-饮用水供水手册（Brown, Watson & Nisbet， 2015）。 通过详细监测计划的支撑，继续使用饮用水供水。如果放射性核素的半衰期 小于约一周，则由于超标的时间短，依靠常规的水处理、监测以及与公众良 好的风险沟通，可能没有必要考虑采取任何具体措施来降低饮用水中的活度 浓度。可能这是最可行的措施，尤其对于小型社区供水。 提供不含放射性核素的替代饮用水，例如瓶装水或罐车装载的未受污染区域 的水。供水中的水仍可用于卫生目的。作为应急响应计划的一部分，自来水 公司应制定提供和分配应急供水的计划。重要的是要确保替代供应不会带来 额外的更大的风险。 将水源更改为不含有高于标准的放射性核素的水源（更改取水点或水源位 置）。未受到事故影响或所受影响较小的水源可以供用。也可以从地表水源 更换到地下水源。应特别注意，确保水源的变化不会导致无法控制或难以控 制的其他更大风险的引入（例如，地表水源常会被污染，尤其是受到微生物 污染）。 控制供水的混合。如果在水处理或后期处理时有多种供水，则所关注的饮用 水可以与未受到事故影响或所受影响较小且放射性核素活度浓度较低的水 混合。这是降低饮用水中活度浓度的有效方法，并且具有不产生放射性废物 的额外好处。对于小型私人或社区供水混合方式可能不实用。 进行水处理或对现有水处理进行更改。结合絮凝、沉淀和砂滤工艺处理地表 水的水处理厂，可能会去除源水中存在的 30％至 100％的放射性核素，具体 取决于放射性核素。有关常见放射性核素在水处理过程中去除性能的更多信 息，见 3.2。美国环境保护局（2005）第 I 部分给出了一个通用清单的示例， 其帮助确定实施额外水处理是否为最合适可行的选择。实施新的水处理或对 现有水处理进行重大更改是一项重大工程，而且不太可能很快实施。 ― 水处理措施通常会产生废物，其中将包含从水中去除的放射性核素（见 3.3）。 ― 商用的处理设备可用于家庭或私人场所以减少饮用水的放射性污染。包 括用于软化水的水过滤系统，该系统使用带有某些离子交换材料的碳过滤器 （水罐过滤器）和小型反渗透装置。这些产品应获得相关标准组织的认证。 家用水处理设备将产生废物，其中将包含从水中去除的放射性核素（见 3.3）。 这些更可能适用于小型社区或仅小型供水受到影响的社区，因为它们无法大 规模使用，因此需要对其使用进行仔细控制，以确保其有效性并适当处理废 物过滤器。信息栏 2.6 和信息栏 2.7 讨论了针对 2011 年福岛第一核电站事故 采取的补救措施。 信息栏 2.6：遮盖露天蓄水池 在放射性核素释放到大气的过程中，放射性核素可能直接沉积到取水点的水源水中、正 在处理或输送前已处理了的水中。在这种情况下，如果在释放前或释放后立即采取措施保护 供水系统，例如遮盖开放式储水池，以保护其免受干湿沉积的直接污染，可能是有效的。例 如福岛第一核电站事故发生后，日本覆盖了水处理池。 33 信息栏 2.7：事故发生后限制饮用水的饮水量 在 2011 年 3 月 11 日日本福岛第一核电站事故中，五个县的 20 个自来水公司实施限制 婴儿饮用自来水的摄入量，因为放射性碘超过了婴儿的限值（100 Bq/kg）。除福岛县以外， 其他大部分禁区都持续了两到三天。到 2011年 5月 10日，所有婴儿的摄入量限制都被取消。 所有年龄组的摄入量限制仅在 2011 年 3 月 21 日在福岛县的一家小型供水公司实施；这是因 为放射性碘的水平超过了 300 Bq/kg（成人的指标值）。该限制于 2011 年 4 月 1 日解除。在 限制期间，分发了瓶装水或罐车装水，更多信息见 4.5 部分。 34 3 支持信息 3.1煮沸的水会减少饮用水中放射性核素的照射吗？ 不会。沸腾不会降低饮用水中放射性核素的浓度。但是，由于沸腾减少水量， 过度（即连续或长时间）沸腾可能会导致更高浓度的放射性核素（见信息栏 3.1）。 信息 3.1：通过饮用水煮沸降低活度浓度 福岛第一核电站事故（Tagami＆Uchida，2011 年）之后在日本开展的测试表明，自来水 无论短期煮沸（1-10 分钟）还是长时间沸腾（达 30 分钟）都不会减少碘-131。长期的沸腾 致使碘-131 的浓度增加，因为体积减少了三倍。 3.2从饮用水中去除放射性核素的水处理方法有何效果？ 地表水通常比地下水接受更多的处理，特别是浊度高（大量悬浮颗粒物）和 微生物含量高的水源（见表 3.1）。经过更广泛处理的水的放射性核素去除率可 能更高。对于处理较少的水源（例如许多地下水源），去除的污染物（包括放射 性核素）就较少。 表 3.1 地表水和地下水特征 特征 地表水 地下水 浊度 高 低 溶解的矿物质 低-中 高 微生物含量 高 低 时间变异性 很高 低 通常将凝结与沉淀或过滤相结合进行处理，在某种程度上能有效地去除悬浮 的放射性核素，对于主要的天然放射性核素其有效性范围约 30％至 100％，通常 约为 70％（见表 3.2）。离子交换过滤器（最常用于地下水）能有效去除镭和铀， 可去除 70％以上。然而通常安装这些装置是为了去除水中的硝酸盐，并且可能 会在优先性方面与放射性核素竞争。信息栏 3.2 提供了福岛第一核电站事故后过 滤措施的示例。 下表改编自 GDWQ 第 9 章中的表 9.4，汇总了一些常见水处理过程中对某些 元素的去除性能。有关更多详细信息，可以在 Brown，Hammond＆Wilkins（2008b） 和 USEPA（2005）中找到有关不同水处理过程有效性的综述，以及介绍可能影响 水处理过程的因素。GDWQ 附件 6 中还提供了放射性核素特定处理技术的参考。 关于去除铀、镭、铅和钋的技术及其有效性的更多信息，也可以在 Annanmaki ＆Turtianen（2000）中找到。应该注意，去除性能将非常具体地取决于水源和所 进行的处理，所提供的信息仅表明预期浓度的降低。 35 表 3.2 水处理性能 元素 凝结 砂过滤 活性碳 石灰-苏打软化 离子交换 反渗透 锶 XX XX X XXXX XXX XXXX 碘 XX XX XXX X XXX XXXX 铯 XX XX X XX XXX XXXX 镭 XX XXX XX XXXX XXXX XXXX 铀 XXXX X XX XXXX XXXX XXXX 钚 XXXX XX XXX X XXXX XXXX 镅 XXXX XX XXX X XXXX XXXX 氚 不可能去除 符号说明：X：去除0–10%；XX：去除10–40%；XXX：去除 40–70%；XXXX：去除> 70% 来源：改编自 WHO (2017a)中第九章的表 9.4 信息栏 3.2：水处理去除碘-131（131I）、铯-134（134Cs）和铯-137（137Cs）的有效性 福岛第一核电站事故发生后，对一些水处理厂进行了测量，以研究在水处理过程中去除 碘-131 和放射性铯（铯-134 和铯-137）的有效性。 碘-131 在两个水处理厂中，发现凝结和沉淀未去除碘-131（原水浓度 5.7Bq/L，发现处理水浓 度为 2.9 Bq/L、2.8 Bq/L 和 5.4 Bq/L）（Kosaka et al., 2012; 2014）。这种情况，认为原水中的 碘-131 以可溶性存在而不是颗粒悬浮粒子。 发现粒状活性炭工艺确实除去了碘-131，水处理厂中从 2.8 Bq/L 降至 1.9Bq/L，即去除 了 34％，粉末状活性炭处理也能有效去除碘-131。目前水处理厂中，粒状活性炭和粉末状 活性炭对碘-131 的去除率约为 30％至 40％。小型去除试验中，每升河水（碘-131 约 3.5 Bq/L） 分别用 10、25 和 50 mg 粉末状活性炭处理 30 分钟，分别去除了 9％，36％和 71％。在粉 状活性炭处理之前，以约 0.5至 1.0 mg/L的弱预氯化处理，使用上述相同的粉状活性炭实验， 可将去除率提高至 41％，59％，71％。 放射性铯（134Cs 和 137Cs） 研究发现，如果水处理厂中的放射性铯主要以颗粒形式存在，它会选择性地吸附在某些 类型的土壤颗粒上或内部，然后通过颗粒分离过程（包括凝结和絮凝、沉淀和砂滤）将其除 去。福岛第一核电站事故发生约 1.5 个月后，检测了水处理厂中 134Cs 和 137Cs 的去除情况， 原水中 134Cs 和 137Cs 的水平分别为 5.6 和 6.4 Bq/L，而经混凝和沉淀后的水平低于探测下限 （分别为 0.50 和 0.83 Bq/L）。这些结果表明，放射性铯悬浮颗粒的浓度降低了 10 倍。在使 用河水的小型混凝试验中，134Cs 和 137Cs 的浓度分别为 5.6 和 6.4 Bq/L，浊度为 51 度（大约 35-41 浊度单位），134Cs 和 137Cs 的去除率分别为 94％和 95％，证实了悬浮颗粒形式的去除 率很高。 相比之下，以溶解离子形式存在的放射性铯则无法去除。在事故发生约 1.5 年后的 2012 年 10 月，对两个水处理厂通过凝结、沉降和砂滤去除离子态的 134Cs 和 137Cs 进行测量，两 个原水中溶解离子态的 134Cs 和 137Cs 水平分别为 0.005 和 0.010 Bq/L，处理后的水中的 134Cs 和 137Cs 水平分别为 0.005 和 0.011 Bq/L（Ohno 等人，2013）。在实验室规模的试验中，使 用了反应堆场址污水池水，进一步观察证明了传统的凝结和砂滤工艺不能有效去除离子态的 放射性铯。池水中的 134Cs 和 137Cs 分别为 9.8 和 11.0 Bq/L，浊度为 0.3 度（约 0.2-0.3 NTU）， 通过该凝结试验除去 134Cs 和 137Cs 分别仅为 5％和 6％（Kosaka et al., 2012）。 36 这些结果表明，颗粒分离过程在去除放射性铯的颗粒态方面非常有效，但它们并没有去 除溶解离子形式的放射性铯。 作为去除溶解的放射性铯离子的潜在有效方法，建议添加土壤颗粒。在实验室规模的测 试中，向脱氯的自来水中添加 200 mg/L 直径为 25-75μm 筛分的部分土壤（添加了 0.1μg/L 的 133Cs）并搅拌 30 分钟，使用这种方法，最初溶解形式的 133Cs 中的 50％被去除（Tampo 等人，2016）。 3.3如果通过处理去除了饮用水中的放射性核素，水处理过程的废物 是否需要作为放射性废物处理，将终止于何处？ 如果在处理过程中从水中除去放射性核素，它们将最终进入处理过程产生的 废物中。对于传统的絮凝、沉淀和过滤过程，主要废物是污泥（来自絮凝）和过 滤介质（例如沙子）。 絮凝过程中产生的污泥是一种浓缩方法，通常所产生的污泥量与被处理大通 量的水相比很小。污泥的量取决于水源水的质量及其浊度，浊度越高，处理产生 的污泥就越多。过滤器的反冲洗也会产生污泥。例如，在一项对澳大利亚昆士兰 州东南部生活用水处理产生的放射性残留废物的研究中，每百万升处理过的地表 水产生的污泥范围为 0-46千克，平均每百万升水 14千克（Kleinschmidt ＆Akber， 2008）。作者指出，这与其他国家的报告一致，并给出了与德国和美国的比较值。 对于具有高通量水的处理厂，将产生相对较多的污泥。信息栏 3.3 给出了在非应 急情况下对污泥进行测量的示例。 放射性核素在沙子和活性炭等滤床中的积累也是一种浓缩方法，水流经滤床 时将放射性核素积聚，并且随着时间的推移，滤料上的单位活度浓度会增加。补 充滤床介质的次数越少，浓度就会越高。通过过滤去除的放射性核素与过滤材料 有关，并且单位质量过滤材料中放射性核素的活度浓度可能会低于废物污泥中的 放射性浓度，更多信息见 Brown, Hammond＆Wilkins（2008a）。 离子交换和反渗透也能使放射性核素积聚在交换树脂或反渗透膜上。尽管这 些可以通过再生去除，但这种再生将导致放射性核素排放到废水中，这可能需要 加以控制。 在去除过滤介质和过滤器或更换离子交换膜或反渗透膜时，需要予以考虑包 括在恢复水处理之前对其进行去除、运输、更换和再生等实际情况。 水处理产生的废物中不太可能但仍可能被要求考虑作为放射性废物进行管 理。在应急情况发生后，短期内废物（尤其是污泥）中的活度浓度可能很高（如 信息栏 3.4 中所示），如果发生核或放射应急情况，则应考虑对处理后的废物进 行测量以防放射性核素进入水源。需要听取相关监管部门的专家建议。在 USEPA （2005）中可以找到有关饮用水处理中放射性废物管理的一些背景信息。 尽管在处理废物材料中非常不可能对水处理过程中工作的人员造成任何照 射和任何显著的健康风险，但应该考虑并可能需要控制从事水处理的作业人员的 潜在健康风险，3.4 中将提供更多信息。 37 信息栏 3.3：澳大利亚非应急情况下污泥中活度浓度示例 在澳大利亚北部地区一现场，从钻井中抽取的地下水，在储水池中储存沉淀，然后再配 送（Kleinschmidt Black & Akber, 2011）。钻井每天的平均水量为 35 万升，最高达到每天 63 万升。地下水和污泥中镭-226 和镭-228 的浓度如下： 镭-226 镭-228 水(钻孔) 1 Bq/L 0.7 Bq/L 污泥（池中废物） 2830 Bq/kg 2010 Bq/kg 信息栏 3.4：应急情况后污泥中活度浓度示例 日本福岛第一核电站事故后 日本传统的水处理工艺包括絮凝、沉淀、快速砂滤等。因此，福岛第一核电站事故发生 后，放射性铯集中在废污泥中。许多水处理厂都必须在事故发生后的头几个月保留这些污泥， 因为放射性铯的浓度非常高(污泥中> 8000 Bq/kg)。污泥不能在正常填埋场处置，需要作为放 射性废物储存；直到事故发生大约一年后，才建了一个处置放射性污泥的处置场。 英国在切尔诺贝利核电站事故之后 在英格兰西北部的一个饮用水处理厂，切尔诺贝利核事故后测到了污泥中的高活度浓度 （Jones & Castle, 1987）。测定表明，所采用的处理（絮凝和过滤）去除了污泥中的钌和放 射性铯。5 个月后，由于水源处理中短寿命放射性核素的稀释（131I 和 132Te)，污泥中活度浓 度明显降低。 废物泥中的活度浓度（Bq/kg） 放射性核素 1986年5月 1986年10月 103Ru 1900 24 131I 900 不可察觉 134Cs 350 17 137Cs 600 24 132Te 900 未检出 说明：钌-103（103Ru）、碘-131（131I）、铯-134（134Cs）、铯-137（137Cs）、碲-132（132Te） 德国在切尔诺贝利核电站事故之后 切尔诺贝利核事故后柏林也检测了污泥饼中的活度浓度（BMU, 1987; SSK, 1988）。虽然 当时测量了废水处理厂，而非饮用水处理厂，但也能说明事故后随着时间快速降低了活度浓 度，1986 年 5 月 11 日（事故后两周），暴雨将污染物从环境冲入污水系统，测量了最高的 活度浓度。英国此示例，经过处理的污泥饼中的活度浓度数月后快速降低。 3.4处理含放射性核素水的工作人员有何健康风险？ 如果在饮用水处理厂中，处理的水中含有放射性核素，从事水处理工作的人 员可能会在从事日常工作或进行例行维护时受到照射，照射的主要来源将是接近 或无意中摄入废物处理材料中的放射性核素，特别是由于过滤器和过滤器材料的 絮凝和反冲洗而产生的污泥。但是接触这些材料极不可能对这些工人构成任何重 38 大的健康风险。USEPA（2005）和Brown，Hammond＆Wilkins（2008a）中描述了 从事水处理活动的信息。Brown，Hammond＆Wilkins（2008a）中也提供了有关 如何剂量评估承担水处理工作的人员的指南。 如果供水行业的工人担心照射，应寻求专家意见。 供水行业可能需要对水处理厂的工作人员评估其来自于辐射照射的潜在的 健康风险作为应急计划的一部分，为使在发生核或放射事故后可以在短期内控制 照射，在不发生事故的情况下也有必要这样做。信息栏3.5讨论了用于评估水处 理厂工人影响所采用的测量。 信息栏 3.5 英国发生事故后水处理厂工作人员可能的剂量示例 在英格兰西北部的处理厂，切尔诺贝利事故后在污泥中测出了高活度浓度的铯-137（见 3.3中的信息栏3.5）。测量表明所用的处理（絮凝和过滤）去除了钌和放射性铯。当时担心 工人因某些操作比如清理污泥槽而吸入放射性核素摄入面临危险，然而监测表明剂量非常小， 而且污泥是湿的，减少了粉尘的吸入使得剂量变小。1986年10月（五个月后）进一步测量了 污泥中的活度浓度，证实进入处理厂的水已被稀释，污泥中的活度浓度低得多。 Brown，Hammond＆Wilkins（2008a）使用测量污泥的值和水处理厂的工作情况、水流 量的默认假设对日常工作人员进行保守剂量的估算。估算中使用了所测污泥中最高的活度浓 度值，估算剂量非常低（每周0.03 mSv），随后污泥中的活度浓度值随时间而降低（见信息 栏3.4）。 3.5采用哪些方法测量供水中的放射性核素？ 识别饮用水中具体放射性核素并测定其活度浓度的过程既耗时又昂贵。在非 应急情况下，定期常规监测中采用一种实用方法，即筛查法，该方法是初筛α和β 辐射的总放射性。总α和总β筛查方法依据放射性核素的放射性衰变过程中发射α 或β射线进行检测。该方法适用于饮用水中可能存在放射性核素的大多数情况。 传统上方法采用气体正比计数器测量总α和总β，并且仍然是世界上许多实验 室使用的标准计数测量方法。液体闪烁计数器的使用在不断增加，该技术更适合 测量地下水（通常地下水的固体总溶解量高），并且可能消耗较少的资源。液体 闪烁计数法能够测量β射线的放射性核素，不管其发射的能量如何。而气体正比 计数器仅限于测量较高的β能量。不过这两种方法都适合测量总α和总β的活度浓 度，跟筛查水平进行比较。总β测量包括了钾-40的贡献，如果超过总β筛查水平， 则应减去该部分（见1.5.3和1.5.4）。GDWQ第9章的表9.3提供了使用气体正比计 数器分析饮用水中总α和总β活度浓度的标准方法。 总α和总β筛查法根据α射线和β射线仅给出总放射性活度而无法获得放射性 核素的特性。应强调由于所采用的测量方法的差异及其测量不确定度，放射性核 素的活度之和对饮用水中总活度浓度的贡献非常不可能与总放的结果相吻合，特 别对于总β放射性，这是因为所采用的计数技术存在差异，以及测量中的相关不 确定性 测量具体放射性核素的方法 当需要测量特定放射性核素单一的活度浓度时，测量方法取决于放射性核素 及其发射的辐射类型。高分辨γ谱是定量检测许多发射γ射线的天然和人工放射 性核素的标准方法，它属于非破坏性测量，只需将样品装在合适的容器中无需其 39 它任何处理能直接测量饮用水样品。超纯锗探测器系统是高分辨率γ谱的主要构 造，但在测量天然水中常见放射性核素的活度浓度时可能需要浓缩样品。在核或 放射应急情况下高分辨率γ谱法最有可能是第一选择的测量方法。 如果γ谱可供使用，则可以作为一种筛查方法直接测量单一的发射γ射线的 放射性核素，因为大部分放射性核素发射γ射线。用该方法测量的单一放射性核 素应与指导水平相比较而不是与筛查水平比较。但是，γ谱无法检测出非应急情 况下饮用水中可能存在的所有放射性核素，特别是天然存在的只能通过总α和总β 法检测。 为了识别和测量绝大部分的发射纯α或β射线且不产生或产生非常弱的γ光子 的放射性核素，需要例如α谱，液体闪烁计数或其他β计数的方法。测量通常需要 经过放射化学法将放射性核素预处理提取为可测量的形态。 电感耦合等离子体质谱法（ICP-MS）是一种灵敏、高效且多元素同时分析的 方法，用于测量环境介质包括饮用水中的放射性核素。ICP-MS因其高灵敏应用越 来越广泛，因为直接测量放射性核素的原子数而非射线。这种技术对于放射性半 衰期很长的放射性核素特别适用，例如铀-234和铀-238，因为这些放射性核素单 位质量产生的放射性衰变数很小，因此很难通过其放射性进行测量。 饮用水中氡的测量包括在1.6部分。 应该使用已认证的分析方法进行测量，最好在公认的质量标准下进行，例如 ISO/IEC 17025：2005（ISO，2010），ISO/IEC 17025：2005 应用于实验室质量管 理体系建设，包括管理和技术要求，还有测量的质量控制，该标准还要求实验室 达到能力验证（内部和外部）以确保所用方法有效且测量结果具有一致性。 各种分析方法和测量技术的检出限取决于许多因素，主要是所使用方法和设 备及计数时间。一个国家采用的标准可能会规定检测限，以确保可以根据指导水 平（或国家标准）放心地评估样品中的放射性核素活度浓度，同时考虑到测量不 确定度。（见信息栏 3.6 示例） 表 3.3 总结了不同测量方法的主要特性。所表达的信息是相对而言而非绝对 值，这要取决于具体情况。GDWQ 附件 6 中特定放射性核素的分析方法供参考。 信息栏 3.6：欧盟饮用水水质指令中用于测量放射性核素的分析方法检出限的要求 例如，欧盟饮用水水质指令（EC，2013）规定了用于测量单一放射性核素的分析方法应 达到的检出限。通常，这些浓度比导出浓度（相当于 GDWQ 中的指导水平）低约 10 倍。对 于总 α和总 β活度浓度，要求检出限为筛查标准值的 40％。 表 3.3 测量饮用水中放射性核素的不同方法主要特性 特点 分析方法 注释 总α/β ICP-MS 谱（高分辨） β计数 α计数 通常 筛查法：总α粒子 和总β粒子（发射α 和β射线）的放射 性核素，不包括某 些放射性核素的 贡献（见1.4.3） 对半衰期长的 放射性核素有 效。特别适用 于234U、238U。 发射射线的放射性核素，如 134Cs、137Cs、131I、241Am，无 法测量很多天然放射性核素， 如 234U、238U、210Po。 226Ra 和 228Ra可以使用低能 探测器检测并假定与其它放 射性核素达到平衡。 对于226Ra，必须确保样品中的 准确测量大多 数β发射体的 放射性核素， 如90Sr、3H、14C。 准确测量大多 数α发射体的 放射性核素， 如239Pu、 210Po、 210Pb （通过210Po） 低分辨率谱可以作 为应急情况下的筛 查方法，比如NaI探 测器可以对样品提 供大致的活度浓度 标示，但通常无法提 供具体放射性核素 的信息。 40 氡未损失。 低分辨谱（如NaI探测器）可 应用于应急情况下的筛查。 速度（测 量时间） 几小时-几天（取 决于样品制备时 间）。 数小时 数小时 几天—几周 几天—几周 标准方法，可提供快 速法，但可能影响实 际的检出限。 制备样品/ 样品大小 在样品盘上蒸发 样品用于流气式 正比计数器。 液体闪烁计数法 要求样品浓缩到 小体积 （10-15ml）。 饮用水样品直 接测量，这样 就可以在同一 样本上进行进 一步的分析， 而不会使性能 下降。 饮用水样品直接测量，这样就 可以在同一样本上进行进一 步的分析，而不会使性能下 降。然而，灵敏度的问题，特 别在非应急情况下测量饮用 水中常见的放射性核素，因此 样品需要预浓缩。 测量前进行放 射性核素的复 杂化学分离。 测量前进行放 射性核素的复 杂化学分离。 高盐水样对总α测量 产生不利影响，总溶 解固体对采集α射线 的计数有屏蔽效应。 检出限 高 低（相比于其 它测量单一放 射性核素的方 法）。 高（相比于总β和总α测量技 术）。 低（相比于γ 谱） 低（相比于γ 谱） 训练水平 中-高 中等 中-高 高 高 γ计数的结果分析 需要中等培训水平， 样品制备为低培训 水平 样品通量 高 高 高-中 低 低 总的测量时间取决 于检出限的需求（非 应急情况下的低水 平测量需要预浓 缩）。 每样品的 成本 低 低 低 高 高 不包括设备采购。 设备费 中 高 高 中 高 关键核素：铀-234（234U）、铀-238（238U）、铯-134（134Cs）、铯-137（137Cs）、碘-131（131I）、镅-241（241Am）、钋-210（210Po）、 镭-226（226Ra）、镭-228（228Ra）、锶-90（90Sr）、氚（3H）、碳-14（14C）、钚-239（239Pu）、铅-210（210Pb）和碘化钠（NaI）。 应急情况其它信息 另外高分辨率γ谱、低分辨率γ谱在应急情况下可以用于筛查方法，比如碘 化钠（NaI）探测器可以对样品提供大致的活度浓度信息，但通常无法提供具体 放射性核素的信息，除非已知是γ放射性核素并且易于互相区别。 在应急情况下，水中的活度浓度可能比非应急情况下的活度浓度高很多；对 于所使用的分析方法，可以接受更高的检出限。这意味着可以通过减少样品制备 时间和减少某些放射性核素的计数时间来更快地获得测量结果。这些快速方法需 要作为应急准备工作的一部分，因为有必要非常迅速地采用标准分析方法以对应 41 急情况做出快速响应。某些放射性核素（例如锶-90）仍将需要放射化学方法以 将放射性核素分离为可以测量的形态。 如果在应急情况后的国家/地区中具有使用高分辨率γ谱检测的能力，并且 重要的放射性核素可以通过γ谱法测量，例如铯-137 和铯-134，则最好继续使用 γ谱，当情况恢复到非应急情况时进行谱分析，而不是采用总 α和总 β筛查方法 （见信息栏 3.7 示例）。 信息栏 3.7：在日本使用γ谱而不是总 α和总 β筛查方法的示例 在福岛第一核电站事故发生后，日本研制了性能更宽的γ谱仪并应用于测量饮用水中的 放射性核素。一种高分辨的 γ 谱仪自动测量系统于 2015 年安装应用于疏散令解除后的水处 理厂，该仪器可以每小时自动定量测量处理后的饮用水中铯-134 和铯-137 的活度浓度。 42 4 案例分析 4.1巴西 背景 在巴西一些天然辐射较高的地区，地下水中的放射性核素活度浓度可能超过 了 WHO 的指导水平和 0.1mSv/a 的个人剂量标准（IDC）（WHO，2017a）。这 种情况发生在位于巴西巴伊亚州东北地区的卡埃蒂市，发现几个铀异常（出现铀 高于本底）地点；迄今为止已绘制出 36 个点，分布在 1200 平方公里的区域。自 2000 年以来，利用该放射性异常开展了铀矿开采和水冶，并且自 1989 年开展了 环境监测计划。自 1989 年以来开展了环境监测计划。在该地区工业开始运营之 前，已报道过一些地下井水中铀的浓度很高。尽管卡埃蒂特的人口仅约 50,000， 但其中 40％的人口生活在农村地区，这些异常的地下供水是其饮用水的主要来 源。 2008 年，非政府组织谴责铀矿业污染了地下水，因为测量该地区一些井水 的总 α 和总 β 放射性结果超过了 WHO 基于 0.1 mSv/a 的 IDC 筛查水平，结果这 些井被地方当局关闭，直到进一步的调查，这种情况成为了非政府组织与铀业、 卫生部以及巴西核能委员会之间争执的焦点。巴西核能委员会认为：i）WHO GDWQ 筛查水平的说明和适用性具有误导性；ii）在做出任何决定之前，应进行 单一放射性核素的测量；iii）在该地区铀业运行之前，就已报告这些地下井水中 放射性核素活度浓度很高；iv）关闭水井的决定弊大于利，因为这是该村庄人口 最重要的饮用水来源。 饮用水的监管框架与责任 在巴西，卫生部通过 MS 2914/2011 号决议（巴西卫生部，2011）对饮用水 中微生物，化学和放射污染物进行监管，该决议要求每个供水系统必须分别分别 按照 0.5 Bq/L 和 1.0 Bq Bq/L 的筛查水平监测总 α 和总 β 放射性。如果超过了筛 查水平，则应测定单一放射性核素的活度浓度并与镭-226（1.0 Bq/L）和镭-228 （0.1 Bq /L）的最大允许值进行比较，该决议还指出，根据巴西核能委员会的要 求，应尽量调查其它放射性核素。 在巴西，有三种类型的供水系统： 1）大型供水网络系统，由每个城市或地区的水商运营； 2）一种可供选择的集中供水系统，包括没有配水网络的地表或地下水； 3）一种独立的供水系统，通常收集地下水仅供一个家庭或亲属使用。 前两个系统在监管之中，独立的供水系统则不受管制。负责饮用水质量的主 管当局对前两个系统要每六个月向公共卫生市政当局提交有关饮用水中放射性 核素的监测结果。 情况描述和应对措施 2008 年非政府组织提出投诉之后，6 口井被关闭，不幸的是政府无法向受影 响的社区维持供水，这些对社区造成了很大的社会影响（例如，人们不得不走很 长距离才能从其它水源取水）。辐射剂量是巴西核能委员会根据对单一放射性核 素的测量估算的，监测了 10 个村庄的几口水井，估算的平均剂量为 0.07 至 0.5 43 mSv/a 范围。由于天然铀浓度高于 WHO 对饮用水中铀毒性的指导值（30g/L）， 因此关闭了其中一个村庄的两口井。巴西核能委员会与市政卫生局联合发布了一 份公告，对情况进行了全面审查，并解释说，尽管某些水井的估算剂量超过了 WHO IDC 的 0.1 mSv/a，但仍低于 BSS 的参考水平 1 mSv/a（IAEA，2014）， 不能被视为不安全饮用。本公告的目的是向市政卫生局提供技术支持，使其能够 重新开放年剂量高于 0.1 mSv/a 但低于参考水平 1 mSv/a 的已关闭的井，要求继 续监测放射性核素，并使用 1 mSv/a 的参考水平将剂量保持在合理可达到的尽可 能低剂量。 这些事件之后，很明显需要重审巴西饮用水中放射性核素的准则。为了讨论 这些事件并提出对饮用水放射性国家立法的修订审查，巴西核能委员会的辐射防 护与剂量学研究所（IRD）举办了一次水质和放射性的专题讨论会。本次研讨会 联合国家监管部门、供水公司、分析服务机构和水质研究机构以及 WHO 和 IAEA 代表共同讨论饮用水监管中放射性方面包括国际建议等，主要是 WHO 的 0.1 mSv/a IDC 和 BSS 中的参考水平 1 mSv/a 的作用。由于缺乏与利益相关者之间清 晰的沟通，导致 2010 年和 2015 年出现了新的压力事件，例如其他井水超过了总 α和总β筛查水平和 WHO 的 0.1 mSv/a IDC，所致这些井被关闭。 成果 根据全国水质和放射性专题研讨会上的讨论，巴西核能委员会成立了一个工 作组，以修订巴西饮用水标准中的放射部分。 该工作组建议卫生部对饮用水的放射部分采用以下准则： 必须对每个供水系统的总 α 放射性和总 β 放射性进行筛查（筛查水平分别 为 0.5 Bq/L 和 1 Bq/L）。 如果总 β 放射性超过了筛查水平，则应减去钾-40 的贡献。 如果超过了总 α 和总 β 放射性筛查水平（减去钾-40 后），则应新采集样品 并进行分析。 如果新测量的总 α 和总 β 放射性仍大于筛查水平，则应将这些结果连同采 样位置和供水类型（地表水或地下水）一起转发给巴西核能委员会。 巴西核能委员会应确定这些样品中必须检测哪些天然或人工放射性核素， 并要求提供有关供水的其他信息。 放射性核素的专项测量结果应转发给巴西核能委员会，根据饮水量以估算 所致的总剂量，并评估水是否可以安全饮用。 评估结果如果总剂量低于参考水平 1 mSv/a，可能表明无需采取任何措施， 尤其在一些情况下 0.1 mSv/a 的 IDC 并不是可实际应用的标准。 国家水质标准（MS 194/2011 号决议）正在修订中，以纳入工作组提出的这 些新准则。但是，由于迄今为止尚未在政府机构与受影响的社区之间以及与非政 府组织之间建立有效的沟通方案，因此该社区仍然易受发生到此类新事件。 从巴西卡蒂特的这些事件中获得四个教训： 所采纳的用于管理饮用水中放射性的准则必须与不同的法规机构保持一致； 超过筛查水平或 IDC 并不一定意味着饮水是不安全的。如果这些标准被曲 解，有必要为政策制定者和水供应商提供如何解释和使用标准的指南/说明。 44 不同监管机构之间的协调与对话至关重要，例如在这种情况下，巴西核能 委员会、巴西环境与可再生自然资源研究所、巴伊亚州水管理与气候研究 所以及巴伊亚州卫生部。 风险通报是国家饮用水中放射性核素管理计划的重要组成部分。铀矿开采 经营者和监管者都需要与社区进行系统和体制化的沟通方案，包括公开听 证会（许可程序中指定的）以确保所有利益相关者的参与。制定风险沟通 方案可以减少该社区受此类事件的伤害。 4.2 加拿大 背景 在新斯科舍省，大约 50％的人口饮用水主要来自地下水。1978 年发现地下 水中高水平的天然铀，针对这一发现，成立了省级的专责小组，随后在 80 年代 对 700 多口水井测量了放射性核素，在新斯科舍省，测量饮用水中的铀已成为常 规监测，但通常并没有监测其它大多数天然放射性核素，饮用水系统常规测量总 α 和总 β 放射性。 饮用水的监管架构和责任 在加拿大，确保饮用水供应安全的责任由省（10 个省份）、地区（三个地 区）、联邦和市政府共同承担。省政府是所有饮用水供应的监管者，为公众提供 安全饮用水的日常责任通常由各省和地区的当局负责，而市政当局通常负责处理 厂的日常运行。 联邦-省-地区饮用水委员会（由每个辖区负责饮用水质量的主管部门成员组 成）与加拿大卫生部共同制定了加拿大饮用水质量准则（加拿大卫生部，2009）。 这些准则涉及微生物、化学和放射性污染物，还涉及了水的物理特性，比如味道 和气味。在最大可接受浓度下假定每天饮水量 2 升，按 1 年饮水量的参考剂量水 平 0.1 mSv 计算天然和人工放射性核素的最大可接受活度浓度。 情况描述和响应 在 2002 年 5 月的一项环境评估中，测量了饮用水中的总 α 和总 β 放射性， 新斯科舍省 Hubley 的一所学校的井水中总 α 放射性超过了加拿大的 0.1 Bq/L 筛 查水平（当时有效的筛查水平）。后续开展的详细分析结果显示，除铅-210 以外， 所有天然放射性核素均低于加拿大标准的值。 教育部采取了特别的预防措施，以确保 Hubley 学校周边的学生和教职员工 的饮用水安全。在 2002 年 5 月 29 日的一则新闻中，教育部表示：“我们非常重 视学生的健康和安全，虽然我们没理由相信其他学校存在问题，但是对饮用水进 行检测是负责任的预防措施，我们不会让孩子们去冒险”（Department of Education, 2002)）。负责该地区的省卫生官员在第一次新闻发布会上还表示，继续饮用 Hubley 学校初步样本中检测到铅-210 水平的饮用水不会造成公众健康风险，他 解释说，初步结果仅表明需要进一步调查，发布会上宣布已对圣保罗的 13 所学 校立即开展了检测，从圣玛格丽特湾至鲱鱼湾检测天然放射性核素（铀-234，铀 -235，铀-238，钍-228，钍-230，钍-232，钍-234，镭-224，镭-226，镭-228，铅 -210，钋-210，铋-210，铍-7）。 45 针对这一发现，环境与劳工部迅速成立了一个政府间特殊井水咨询小组，并 由其领导。2002-2003 年，在公立学校市政供水和注册的公众供水系统中启动了 全省范围的采样计划，以测定各放射性核素的水平，并确定该省饮用水中最可能 存在较高放射性核素水平的地区及地质构造（Drage，Baweja＆Wall，2005a; Drage， Baweja＆Wall，2005b）。 全省范围的放射性监测计划采取了分级方法。2002 年 6 月，对 52 所学校的 饮用水进行了初步抽样检测，发现其中 12 所学校的 210Pb 水平高于加拿大卫生部 的饮用水标准（0.2 Bq/L），在这 12 所学校中有两所的总铀也超过了加拿大卫生 部的饮用水标准（0.02mg/L）。检测结果使得 2002 年 9 月又启动了一项扩展监 测计划覆盖全省的学校（总计 184 所）。 184 所学校中有 178 所学校是地下水供水，有 6 所是地表水供水。放射性检 测仅测量了地下水供给的学校。结果证实铅-210 和总铀超过饮用水标准：178 个 学校水井中的 16 个学校（9％）的水井中铅-210 超标，3 个学校（2％）的水井 中总铀超标。 根据在全省范围监测计划中检测到的放射性核素水平，预期家水井和公共供 水预期需要关于如何处理饮用水中 210Pb 和铀的信息，由于铀的水处理系统已普 遍使用并可以获得，因此对 210Pb 的处理方法进行了评估。 一篇文献综述指出反渗透和离子交换处理系统可能是处理 210Pb 的最实用的 方法。现场评估计划是在 210Pb水平超标的几所学校启动，以确认这些系统的 210Pb 去除效率。现场评估的结果表明，两种处理方法对 210Pb 的去除率均低于 29％， 并且无法有效降低 210Pb 的水平。但一旦添加了活性炭或曝气，去除效率就会大 大提高（Drage，Baweja＆Wall，2005b）。 通过曝气去除水中的氡，可将 210Pb 的水平降低 90％以上。这表明当刚从井 中取水饮用时，极少有 210Pb 存在，而大部分 210Pb 是从从井中取水到分析之间 的时间由氡的衰变产生。对采样方案进行了相应的修改，即在采集水样时进行 10 分钟的鼓气，可以除去地下水样品中的氡，以消除实验室分析过程中饮用水 中氡的放射性衰变引起 210Pb 的产生。 前期调查 210Pb 超标的所有学校都重新使用新的采样方案，样品重新检测， 结果得出的结论是在新斯科舍省并不是一个重大问题，但是如果在饮用前含有氡 的储水中可能会导致超过指导值。对检测 210Pb 的这种新的理解为许多其他辖区 评估饮用水中 210Pb 的水平提供了宝贵的经验。 210 Pb 项目提出了饮用水中氡的潜在问题及使用含氡水导致室内空气中氡照 射的最重要问题。作为一项预防措施，2004 年夏季进行了室内氡的测量并作为 对解决学校饮用水中放射性问题的扩展工作，结果显示学校空气中氡的水平低于 加拿大空气中氡的标准。 成果 210 Pb项目通过主动面对问题挑战，而不是轻视遇到的问题而获得了信誉。 沟通对于该项目至关重要，尤其是最初在学校发现该问题，项目团队即使尚未 获得最终结果也会经常报告，团队保持开放和诚实获得了信任。在2002年至2004 年之间，总共发布了10则新闻（Department of Environment and Labour, 2004）， 首先是由教育部发布，而后是环境与劳工部，所有新闻发布中，该地区的医疗 卫生官员是有效的沟通者。2004年9月21日最后新闻发布中宣布环境劳动部已经 建立了免费直拨电话，可以获取井水中放射性核素和氡的信息。 46 4.3 约旦 背景 约旦是一个严重缺水的国家，生活用水的 80％由地下水构成，该水源的开 采量已超过安全产量的 160%。为了增加供水，特别是在高需求地区的供水，2005 年至 2009 年之间开发了 Disi 输水项目“建造-运行-输送”。该项目每年从约旦 南部沙漠的 Ram 地下水层的 55 口井中提取 1 亿立方米的地下水，这些水通过直 径 1.7 m、长度 320 km 的输送管输送到首都安曼（400 万居民）。 2013 年 6 月，由于有 130 万叙利亚难民涌入后的高需求，因此 Disi 输水项 目开始以应急方式向安曼首都提供 7000 万 m3/年的供水。2014 年 1 月，Disi 输 水项目开始向安曼供应全部容量为 100 m3 /年的水，将地下水层的水与足够量的 可持续来源地表水混合（图 4.1）。 目前正在实施一项扩建工程，该工程将在 2017 年至 2018 年期间最终服务于 约旦总人口的 75％，并将满足该国北部日益增长的需求。 饮用水的监管架构和责任 在约旦，卫生部是饮用水水质的监管机构。约旦负责供水的水务局和卫生部 共同负责确保向公众提供安全饮用水。卫生部负责从水流域到消费者的监测监督。 水质高层委员会对水质相关问题发挥咨询作用。该委员会主席来自学术专家 代表，成员包括有关部委，委员会制定水质管理标准和手册，并提供在修订水质 标准时应考虑的建议。 通过来自卫生部等不同组织的国家专家团队，约旦标准与计量组织制定并审 查了约旦国家标准，包括饮用水标准 JS286，该标准规定了饮用水中物理、化学、 放射和微生物参数的限值、参考水平、采样频次以及供水链中的选点，还规定了 在违反或超出所列各参数情况下所需采取的行动和干预措施。JS286 最新版于 2015 年发布，自 2016 年 5 月 1 日起生效。 对于放射性水质管理，Disi 输水项目公司制定了《环境与社会管理计划 第 二部分》（ESMP2）的第 2 部分，由约旦水务局实施。ESMP2 定义了用于监测 和混合的水质合规性要求，反映了 GDWQ 和约旦饮用水标准要求。 约旦水务局和卫生部共同制定了一项草案，包括详细的监测计划和管理措施 要求，以确保向客户提供的混合供水始终符合 JS286 和 ESMP2 的要求。 情况描述和响应 2001 年至 2009 年对 Ram 蓄水层地下水进行的水质调查显示，总 α 和总 β 活度浓度高于筛查水平，主要因为存在天然的放射性核素镭-226（226Ra）和镭-228 （228Ra）。Ram 地下水的平均剂量在 0.65-0.75 mSv/a 范围，其中 228Ra 的剂量占 70-85％。 因此，约旦政府要求世界卫生组织就以下方面提供技术和规范指导：i）审 查约旦饮用水放射性国家标准中的参考水平；ii）在超出参考水平的情况下建议 的国家干预和管理措施。 在考虑了 WHO 的 GDWQ 并仔细审查了当地的环境、社会和经济状况之后， 2008 年约旦饮用水标准的参考水平从 0.1 mSv/a 提高到 0.5 mSv/a。新的参考水 47 平是根据以下评估进行调整的：潜在的健康风险是可以接受的，提供充足水的净 健康效益超过了水中放射性核素含量造成的潜在健康风险。。 2005 年至 2012 年间，约旦水务局考虑了管理方案以确保满足修订后的国家 饮用水标准的要求，从而获得安全的水。基于中试规模设计，对每个备选方案进 行了可行性研究。 通过环境和成本效益分析，考虑对 108 m3/a 的 Disi 输水项目的总产量进行整 治后，决定对于约旦最实用和可持续的选择是将 Ram 蓄水层的水（Disi）与可用 的低放射性地表水源混合，其可持续量如下：来自 Zai 的 9000 万 m3/a 和来自 Zara-Ma'en 供水系统的 4500 万 m3/a。 对于具体放射性核素高的小型集中供水，没有可用于混合的水，在获得卫生 部批准后，在井口处选择不同的处理方案，反渗透和离子交换树脂两种方法都已 在小型试点项目中使用。 图 4.1 显示了从水源到消费点的整个采样系统。约旦水务局要求 Disi 水运项 目公司提供季度进展报告。 图 4.1 输水系统的简化方案 采样和分析方案由约旦水务局制定并经卫生部批准，所涉及的放射性参数包 括每月监测的总 α、总 β、222Rn、226Ra、228Ra、210P 和每年监测的 224Ra，以确保 放射性参数满足 JS286 和 ESMP2 中的频次： 每季度从 Disi 工程井场的 55 口井中的每口井中抽取样品，评估放射性水平 随时间的变化趋势； 每个月在约旦南部 55 口混合井水在准许进入 320km 的主管道之前采集水 样； 在安曼的两个水输送点（安曼北部的 Dabuk 水库和安曼南部的 Abu Alanda 水库）混合之前，每个月采集 Disi 水的混合水样； 每年对 Zara-Ma'en 和 Zai 处理厂的混合水进行监测（总 α，总 β，226Ra 和 228 Ra 的历史记录始终低于分析的检出限）。 安曼主要水库出口处每个月测量饮用水混合后的混合样品。 岔轨区(TO) 输出 A 输出 B 水库 (A) Dabuk Dabuk 助推器 （SA-B） Dabuk 客户仪表 （SA/SC） Marqab 客户仪表 （SB/SC） Marqab 水库 达布客的北安曼输送网-供应 A（SB/SC） 南安曼的输送网—供应 B (SB or SC) 水库 B1 (Abu Alanda 1) 水库 B2 (Abu Alanda 2) 混合水 A (BA) 混合水 B (BB) 组合井场 48 每月从公共水库抽取一次复合样本，代表安曼不同配水区向消费者供应的 水。 约旦水务局遵循 GDWQ 中推荐的方法（图 9.2；WHO，2017），根据饮用 水中放射性核素的筛查和指导水平进行评估，并将结果每月报告（或在发生应急 情况时）发送给卫生部。约旦水务局和卫生部采取的干预措施符合批准的国家协 议，并符合 JS286 和 ESMP2 的要求。表 4.1 说明了分阶段进行干预的方法。 表 4.1 约旦监测饮用水中放射性核素后遵循的干预措施 剂量的参考水平为 0.5 mSv/a < 0.45 mSv/a：不采取行动，维持常规监测 ≥ 0.45 mSv/a：红线值，要警惕 0.5 mSv/a – 1.0 mSv/a：调查以降低剂量，同时保持供水 ≥ 1.0 mSv/a：这是停止供水并解决问题的行动限值 如果混合水超过年剂量 0.45 mSv，则约旦水务局必须立即通知卫生部和 Disi 输水项目公司（红线警告）。约旦水务局必须在发出通知后的三个月内对钻井开 展逐步采样，以确认和缓解问题，并在采取纠正措施时告知卫生部与 Disi 输水 项目公司。该协议规定，每年度停止混合的天数不得超过 46 天；这是基于历史 数据和计算而得，以确保满足 JS286 和 ESMP2 的要求，同时考虑到用于混合的 两个地表水源在洪水期间可能会关闭。 结果 约旦在管理“Disi 输水项目”中水的放射性时，在 WHO 的指导和支持下，采 用并实施了符合国情的解决方案。该项目的结果是现在对水进行了更频繁地监控， 从总体上对风险评估和水的管理更加有效。 自 2013 年开始运营以来，Disi 输水项目井场的 55 口井中每口井的总 α、总 β、226Ra、228Ra、222Rn、210Pb 的季度结果保持不变。210Pb 活度浓度一直低于检 出限，同时 222Rn 的活度浓度已经相当的低。 饮用水供水链的年辐射剂量（混合后分配和输送到消费点）约为 0.40 mSv/a。 该剂量低于 0.45 mSv/a 的红线值和 0.5 mSv/a 的 JS286 参考水平。 为了获得公众信任，关于约旦饮用水标准（和参考水平）的制定以及 Disi 输水项目的管理，组织了宣传活动并以透明的方式开展了风险评估。 尽管约旦当局已经评估了混合的有效性和消费者提水的安全，但仍有一些领 域需要解决： 评估饮用水国家标准值 0.5mSv/a 对于婴儿和儿童的长期健康影响。 评估短寿命放射性核素（如 224Ra）对健康的影响，尤其是约旦南部的小 型社区供水井，因为从提取到消耗的时间很短。 4.4 瑞典 背景 瑞典富铀地质为主，地下抽取的饮用水中很容易出现高浓度的天然放射性核 素，尤其来自基岩蓄水层的饮用水。铀-238 衰变链的天然放射性核素首先引起了 高度关注。氡是研究最多的放射性核素，然而饮用水中的铀的关注在增加。对该 49 衰变链系列中的其它放射性核素，例如钋-210（210Po）和铅-210（210Pb）了解有 限。尽管土壤和基岩中钍的浓度是铀浓度的三倍，但饮用水中钍-232 衰变链中的 放射性核素尚未开展研究（SGU，2016）。 大约 2000-3000 个运行的公用水厂使用地下水源，供水量大的公用水厂主要 由市政当局运营，也有大量供水的规模较小的私营公司。公用水厂中放射性核素 的浓度通常较低。 除公用水厂外，瑞典平时使用约 26 万口钻井和 14 万口挖井。钻井数量每年 大约增加 5000 口，约 120 万人每天用水取自这些私人井。关于私营井中饮用水 中放射性核素活度浓度的信息不足，多年来有个别的研究 (Salih, 2003; Skeppström, 2005; Ek et al., 2008)表明存在的严重问题，许多私人钻井中的放射性 核素活度浓度在很多情况下非常高。 饮用水中放射性的监管限值 在瑞典，国家食品局发布法规以确保为民众饮用水的安全。该法规包括饮用 水中微生物、化学和放射污染物的标准，适用于公用供水。国家食品局是中央机 构，不对水处理设施进行任何监督，市政当局承担这一责任。 瑞典是欧盟成员国，因此饮用水中放射性核素的使用标准符合《欧盟饮用水 水质指令》（EC，2013）中规定的要求。该指令旨在保护公众健康涉及公众饮 水中的放射性物质。对于公用供水，瑞典对氡的法规限值为 100 Bq/L，如果饮用 水中氡浓度超过该限值，则需要采取补救措施。对于铀浓度不应超过 30μg/L， 该值主要预防铀的化学毒性。对于从地下水中抽取的饮用水，自 2015 年 11 月起 要求强制性筛查总 α和总 β活度浓度，总 α和总 β的筛查水平分别设置为 0.1 Bq/L 和 1 Bq/L，如果超过了筛查水平，则需要进行具体的放射性核素分析。筛查参考 值（不包括氡和寿命短氡的子体）是基于个人剂量 0.1 mSv/a，假定每年饮水 730 升，在瑞典必须遵守个人剂量标准限值。 对于私人井，饮用水中放射性推荐规范有两项：如果氡的活度浓度超过 1000 Bq/L 和铀的浓度不能超过 30μg/L，要采取补救措施。 公用水厂饮用水中的放射性 瑞典自 1990 年代末常规分析的放射性元素只有氡。《欧盟饮用水水质指令》 要求控制指示剂量（EC，2013，替代了 98/83/EC 指令），2003 年瑞典的法规中强 制执行，但由于缺乏执行该指令的指导原则，因此未能严格按要求执行。瑞典辐 射安全局和国家食品局于 2004 年启动了一个项目，目的是了解瑞典饮用水的状 况。该项目针对使用地下水（基岩蓄水层和土壤蓄水层）作为饮用水源并可能向 265 个城市提供饮水的公共供水。 该项目在饮用水供应量大的自来水厂采集了 256 个处理过的水样。对所有水 样进行总 α 和总 β 筛查分析，还测定了所有水样中的镭-226（226Ra）。大多数水 样（〜80％）的总 β 活度浓度低于检出限，仅 21 个水样超过了筛查水平 1 Bq/L， 但未开展具体放射性核素的分析确定是哪些放射性核素对总 β 的贡献。总 α 的活 度浓度有 65％的水样低于检出限，40 个水样超过总 α 筛查水平 0.1 Bq/L。为了 计算指示剂量，当未检测到 226Ra 的放射性时，假设所有 α 放射性来自铀。在发 现存在 226Ra 的样品中，铀的放射性是根据总 α 放射性和 226Ra 放射性之间的差 异推断出来的。几乎所有样品的 226Ra 均低于检出限。仅两个自来水厂（仅占所 研究水厂的 1％）的饮用水指示剂量超过 0.1 mSv/a。 50 这项研究得出的结论是自来水厂的饮用水中放射性核素活度浓度通常不会 超出指示剂量（Falk et al., 2004），不会带来健康风险，值得关注的是在该项目 仅研究了大约 3000 个水厂中的 256 个。但是自 2015 年 11 月《欧盟饮用水水质 指令》要求控制指示剂量（EC，2013）以来，所有相关自来水厂都在逐步分析和 评估饮用水中的放射性。国家食品局还创建了一个国家级数据库，以收集所有测 量结果和相关参数以评估数据。因此几年后将可以更好地描述公用水厂饮用水中 放射性问题。 饮用水中的放射性法规以及跟踪公用水厂饮用水测量数据的基础设施将用 于确保公众不会因饮用水中的高浓度活度放射性核素而受到照射，主要的挑战是 那些没有与公用供水系统相连的从私人井中获得供水的人。 私人水井饮用水中的放射性 瑞典约有 12％的人口从私人水井获得饮用水。2001 年瑞典辐射安全局与瑞 典地质调查局合作启动了私人井水中天然放射性核素的测绘项目。该项研究持续 了五年，有几个目标，其主要目标是获得私人井中的饮用水放射性的整体情况， 从而估算某些人群可能接受的潜在辐射剂量。另外两个目标是研究不同放射性核 素之间可能存在的时间变化和潜在相关性，时间变化和相关性的结果未在此处显 示。 该研究包括 722 口钻井。瑞典地质调查局的工作人员采集样品，绝大多数井 是在全县范围内随机选择，共覆盖 24 个县，也选择了已知地质结构中放射性强 度高的地区，使用地质图示对以前的研究进行了回顾以确定感兴趣的区域。研究 了位于拉特维克市的一个特殊区域 Siljan Ring，由于大约 3.6 亿年前发生过陨石 坠落，该地区具有独特的地质构造，位于该地区的私人井中铀含量像其他金属一 样非常高。 该研究采用的方法是在开展任何一个放射性核素分析之前先筛查总 α和总 β 放射性（氡例外），总 α 超过 0.1 Bq/L 时启动测量 226Ra 的活度浓度。铀的活度 浓度（238U，234U，235U）通过计算总 α 和 226Ra 的活度浓度之间的差异获得，通 过这些放射性核素的活度浓度计算指示剂量。铀浓度测定以 μg/L 表示为了可以 与管理限值比较，此处未显示铀质量浓度的结果。总 β 超标并未开展具体的 β 放射性核素分析，尽管在个别样品根据 β 能谱中估计了铅-210（210Pb）的浓度。 假定指示剂量的主要贡献来源于铀-238 衰变子体的 α 放射性核素。 饮用水中 226Ra 的活度浓度通常较低，中位值为 0.02 Bq/L，最大值为 7.0 Bq/L。 发现铀（238U，234U，235U）的中位值活度浓度为 0.13 Bq/L，记录的最大值为 26.7 Bq/L。研究的井水中 2％铀的活度浓度超过指导值 3 Bq/L。 研究的井水中 8％的氡活度浓度超过 1000 Bq/L，供约 6 万人饮用，氡的最 大值和中位值分别为 66200 Bq/L 和 220 Bq/L。 对 620 口井进行了基于铀（238U，234U，235U）和镭-226 活度浓度的指示剂 量估算，发现 10％的指示剂量超过 0.1 mSv/a。在 Siljan Ring 附近，饮用水中所 有研究的放射性核素的活度浓度都很高，该地区绝大多数井的用水所致辐射剂量 超过 0.1 mSv/a。计算该区域最高剂量（包括 210Pb）为 5 mSv/a。 该项目的局限性在于水样中均未分析 210Pb（Siljan Ring 附近地区的一些样品 除外）和 228Ra，如先前研究所示瑞典的饮用水中可能存在这些元素（Salih，2003）。 这意味着从私人井中喝水的人群所接受的辐射剂量可能高于仅从铀和 226Ra 计算 得出的剂量。该项目的另一个局限性是尚未研究可能在一些样品中存在 210Po。 51 假定总 α 放射性来源于 226Ra 和铀同位素，这意味着在某些情况下，铀同位素的 剂量贡献可能被高估了。 结论与回应 对公用水厂和私人水井的研究显示某些私人水井明确存在隐患。如果结果显 示放射性核素的极端活度浓度（氡> 1000 Bq/L、铀> 3.0 Bq/L），则联系拥有这 些水井所有者并告知其问题。在拉特维克市 Siljan Ring 附近的研究区域也进行了 实地考察，检测到了最高活度浓度的镭和铀。市政当局的卫生督查以及县级的利 益相关者都被告知超标程度和问题的重要性，这使得该地区开展了更深入的研究 和当地的宣传活动。一项后续调查显示，在全国测绘项目之后，许多饮用水中氡 和铀浓度较高的参与者采取了补救措施。通常使用氡的曝气技术和铀的离子交换 过滤器。后续调查还显示，尽管许多私人井所有者参与了该项目，但他们对饮用 水中放射性的了解仍然有限，这突出了定期就环境中自然产生的放射性核素进行 风险沟通的必要性。 4.5 日本 背景 2011年 3月 11日东日本大地震和随后的海啸之后，东京电力公司（TEPCO） 的福岛第一核电站遭到了严重破坏，导致大量放射性核素释放到日本的环境中。 这些放射性核素的扩散和沉积受放射性烟羽通过期间气象条件的影响，特别是风 向和降水（例如雨，雪）。 国家主管部门已采取措施保护人们免受事故后果的影响，包括建立 20 公里 的疏散区和 30 公里的避难区。随着环境监测数据可用性的提高，还采取了其他 保护措施以减少剂量（WHO, 2012; WHO, 2013）。中央和地方政府以及自来水 公司对自来水进行了监测。2011 年 3 月 16 日，在一些自来水样品中首次检测到 碘-131，从 3 月 21 日开始，对包括东京在内的许多村庄和城市实行了自来水消 耗限制（MHLW，2011a）。但是由于碘-131 的半衰期很短（约 8 天），饮用水 中的活度浓度迅速降低；之后铯-134 和铯-137 是关注的主要放射性核素。 受影响的供水主要是来自地表水源的公共供水。通常，私人供水系统不受影 响，因为它们主要依靠地下水作为水源。 饮用水监管框架 在日本，饮用水的管理当局是厚生劳动省。厚生劳动省供水司制定了饮用水 水质标准及相关项目。放射性物质不在管制项目之列，但是自事故发生以来，厚 生劳动省已要求在福岛及周边 10 个县进行放射性物质监测。将来核监管局或厚 生劳动省将负责对饮用水的限制管理。 2011 年 3 月 17 日，厚生劳动省食品安全局采用日本核安全委员会的指导方 针，将其转变为核监管局，确立了国内食品中放射性核素活度浓度的临时监管值。 （根据 1947 年 12 月 24 日第 233 号法案《食品卫生法》）（MHLW, 2011b）。 饮用水（包括自来水，井水和瓶装水）被列为适用临时法规值的类别之一。提供 了碘-131，铯-134，铯-137，铀以及其他元素的核素规定值，没有设置总 α 和总 β 活度浓度的筛查水平。2011 年 3 月 19 日，供水司制定了限制自来水摄入量的 52 临时指标水平，该水平与临时法规值相同，但仅针对碘-131，铯-134 和铯-137 提供（MHLW, 2011c）。厚生劳动省通知地方政府当局和区域水供应商，理想 情况下不应该消耗超过临时法规值的受污染的自来水，如果不能获得替代的供水， 即使是婴儿也可以饮用（MHLW, 2011c）。 当前的标准（针对非应急情况）被称为“自来水中放射性物质管理的目标水 平”，于福岛第一核电站事故发生约一年后，2012 年 4 月 1 日确定（MHLW, 2012）。 情况描述和响应 在应急照射期间，福岛县和其他 10 个县被指定为主要监测区域，政府组织 要求对自来水中的碘-131，铯-134 和铯-137 进行密集测量。该地区的人口约为 5000 万，占日本总人口（约 1.26 亿）的 40％。许多政府组织、研究机构和供水 机构开始每天或更频繁地在水源测量方面进行合作，并使用高纯度锗半导体探测 器或碘化钠烁计数器测量自来水中具体放射性核素活度，主要为碘-131，铯-134 和铯-137。饮用水中所有放射性核素的测量浓度已通过厚生劳动省和各供水单位 的网站公开宣布。 为了应对应急情况，食品安全司于 2011 年 3 月制定了饮用水限制的暂行规 定值。碘-131 的临时调节值为 300 Bq/kg，放射性铯的临时调节值为 200 Bq/kg （铯-134 和铯-137 之和）。2011 年 3 月 19 日，供水司宣布了限制自来水摄入量 的临时指标水平，该水平与临时法规值相同，但仅提供碘-131 以及铯-134 和铯 -137 之和。3 月 21 日供水司还宣布婴儿的碘-131 临时指数水平为 100 Bq/kg （MHLW，2011d）。 自 2011 年 3 月 21 日起，有 20 家自来水公司要求限制婴儿的自来水摄入量， 这些自来水公司为包括东京都在内的大约 1,400 万人提供服务。东京都区域的限 制仅进行了两天（3 月 23 日至 24 日），其他地区的所有供水设施的限制均于 2011 年 4 月 1 日取消，除了福岛县的一个小规模供水的 Iitate 村（MHLW，2011a）。 自 2011 年 5 月 10 日起，向 Iitate 村供水的自来水公司取消了对婴儿自来水的限 制（尽管所有其他年龄组的限制都已在 2011 年 4 月 2 日取消）。没有供水机构 要求根据放射性铯（200 Bq/kg）的临时指标水平限制自来水的摄入量。 所有利益相关者（厚生劳动省、供水方、地方政府、媒体、当地居民等）之 间的交流与合作都得到了加强。还通过电视发布了关于限制婴儿使用自来水公告， 使用广告车进行地方政府广播等。但人们仍然担心应急情况下的健康影响，并对 公告不满意，市民打了许多电话给地方政府的卫生部门，供水方和相关组织。 当东京都会区宣布限制婴儿饮用自来水两天（2011 年 3 月 23 日至 24 日）， 瓶装水很快就在商店中售罄。东京都政府水务局在 3 月 23 日 21:00 举行的新闻 发布会上宣布，他们将为有 1 岁或以下儿童的家庭提供瓶装水，向生活在服务区 域的约 80,000 名儿童的家庭提供三瓶 550mL（总计约 24 万瓶）。 核电站事故发生约 10 天后，由于降水导致大量放射性物质从大气层沉积到 陆地上，这是污染水源的主要原因。因此降水后停止提取地表水会降低自来水中 放射性核素的浓度。在一些净化水厂，用塑料板覆盖露天水池进行水处理过程， 包括絮凝，澄清和砂滤，以减少干湿沉降直接对水造成的污染。（在日本，几乎 所有的水库都被覆盖以防止化学和微生物污染）。之所以采取这些措施，部分原 因是没有足够的证据表明活性炭处理和颗粒分离在去除水中放射性核素方面的 有效性。尽管随后的一些研究证实，前一种处理方法对于去除碘有效，而后一种 去除铯有效。覆盖仍然被认为是防止放射性核素污染的相对有效和实用的方法， 53 可以防止干/湿沉积物直接沉积在水面上。如上所述，对水中碘的有效处理是在 将水存储到处理池之前进行，且与放射性铯不同，砂滤不会去除碘。 以下为应急情况下管理饮用水中放射性核素的经验教训/建议： 立即应对核事故至关重要。有必要为应急情况下建立饮用水标准，这些标 准应作为应急计划和准备工作的一部分而建立。 尽管也可以在应急情况下使用常规饮用水监测中的总 α 和总 β 测量方法， 但这些筛查方法效率低下，主要是因为预处理过程中的挥发可能无法通过 总 β 方法测量碘-131。 在应急情况下测量饮用水中放射性核素的技术应成为应急计划的一部分。 在应对应急情况期间，优先使用 GDWQ 中的相关测量技术是不可行的。 在应急情况下，所有相关利益相关者之间的有效对话与合作至关重要，以 向公众提供有关健康风险、发展状况和已采取措施的明确信息。 2012 年 4 月之后的非应急情况（现存照射情况） 从 2012 年 4 月开始，就饮用水而言已被视为现存照射情况（疏散命令下的 区域除外，该区域不包括在本案例分析中）。2012 年 4 月制定了自来水中放射 性核素管理的目标水平。该目标水平取代了临时指导水平，并直接从 GDWQ 的 指导水平得出（请参见下文）。铯-134 和铯-137 的总和目标值为 10 Bq/kg，已 替代了先前的应急情况临时指导水平。放射性铯是唯一具有目标水平的物质，因 为核电厂事故中的碘-131 的影响由于半衰期相对较短（约 8 天）而从环境中消失 了。 长期问题包括以下内容： 在疏散令解除，回到家的居民仍有关于饮用自来水的风险沟通问题。尽管 净化后的水并未超过放射性铯的目标水平，仍有人担心自来水中的放射性 铯，因为一些净水厂从沉淀物被铯污染的大坝中取水。 人们担心长期的水环境污染行为，尤其是森林和山区中剩余的放射性铯向 地下水的转移。根据迄今为止的观察和预测，这不太可能发生。 处理水净化过程产生的污泥：核事故后产生的污泥中含有较高的铯-134 和 铯-137。在日本含有 8000 Bq/kg（铯-134 和铯-137 之和）的污泥不能在普 通垃圾填埋场处置。它需要作为放射性废物存储。 将 WHO 的铯-134 和铯-137 指导水平直接用于确定日本非应急情况（现有 照射）情况下的饮用水目标水平。但公众甚至饮用水部门的监管者和专家 都容易误解指导水平的含义和概念。他们通常将指导值视为最大允许极限。 因此有必要改善有关指导水平解释的交流。 54 参考文献 Annanmaki M & Turtianen T (2000). Treatment technologies for removing natural radionu clides from drinking-water. Final report of the TENAWA project, STUK-A169. Helsinki: Radiation and Nuclear Safety Authority (http://www.iaea.org/inis/ collection/NCLCollectionSt ore/_Public/32/018/32018426.pdf, accessed 28 September 2017). BfS (2009). Strahlenexposition durch natürliche radionuklide im Trinkwasser in der Bundes republik Deutschland. [Radiation exposure by natural radionuclides in drinking-water in the Federal Republic of Germany.] Eds. Beyermann M, Bünger T, Gehrcke K. und Obrikat D. Bundesamt für Strahlenschutz (Hrsg.), BfS SW 06/09, Salzgitter: 129 S (in German) (h ttp:// nbn-resolving.de/urn:nbn:de:0221-20100319945, accessed 19 October 2017). BMG (2016). Trinkwasserverordnung in der Fassung der Bekanntmachung vom 10. Mäz 2 016. BGBl, Teil I Nr. 12: S. 459–491 Federal Ministry of Health (BMG) German Drinkin g-Water Ordinance (in German) https://www.bundesgesundheitsministerium. de/topics/drinkin g-water-ordinance/?L=0, accessed 20 March 2018). BMU (1986). Gesetz zum vorsorgenden Schutz der Bevökerung gegen Strahlenbelastung (S trahlenschutzvorsorgegesetz – StrVG) vom 19. Dezember 1986. BGBL Teil I: S. 2610 (ge ädert in BGBL Teil I: S. 1474 vom 31. August 2015) Radiation Protection Precautionay Act (in German). Published in the Federal Law Gazette (BGBI Bundesgesetzblat). BMU (1987). Auswirkungen des Reaktorunfalls in Tschernobyl auf die Bundesrepublik De utschland. Gemeinsamer Bericht der Leitstellen für das Jahr 1986. Bundesminister für Um welt, Naturschutz und Reaktorsicherheit (Hrsg.), Bonn (in German). BMU (2001). Verordnung über die Umsetzung von Euratom-Richtlinien zum Strahlenschutz (Strahlenschutzverordnung – StrlSchV) vom 20. Juli 2001. BGBl., Teil I Nr. 38: S. 1714 –1846 Radiation Protection Ordinance (in German) Published in the Federal Law Gazette (BGBI Bundesgesetzblat). BMU (2006). Allgemeine Verwaltungsvorschrift zum Integrierten Mess- und Informationssy stem zur Überwachung der Radioaktivitä in der Umwelt (IMIS) nach dem Strahlenschutzvo rsorgegesetz (AVV-IMIS) vom 13. Dezember 2006. bundesanzeiger Nr. 244a: S. 4–80 (in German). Brown J, Hammond D & Wilkins BT (2008a). Handbook for assessing the impact of a ra diological incident on levels of radioactivity in drinking-water and risks to water treatment plant operatives. Chilton: Health Protection Agency (https:// www.gov.uk/government/uploa ds/system/uploads/attachment_data/file/340109/HPA-RPD-040_for_website.pdf, accessed 19 O ctober 2017). Brown J, Hammond D & Wilkins BT (2008b). Handbook for assessing the impact of a ra diological incident on levels of radioactivity in drinking‑water and risks to water treatment plant operatives: supporting scientific report. Chilton: Health Protection Agency (http://ww w.dwi.gov.uk/research/completed-research/reports/DWI70-2-192_supporting.pdf, accessed 19 Octo ber 2017). 55 Brown J, Watson S & Nisbet AF (2015). UK recovery handbooks for radiation incidents 2015. Drinking‑water supplies handbook. Version 4. London: Public Health England (https: //www.gov.uk/government/uploads/system/uploads/attachment_data/file/433689/PHE-CRCE-018 _Drinking_Water_Supplies_Handbook_2015.pdf, accessed 17 October 2017). Canada Nuclear Safety Commission (2016). Independent Environmental Monitoring Progra m (IEMP) [website]. Ottawa: Canada Nuclear Safety Commission (http://nuclearsafety.gc.ca/ eng/resources/maps-of-nuclear-facilities/iemp/indexiemp.cfm, accessed 19 October 2017). Chen, J, Cooke, MW & Mercier, JF (2017). A review of natural radionuclides in Canadia n drinking‑water (1975–16). Radiat Prot Dosimetry. 176(1–2):1–11. CODEX (1981). CODEX standard for natural mineral waters. CXS 108-1981. Rome: Food and Agriculture Organization of the United Nations, Joint FAO/WHO Food Standards Pro gramme, Codex Alimentarius Commission (www.fao.org/input/download/standards/223/CXS_ 108e.pdf, accessed 19 October 2017). CODEX (2001). CODEX general standard for bottled/packaged drinking‑waters (other than natural mineral waters), CXS 227-2001. Rome: Food and Agriculture Organization of the United Nations, Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commi ssion (www.fao.org/input/download/standards/369/CXS_227e.pdf, accessed 19 October 2017). EC (1998). Council Directive 98/83/EC on the quality of water intended for human consu mption. Brussels: European Commission (http://eur-lex.europa.eu/, accessed 19 January 201 8). EC (2013). Council Directive 2013/51/EURATOM laying down requirements for the protec tion of the health of the general public with regard to radioactive substances in water inte nded for human consumption. Brussels: European Commission (http://eur-lex.europa.eu/, acc essed 19 January 2018). El-Naser HK, Smith B, Kilani S, Abdeldin I, Howarth B, Saleh B (2016). Blending as th e best compliance option for the management of radioactivity in drinking‑water supplied fr om the deep sandstone aquifer in Southern Jordan. J Water Health. 14(3):528–48. Environment Agency et al. (2016). Radioactivity in food and the environment, 2015. Rothe rham: Environment Agency, Food Standards Agency, Food Standards Scotland, Natural Res ource Wales, Northern Ireland Environment Agency and the Scottish Environment Protectio n Agency (https://www.gov.uk/government/publications/radioactivity-in-food-andthe- environment- rife-reports-2004-to-2016, accessed 19 January 2018). EPA (2000). Radionuclides Rule under the Safe Drinking‑Water Act, 66 Federal Register 76708, December 7, 2000. Washington (DC): United States Environmental Protection Agen cy (https://www.federalregister.gov/documents/2000/12/07/00-30421/national-primary-drinking- water-regulations-radionuclides-final-rule). Health Canada (2017). Guidelines for Canadian drinking‑water quality—summary table. Ott awa: Water and Air Quality Bureau, Healthy Environments and Consumer Safety Branch, Health Canada (https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/ewh-semt/alt_formats/ 56 pdf/pubs/water-eau/sum_guide-res_recom/sum_guide-res_recomeng.pdf, accessed 19 October 2 017). Hess CT, Vietti MA & Mage DT (1987). Radon from drinking‑water – evaluation of wat er-borne transfer into house air. Environ Geochem Health. 9:68–73.IAEA (2011). Criteria f or use in preparedness and response for a nuclear or radiological emergency. IAEA (2011). Criteria for use in preparedness and response for a nuclear or radiological e mergency. IAEA Safety Standards Series No. GSG-2. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/Pub1467_web.pdf, accessed 17 O ctober 2017). IAEA (2014). Radiation protection and safety of radiation sources: International Basic Safe ty Standards. IAEA Safety Standards Series No. GSR Part 3. Vienna: International Atomic Energy Agency (http://www-pub.iaea.org/MTCD/publications/PDF/Pub1578_web-57265295.p df, accessed 17 October 2017). IAEA (2015). Preparedness and response for a nuclear or radiological emergency. IAEA S afety Standards Series No. GSR Part 7. Vienna: International Atomic Energy Agency (http: //www-pub.iaea.org/MTCD/publications/PDF/P_1708_web.pdf, accessed 20 October 2017). IAEA (2016). Criteria for radionuclide activity concentrations for food and drinking-water. IAEA-TECDOC-1788. Vienna: International Atomic Energy Agency (http://www-pub.iaea.or g/MTCD/Publications/PDF/TE-1788_web.pdf, accessed 27 November 2017). IAEA (2018). A arrangements for the termination of a nuclear or radiological emergency (GSG-11). IAEA-Safety Standards Series No. GSG-11. Vienna: International Atomic Energ y Agency (https://www-pub.iaea.org/MTCD/Publications/PDF/PUB1796_web.pdf, accessed 15 May 2018) ICRP (2009). Application of the Commission’s recommendations to the protection of peopl e in emergency exposure situations. Publication 109. Ann ICRP. 39(1)1–110. ISO (2006). ISO/NP 5667-1: Water quality – Sampling – Part 1: Guidance on the design of sampling programmes and sampling techniques. Geneva: International Organization for S tandardization. ISO (2010). ISO/IEC 17025:2005. General requirements for the competence of testing and calibration laboratories. Geneva: International Organization for Standardization. Iwaoka K (2016). The current limits for radionuclides in food in Japan. Health Phys. 111 (5):471–78. Jones F & Castle RG (1987). Radioactivity monitoring of the water cycle following the C hernobyl accident. Water Environ J. 1(2):205–217. Kleinschmidt R & Akber R (2008). Naturally occurring radionuclides in materials derived from urban water treatment plants in southeast Queensland, Australia. J Environ Radioact. 99:607–620. 57 Kleinschmidt R, Black J & Akber R (2011). Mapping radioactivity in groundwater to iden tify elevated exposure in remote and rural communities. J Environ Radioact. 102:235–243. Kosaka K, Asami M, Kobashigawa N, Ohkubo, K, Terada H, Kishida N et al. (2012). Re moval of radioactive iodine and cesium in water purification processes after an explosion at a nuclear power plant due to the Great East Japan Earthquake. Water Res. 46:4397–440 4. Kosaka K, Watanabe S, Kobayashi Y, Sasaki M, Asami M, Oikawa T et al. (2014). Rem oval of radioactive iodine and cesium by powdered activated carbon and coagulation-sedim entation processes [in Japanese]. Journal of Japan Water Works Association. 83(1):7–22. MHLW (2011). Handling of the index levels on radioactive materials in tap water, etc. (P ress release). Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, L abour and Welfare, April 4, 2011 (http://www.mhlw.go.jp/english/topics/2011eq/dl/april_8_01. pdf, accessed 31 January 2018). MHLW (2012a). Measures against radioactive materials in tap water. Tokyo: Water Supply Division, Health Service Bureau, Ministry of Health, Labour and Welfare (http://www.mhl w.go.jp/english/topics/2011eq/dl/Document_121011.pdf, accessed 31 January 2018). MHLW (2012b). Notice on the replacement of provisional index levels for restriction on t ap water intake [in Japanese]. Tokyo: Water Supply Division, Health Service Bureau, Mini stry of Health, Labour and Welfare (http://www.mhlw.go.jp/stf/houdou/2r98520000018ndf-att /2r98520000024of2.pdf, accessed 31 January 2018). Nazaroff WW, Doyle SM, Nero AV, Sextro RG (1987). Potable water as a source of airb orne Rn-222 in US dwellings: a review and assessment. Health Phys. 52(3):281.289. Ohno K, Ogata T, Kawamura S, Sato H, Kosaka K, Asami M et al. (2013). Behaviour of low level radioactive caesium ion during conventional water purification processes. Procee dings. The 8th International Water Association Micropol & Ecohazard, Zurich, Switzerland, June 2013:138.139. SSK (1988). Auswirkungen des Reaktorunfalls in Tschernobyl auf die Bundesrepublik Deut schland Veroffentlichungen der Strahlenschutzkommission . Band 7 [Effects of the reactor accident in Chernobyl on the Federal Republic of Germany. Publications of the Radiation Protection Commission]. Bundesminister fur Umwelt, Naturschutz und Reaktorsicherheit (Hr sg.). Stuttgart: Gustav Fischer Verlag (in German). Tagami K & Uchida S (2011). Can we remove iodine-131 from tap water in Japan by bo iling? Experimental testing in response to the Fukushima Daiichi nuclear power plant accid ent. Technical Note. Chemosphere. 84(9):1282.1284. UNSCEAR (2000). Sources and effects of ionizing radiation. Volume I: Sources. New Yor k (NY): United Nations Scientific Committee on the Effects of Atomic Radiation (http://w ww.unscear.org/unscear/en/publications/2000_1.html, accessed 20 October 2017). UNSCEAR (2008). Sources and effects of ionizing radiation. Volume I: Sources: Report to the General Assembly and Scientific Annexes A and B. New York (NY): United Nations 58 Scientific Committee on the Effects of Atomic Radiation (http:// www.unscear.org/unscear/ en/publications/2008_1.html, accessed 20 October 2017). UNSCEAR (2016). Sources, effects and risks of ionizing radiation. Annex D . Biological effects of selected internal emitters.Uranium. New York (NY): United Nations Scientific C ommittee on the Effects of Atomic Radiation (http://www.unscear.org/docs/publications/2016 /UNSCEAR_2016_Annex-D.pdf, accessed 20 October 2017). USEPA (2005). A regulators 乫 guide to the management of radioactive residuals from dri nking.water treatment technologies. Washington (DC): United States Environmental Protecti on Agency (https://www.epa.gov/sites/production/files/2015-05/documents/816-r-05-004.pdf, ac cessed 20 October 2017). WHO (2009). WHO handbook on indoor radon. A public health perspective. Geneva: Wor ld Health Organization (http://www.who.int/ionizing_radiation/env/9789241547673/en/, access ed 27 November 2017). WHO (2012). Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami. Geneva: World Health Organization (http://www.who.i nt/ionizing_radiation/pub_meet/fukushima_dose_assessment/en/, accessed 20 October 2017). WHO (2013). Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary dose estimation. Geneva: World He alth Organization (http://www.who.int/ionizing_radiation/pub_meet/fukushima_risk_assessment _2013/en/, accessed 20 October 2017). WHO (2017a). Guidelines for drinking-water quality, fourth edition incorporating the first addendum. Geneva: World Health Organization (http://www.who.int/water_sanitation_health/p ublications/drinking-water-quality-guidelines-4-including-1st-addendum/en/, accessed 27 Nove mber 2017). WHO (2017b). Iodine thyroid blocking: guidelines for use in planning for and responding to radiological and nuclear emergencies. Geneva: World Health Organization; 2017 (http:// www.who.int/ionizing_radiation/pub_meet/iodine-thyroid-blocking/en/, accessed 17 January 20 18). 59 附录 A 非应急情况特定剂量和指导水平的计算 A.1 儿童饮用水的剂量 如果超出指导水平则有必要进行进一步调查。这可能包括针对受影响人群的 评估，并且考虑其饮水习惯。如果长时间超过指导水平，则应评估对儿童和婴儿 食用饮用水冲调的瓶装牛奶的剂量。尽管儿童通常比成人消耗更少的饮用水，但 他们对某些放射性核素的照射更为敏感。 可以使用特定年龄的饮水量和摄入剂量系数来计算儿童剂量。 公式是：D = A×C×I 这里: D =年剂量（mSv/a） A =饮用水中放射性核素的活度浓度（Bq/L） C =相关年龄段的饮水量（L/a）；见表 A.1 I =相关年龄组的摄入剂量系数（mSv/Bq）；见表 A.2 A.2 饮水量 不同国家和年龄的人饮水量差异很大，这取决于习惯和气候（Howard＆ Bartram，2003）。每天的饮水量在世界各地有所不同，尤其是在炎热气候下从 事体力劳动的消费者。因此，在有当地饮用水消耗数据的地方，使用这些信息计 算剂量很重要。如果没有本地或国家数据，则来自一个区域内邻国的信息可能比 全球平均数据更合适。研究是否将自来水用于制造婴儿瓶装奶也很重要。如果没 有则可以使用表 A.1 中给出的默认值来评估饮用水消耗对儿童的剂量。 表 A 1 儿童的默认饮水率 年龄 升/天 注释 参考文献 婴儿 (< 6 个月) 0.75 以 5 公斤体重为基础，用自来 水冲奶粉喂养的婴儿 WHO (2017) 小孩 1.0 以 10 公斤体重为基础，约 1 岁 的儿童 WHO (2017) 所有儿童 1.0–2.0 消费率在此范围内变化，取决 于习惯，体重和气候 IPCS (1994); Howard & Bartram (2003) 根据大量研究，《定量微生物风险评估：水安全管理应用》（WHO，2016） 中给出了特定国家平均饮水量数据的总结（WHO，2016）。确定了一些可能影 响消费数据分析和解释的重要因素，在进行此类调查时应考虑这些方面(WHO, 2016; Mons et al., 2007)。 60 A.3 儿童的摄入剂量系数 国际放射防护委员会（ICRP，2012）提供了包括儿童和婴儿在内的所有年 龄组的摄入剂量系数。表 A.2 中给出了 GDWQ 第 9 章（表 9.2）中列出的常见天 然和人工 放射性核素的值（WHO，2017）。其他放射性核素的值在 ICRP（2012） 中给出。应注意给婴儿的数值是针对那些牛奶喂养的婴儿，通常年龄小于 6 个月。 如果婴儿食用食物，则更适合使用 1 岁儿童的值。从表 A.2 中可以看出，1 岁和 10 岁儿童的值差异不超过 2 倍（碘-131 除外），所有儿童（不包括奶瓶喂养的 婴儿）被认为是一个单一年龄组，使用表 A.1 中饮水量来考虑剂量范围。如果饮 用水中含有碘-131，可能需要对剂量随年龄的变化进行更详细的评估。 表 A 2 不同年龄的摄入剂量系数 核素 剂量系数(mSv/Bq) 成人 婴儿 (<6 个月) 儿童 (1 岁) 儿童 (10 岁) 氚 1.8 × 10-8 6.4 × 10-8 4.8 × 10-8 2.3 × 10-8 碳-14 5.8 × 10-7 1.4 × 10-6 1.6 × 10-6 8.0 × 10-7 锶-90 2.8 × 10-5 1.3 × 10-4 7.3 × 10-4 6.0 × 10-4 碘-131 2.2 × 10-5 4.8 × 10-4 1.8 × 10-4 5.2 × 10-5 铯-134 1.9 × 10-5 2.6 × 10-5 1.6 × 10-5 1.4 × 10-5 铯-137 1.3 × 10-5 1.1 × 10-5 1.2 × 10-5 1.0 × 10-5 铅-210 6.9 × 10-4 2.4 × 10-3 3.6 × 10-3 1.9 × 10-3 钋-210 1.2 × 10-3 5.6 × 10-2 8.8 × 10-3 2.6 × 10-3 镭-226 2.8 × 10-4 5.7 × 10-3 9.6 × 10-4 8.0 × 10-4 镭-228 6.9 × 10-4 3.0 × 10-2 5.7 × 10-3 3.9 × 10-3 铀-234 4.9 × 10-5 1.7 × 10-4 1.3 × 10-4 7.4 × 10-5 铀-238 4.5 × 10-5 1.4 × 10-4 1.2 × 10-4 6.8 × 10-5 钍-228 7.2 × 10-5 3.7 × 10-3 3.7 × 10-4 1.4 × 10-4 钍-230 2.1 × 10-4 4.1 × 10-3 4.1 × 10-4 2.4 × 10-4 钍-232 2.3 × 10-4 1.6 × 10-3 4.5 × 10-4 2.9 × 10-4 钚-239/240 2.5 × 10-4 5.2 × 10-3 4.2 × 10-4 2.7 × 10-4 镅-241 2.0 × 10-4 4.7 × 10-3 3.7 × 10-4 2.2 × 10-4 a摘自WHO（2017），ICRP（2012） b适用于使用自来水制作瓶装牛奶喂养的婴儿 A.4特定情况下的指导水平 61 通常使用 GDWQ 中指导水平是合适的。指导水平可能是保守的，因为他们 假设全年以每天 2 升的速度消耗这种活度浓度的饮用水。如果需要，一个国家可 以针对特定情况来计算指导水平，例如针对特定的饮水量，或者针对可能更脆弱 的人口群体（例如儿童）。对于这些情况，需要适当的年饮水量和摄入剂量系数。 GDWQ 中的指导水平按第 9.4 节所述的公式计算： 这里： GLi =放射性核素 i 的饮用水指导水平（Bq/L） IDC =个人剂量标准（0.1 mSv/a） q =假设每年的饮水量为 730 L/y（2 L/d） h ing =成人摄入剂量系数（mSv/Bq）。 可以使用上面的公式代替当地的消费率或特定年龄的消费率（参数 q）。表 A1 中列出了儿童的默认饮水量，表 A2 中列出了 GDWQ 第 9 章（表 9.2）中列 出的常见天然和人工放射性核素对于不同年龄的摄入剂量系数。