Radiation effects on the population of Belarus after the Chernobyl accident and the prediction of stochastic effects Jacov E. Kenigsberga, Viktor F. Minenkob & Elena E. Bug/ovac
T he acciden t at th e Chemobyl nuclear power plant caused an ex tensive rele ase of radioactivity into the enviro nme n t, and mu ch of the territory of Belarus was contaminated by radionuclid es. Th e caesium137 fallo ut was high est with in a 30-km radins aro und the reac tor. which be came the "excl usion zone ". As a result of th e accident, 23% of Belarus 's territory wa s polluted by t37Cs with a density of contam inatio n more th an 37 kBq /m 2. Because of this radioactive contamination of the en vironmen t, the population of several reg io ns was expose d to radiation after the accident and received various doses. Different conditions of dos e form ation during th e pos t-accident period enable us to ide ntify vario us time periods in the radiatio n exposure of the Belarusian population . The first invo lved the effects of radionuclides with a short half-life. That is why d oses from these radionuclides occu rre d during a relatively short period (2-3 m onths after the ac ciden t) . In the first period, one of th e primary sources of radiation exposure was iod ine- l Sl , Th e ro le of ex ternal ex posure to the short-lived radionuclides whi ch fell on th e soi l was co nsid er ably lower. The con tri bu tio ns of inhalation o f ra d ionuclides and exposure to clo uds of fallout in the total dose were sm all fo r the majority of th e Belarusian population . The second period is charac te rized by th e influen ce of the long-lived ra d io n uclid es which fell o n the soil. During this period, th e infl uence of longlived radionuclides was characterized on the whol e by the in take of 137Cs with fo o dstu ffs (m ainly m ilk produced in rad io actively-con tam inated districts ) and by ex ternal gamma-exposure from radionuclides in fallout. Most of th e stron tiu m an d plutonium fallo ut landed near the power plant, on the territory from which people were evacu ated, Because of this, thc role of these radion udides in dose formation fo r the Bel arusian population is minor. During these two periods, several catego ries in the Belarnsian populat ion re ceived d oses of radia-
a Professor, Research Institute of Radiation Medi cine , Ministry of H ealth, Minsk, Belarus. b Candidate in biological science, Research Institute of Radiation Med icine , Ministry of Heal th . Minsk, Belaru s. c Candidate in medical scie nce , Research Institute of Radiation Med icin e. Ministry of Health. Minsk, Belarus .
tion . Differen t doses and conditio ns of do se form ation make it possi ble to identity other catego ries among the exposed population : people who lived in the contamin ated territories without evacuation and rel ocatio n; evacuated people; and radiation workers or "liq u id ato rs". The r ange of th yroi d doses received and special conditions of ex posure during the first period mentioned above indicate a fourth categ ory of people who were exposed in child hood, especially to th yroid irrad iation. Because of th e radiobiological characte ristics of 1311 and its high accu mula tio n in th e thyroid, local exposure of th is gland to a relatively high dose rate occurred . Estimates of thyroid doses are based on the results o f direct dosimetric investigations carried out in May:July 1986 o n persons living in contaminated areas o f Comel, Mogilev an d Brest regio ns and in th e city of Minsk. On the basis of these results of more than 250000 direct measurem ents, dos es were re constructed fo r nearly 130 000 pe rsons, of whom 30 % were children (1). T he data analysis sh ows that the highest thyroid doses were received by inhabitants of Khoiniki district, in the Comel region, who were relocated before May 5 , 1986: th e average d ose fo r adults was 159 cGy, and fo r children an d j uven iles 310 cGy. The highest doses Were rec eived by children up to age 7, whose average dose was 469 cGy. Thyroid doses over 1000 cGy were received by nearly 20% of exposed children aged be tween 6 months and 2 years, 11% of children exposed between the ages o f 2 and 7, and 0.6 % of ad ults. Relocated inhabitants of Bragin district and nonreloc a ted inhabitants of Khoiniki, Bragin and Vetka di stricts received sligh tly smaller doses. Comparison of average thyroid doses for adults and persons age d 0-18 years shows that doses received by children and j uven iles Were 3-10 times higher th an th ose for adults. The greatest differences were noted among inhabitan ts of districts from which children were not relocated in May 1986. Becau se of the peculiar meteorol ogi cal conditions during the first days after the accident, inhabita n ts of Minsk a nd Gomel, th e largest cities in Belarus, were exposed to 131I radionuclides. Significant differences in average thyroid doses were found in all age g rou ps for the inhabitants of these cities: the average dose for Gomel ch ild ren expo sed at age s under 6 months were several times higher than for the co rrespo nd ing grou p of Minsk
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Rapp. tnmest. stsust. ssm: mond., 49 (1996 )
chi ldre n . The average d oses for ad ults fro m Com el and Min sk were 11 cCy and 1,8 cC )' accord ingly. Ana lysis o f th yroi d d o ses for th e population of Belarus as a ,v .ho le shows tha t 2.3% of chil dre n ex posed bet ween 6 mon th s an d 2 yea rs o f age an d O .O~~ % o f ad ults received d o ses higher th an 1000 cGy (2). Accordi ng to the level s o f th yroid d o ses, the gro u p m o st ex posed to th is type of ra d ia tion was the child re n . T he aggrega te d ose fo r ch ild ren of Bela rus , e xposed li p to th e age of 6 is 25% o f th e aggregate thyro id d o se fo r th e e nt ire exposed Bclarusian po p ula tio n (T able 1). D uring the sec o nd period of d ose formation , do ses resu lted from prolonged ex posu re to caes iu m , stro n tiu m a nd plu ton iu m in ad d iti on to ea rlier doses. T he h ighest d o ses were found in liq u idat o rs who wo rke d near the power pla nt in 19H6- 19H7, of who m 30 % recei ved to tal d o ses in the ra nge of 50 to 100 mSv, 47 % from 100 to 250 mS\' and 7.3 % more tha n 250 mSv (3). People who we re evac uated from the 30-km zo ne recei ved d oses co m parable with value s mentio ned above for liquidato rs. In vestiga tio n o f d o ses fo r m ore than 1300 evac uees exam ine d in Minsk clin ics durin g May:Jun e of 1986, shows th a t these d oses vari ed betwee n 1 an d 850 mS\,. T he majori ty o f th e people exa mi ned (78.5 %) rece ived doses in th e 5-50 mSv ra nge. T he d o ses for 12.4% o f t hese people exceeded 100 Ill S V and fo r 1.5 % of th e m wer e in th e 250-850 nrSv ra nge.
As fo r d o ses fo r all th e Be laru sian po pulation , it is po ssibl e to co nclude th at du ri ng 1986-} 994 inhab itants of territories with a d ensity of 1:\i Cs contam in ation betwee n 555 and 1480 kBq /m 2 p rohabl y received ave rage to ta l doses of 50-60 m S\'; for inhabit an ts of ter rito ries with a density o f 1:l'iCs conta minatio n less than 555 kBq / m 2 , the dose was 20-40 ru Sv. It sho uld be em p hasized th at th e ex ternal d oses fo r in habitan ts of co n ta minated d istrict s became visibly stable by 19HY-1990. Avera ge annual internal d oses for inhabitan ts of mo st co ntami nated d istricts d ecreased by at least 10 times as co m pared to 1YH6 and as a ru le d id no t exceed 0.2-0.;") mS\" (3) . For th e inh abitan ts o f territo ries with a d en sity of ISi Cs co nt aminatio n less th an 185 kBq /m 2, intern al e xpo su re plays a leading ro le in d ose form atio n . In co n trast, for in habita nt s o f high ly contam inat ed te rrito ries, the co ntrib u tio n of the ex terna l d o se to the to ta l dose value is grea ter. On the whole , th e values of agg regate d o ses re ceived hy the Bel arusian population d u ring th e po st-accide nt period show that external d o ses arc high er th an in ternal (Table 1). Do ses received by th e r ural populat ion were 1.3 and 1.8 tim es higher (for ex te rnal and in tern al ex pos u re acc o rd ing ly) th an th o se in the urban pop ulat ion . Nearly 60 % o f d o ses rec e ived by the rural populat ion of the Republic and nearl y 70 % ofdoses in its urhan populatio n occurred in the in habita n ts of Come! d istrict. Stro n tiu m and p lu to ni u m radi on uclid es acco un t for no more th an 5% of tota l d o ses. Evalua-
Table 1 Total radiation doses (Sv per person) for the population of Belarus, 1986·1994 Tableau 1 Doses totales de rayonnements pour la population du Belarus, 1986-1 994 (Sievert-personne) Dose Belarus - Belarus G omel regionRegion de Gomel
External dose- Dose externe rural population population rurale Urban population population urbaine Internal dose - Dose Interne rural population population rurale Urban populationpopulation urbalne Thyroid dose - D ose a lathyroide total population ensemble de la population children 0-6 years enfants de 0 a 6 ans Wld nnn statist. quart.. 4911996)
9 407 7 218
5393 4 882
3 404 1 910
1 956 1 244
4664 75 117 016
315748 80 797
li 59
~':
j
!
; , '. I·
I1
~
I
tion s of stro ntium durin g the post-accident years sho w that for inha bitanLs of the Minsk district, the average adso rbed doses to red bon e marrow were 4.5 010-' Cl' p er yea r; 5.5 010-' Cl' pe r yea r for inhabitan ts of th e Mogilev di strict (4); (5 .6-6.5) 01 0-' Cl' pe r year for inhabitants of the Gornel district in 1986-19 89; a n d 1.25 0J(~' Cl' per yea r for th e same grou p in 1990-1993 (5). It is well-known that radiatio n ex posure may cause development of different co nseque nces depe nding on levels of dose. Evaluati on of doses recei ved by the Belarusian population due to the C herno byl ac ciden t show n o evidence th at could lead to deterministic co nsequences of radiation exposure.. During health examinations of the evacuated population, no determinist ic effec ts were found, in particular, no depr ession of the blood system. Among pe ople with doses between 250 a n d 85 0 mSv there were no cas es of modificat ion in blood indi cators co nnected with such doses. According to the dos es received by certain exposed catego ries of the Belarusian populatio n. it is possible to p redict th e d e velopm ent of diffe rent stochastic co nseque nces of exposure . On the basis o f well -known risk coeffici en ts (6, 7, 8, 9) predictions of radiation consequences for different ca tegories of ex pose d persons in Belaru s were m ade (T able 2). Evaluation of the expec ted rate ofgen etic disorders fo r the fir st generati on of d escendan ts of the ex pose d popul ation shows that among these
people it is possibl e to ex pec t the development of up to 200 cases of ra d iatio n-ind uced genetic disorders.. Taking into account that the spo ntaneous rate of hereditary diseases is 36 000 to 46 000 cases p e r IOclive birth s ( 7) a n d th e birth ra te fo r Be larus was 140 000 ch ildre n per r ea r (10), th e in cr ease o f gene tic disorders due to radiatio n should not exceed 0 .1% p e r yea r. The total radiation exposure due to the Chernobyl acciden t may cause 10.9 cance r deaths per 105 persons in addition to the spon taneous ra te which acco unts for ne arly 0.09% of the current annual cance r mortality rate. Th e possib le frequ en cy of thyroid cance r cases among children exposed under the age of6 ycars is 191. 2 cas es per 10" c h ild re n fo r th e e n tire RepubIic. T he high est predicted th yroid ca ncer in ciden ce rate among children exposed in the Gomel region is 812 cases per 10r , individu als. Among th e Bclarusian liq u id ators who worked at the power plant and in 30-km zone around it in 1986-1987 , not more than 250 cases of fatal cance rs arc expec ted. Thi s is a co nserva tive estimate beca use d ata o n th e life ex pectancy of liquid ators is not available. Among the evac uees, there may be nearly 100 cases o f fata l ca nc e r. It is understandable th at the above values are low in co mparison to spontaneous levels of fatal cance r and it will be ," ery difficult to evaluate the increase of fatal cance r incid ence ca used by Chernobyl e xp osure for th e catego ries o f liquidat ors and evacuees..
Table 2 Prediction of the stochastic consequences of exposure due to the Chernobyl accident for selected categories of the Belarus population Tableau 2 Prediction des eflets stochastiques de I'exposition aux rayonnements dus a I'accident de Tchernobyl pour certaines categories de la population du B elarus Category ofexposed peopleCategorie de personnes exposees Type ofstocbasnc effectType d'effet stocnasnque Expected valueValeurattendue
Belarus population Population de Belarus
Genetic disorders Troubles genetiques F atal cancer - C ancer fatal
200 cases in first generation of descentants - 200 cas dans la premiere generation de descendants 10.9 cases per 105 persons10,9 cas pour 105 personnes 191.2 cases per 105 persons191 ,2 cas pour 105 personnes 240 cases - 240 cas
C hildren under age 6 E nfants de moins de 6 ans Liquidators, 1986-1987 Personnel charge de la remise en etat en 1986-1987 E vacuees - Personnes evacuees 60
Thyroid cancer Cancer de lathyroide Fatal cancer - C ancer fatal
Fatal cancer - Cancer fatal
120 cases- 120 cas Rapp. tttmest: sta tisf. sand. mond ., 49 (1996 )
Summary Evaluation of conditions of exposu re during the postacc ident period makes it possible to identify lWO periods in the radiation exposure of Belarus's population. As a result of our investigations we obtained data about doses for four different categories in the exposed popu lation: people who lived in the con taminated terrlfories without evacuation and relocation; evacu ated ' people; cleanup workers ("liquidators"); and people who were exposed in childhood, especially for thyroid exposure. The total doses for these catego ries in different time pe riods were analysed. Evaluation of doses received by the Belarusian popu lation due to the Chernoby l acci dent shows no evidence of doses, that could lead to the deterministic consequences of radiation exposure . For all exposed gro ups we made predictions about different types of stochastic consequences of exposure.
a differentes penod es. L'evaluatlon des doses rec ues par la popu lation bielorusse a cause de I'accident de Tchernobyl montre une abse nce de do ses susceptibles d'entralner les conseque nces deterministes de l'exposition aux rayonnements. Pour tous les groupes exposes nous avons fait des predictions sur les differents types d'elfet s stochastiques de I'exposition.
On a analyse I'ensemb le des doses pour ces categories
References/References 1. Gavrilin, J.I. e t al.l ntern'll Irradiation of the thyroid in the residents of regions contamina ted with radi on uclldes in Belaru s. Ml'dical mdiolngy. 6: 15-20 (1993) . 2. Ga" Tilin, J.l. et al. IJan icttl.ultic.-s and results of dete rm iuauou of the in ternal ra diation dose to the thvr oid for 111( ' popnlan on of contaminated regions of Ikiam" . Vn:lnik"Aml,.",ii .M,.,liri,ukirll Nnulc SS.m. 2: 3543 (1Wl) . [in Russian on ly] lklnl1Uafterthe 3 . . Kaakov , V.S. et al. RndioecobJgicalJ#ualion m C1U"fTl11bj1 luridtml. ml'rliro-bialngirol t'01LJI'(/'WN", and srinllific b a sic IIf mMJum f or rtulinlion prolt't1ion ofP"",u. M i n~k . 1991, p.5. 4. Mikhalch nlko. V.C. et al. Co ntent Cif !Iotnm tium-90 in (he
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Resume E"el des rayonnemenls sur lapopulation du Bl1larus ala suile de I'accident de Tchernobyi. etprl1diclion des e"els stochastlques L'evaluation des co nditions de I'exposition durant la parioda consecuuve a I'accident permel de relever deux periodes dans I'exposition aux rayonnements de la popu lation du Belarus. A la suite des enq uetes que nous avons effecluees, nous avons oblenu des donnees relatives aux doses pour quatre categories dilferentes de populations exposees: la po pulation qui vivait sur les territoires contarnlnes et qui n'a pas ete evacuee et reloqee ailleurs; la popu lation evacuee ; le personnel charge de la remise en elat (.I iquidateurs·); etles personnes qui ant ete exposees dans leur enfance, notamment en ce qui concerne I'exposition de la thyrolde.
body of the in ha bitan ts of Min:\l and Magilcv rc.ogio n~. l.4mvook hm"," i, lYInnui. 50: 39-41 (1991) . (in Rl l...eian onl)'} 5. Pogodin. R.I. rt at Conlm l of slronliu,,,.90 and ist1Wfw.J ,of p1ulfmirun in lh, bott ) of i,,/,abilllll/J of {'.om" rrgi on. SLirnlifi,... /Jrnrliral ll.l/J'rlS o/lh, hMllhJ1rr5m.'nlirm cif/JnJ!J I" suJlrml from Ih, 6. a.mlObyl nail/mL ~fogilev. 199-1. pp 9 1-9'1. bu/u('Jitm oftllJnutJmnrrr by ;onUingrndin.um,.lUemnmmd,u;mJ ofiM NnuolUJI Couruilon Ilndiauon l'roIn1ion nndMfflSumnn,/. NCRP Report - BO, lIcthoda, t985, p. 55.
7. Beir, V. J1rtllJh 1!«IJ o/~j.nJ " 'o lullJ lltllt"1J olwnUinK rud;aJ;01I. WiUhingl on DC. Na tio nal Anldr my Pm " 1990. B. UNS CEAR. Strurrn and f:l!m.1 of 1000;n ng llndinlimJ. I99J I~ 1 0IhI e;,,,nnl AJvmbly. wilhStit,,'ijieA'mtxn. New York. UN, 1 99~. pp 'rl!J.SO-l. 9. Rrrommn,dnli01U of'''' In/"'f nlWr,al Cmn",;uum on Radioklgitnl ProI«Iion. 1990. lnl cnlation al Ccrumlssion on Rad iologi cal Protection . Publ icatio n 60. 199 J. 10. I.azyuk. C. I. et al. Dynamics of hereditary pa shologies in Bclarus and the Ch emobyl acciden t, 71 11' CNnlO l,t arribnl: ""J;ml (upmJ. 199~. pp 167· 182.
tI
IWd hl1tJ sra list, quarr., 49 (1996)
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