Mercury in hair as an indicator of total body burden

Mercury in hair as an indicator of total body burden H. AL-SHAHRISTANI,a K. SHIHABb& I. K. AL-HADDAD b Hair is known to concentrate mercury, and in general the concentration of mercury in hair is proportional to and many times higher than its concen- tration in the blood. The variation of the mercury concentration in human head hair was used to follow the history of poisoning in people who ingested grain treated with methylmercury. Instrumental neutron activation analysis was used for mercury determination. The initial rising slope of mercury concentration along the hair was proportional to the daily intake of methyl- mercury per kg of body weight. The ratio of the concentration of methyl- mercury in human head hair to the average body concentration was found to be about 137. By using this ratio and measuring mercury concentration in hair, the total body burden can be calculated. In the patients studied, the peak body burden ranged from 0.8 to 4.4 mg/kg in cases showing mild symptoms, from 1.5 to 6 mg/kg in cases with moderate symptoms, and from 3 to 12 mg/kg in cases with severe symptoms. The curve of the variation in mercury concen- trations along the hair was also used to calculate the biological half-life of methylmercury in man. Forty-eight cases were studied and it was found that the frequency curve (population distribution curve) was grouped into two distinct regions. In about 90% of the population the biological half-life of methylmercury was 35-100 days, and 10% showed high values of 110-120 days. When man is exposed to mercury through his diet, he usually does not show signs of intoxication unless the mercury dose is high. Different persons have different tolerances for mercury. Therefore it is essential to have a method by which body burden in intoxi- cated persons can be determined. The most toxic form of mercury is methylmercury, which has been a source of poisoning in Iraq, Japan, Sweden, and other countries. Hair is an excellent indicator of mercury intoxication. In hair the concentration of methylmercury is many times higher than the average body concentration. In Japan, Ukital reported that in the Niigata incident many patients had hair mercury concentrations as high as several hundred pg/g. The corresponding values for blood and urine were considerably lower. Tsubaki2 recorded the mercury content of hair and blood of Japanese patients at different times. He showed that the variation of mercury concentration in hair with time appeared to parallel the variation in the blood. The ratio of mercury concentration in hair to that in blood was about 500:1. In a number of studies attempts have been made to correlate the daily intake of mercury with its concentration in blood and hair. The results have been summarized by Wallace et al.3 who reported that the ratio of the average concentration of mercury in hair to that in the red blood corpuscles is about 110:1. Clarkson & Shapiro4 correlated the blood mercury concentration with the daily intake of methylmercury. They plotted mercury concentration in the red blood corpuscles against the daily intake from several sources.5 - College of Engineering, University of Baghdad, Baghdad, Iraq. - Nuclear Research Institute, Baghdad, Iraq. - 105 - 106 A straight line was obtained, with a slope of 1.4 ng of mercury per g of red blood corpuscles per pg of mercury ingested per day. Birke et al.6 calculated the methylmercury intake for 7 Swedish fish eaters. They reported that a mercury intake of 0.1 mg per day from fish would give rise to a mercury level of 80 ng per g of whole blood. The average ratio of mercury concentration in hair to that in blood was 280:1. In this study an attempt is made to correlate the mercury content in hair with the total body burden of mercury. This is partiaularly useful in calculating the total body burden of persons who have been exposed to mercury but who show no symptoms. KINETICS OF INTAKE AND EXCRETION OF METHYLMERCURY The rate of excretion of methylmercury from the body is proportional to the body burden in the species studied.4,7 The rate of increase of the body burden (dB/dt) equals the daily intake (D) minus the rate excretion. dB/dt = D -_(B where B = body burden, J = excretion rate constant, and t = time after start of intake. On integration the following equation is obtained: B = Boexp(-Xt) + (D/ )§-exp(-At2) (1) where Bo = inital body burden. This equation gives the variation of the body burden with time and its relation to the daily intake. At the onset of exposure the initial body burden is usually insignificant, and the rise in body burden is given by: B = ( /A)/ii-exp(-Xt)7 (2) At the initial stages of exposure, when t is small, B = (D/.)(At) = Dt Hence a plot of body buraen (B) versus time would have an initial rising slope of D. After prolonged exposure, when t is very large, B Dlj) where Bw = body burden at infinite time. When exposure ceases (i.e., D = 0), the fall in the body burden is given by: B = Bmexp(-)T) (3) where Bm = maximum body burden at end of exposure and T = time after end of exposure. From the last equation, the half-life of methylmercury in the body,t = ln2/\. The pro- portion of body burden that is excreted daily is: 107 -d. Bdt =A x 100% Taking the average half-life of methylmercury in man to be about 70 days, the percentage of the body burden excreted per day would be 1%. In other words the body burden at steady state is 100 times the daily intake of methylmercury in man. MERCURY CONCENTRATION PROFILE IN HAIR The change in mercury concentration in hair is parallel to the change in concentration in blood.2 Hence, assuming the hair growth rate to be constant, the variation of the mercury concentration along the hair is expected to follow the curve given by equations(2) and (3). A typical curve for the variation of mercury concentration along the hair is given in Fig. 1. At the far end, the mercury concentration is about 1.5 pg/g, which is typical for the normal background in Iraq. With the start of exposure the mercury concentration rises along the hair according to equation.2 The initial rising slope of the curve is propor- tional to daily intake. The ratio of the mercury concentration in hair to the average body concentration is given by the product of the initial slope and the hair growth rate divided by the daily intake of methylmercury per kg of body weight. FIG. 1. VARIATION OF MERCURY CONCENTRATION ALONG THE HAIR The hair growth rate can be individually determined for each patient by dividing the hair length from the point of the first rise in the slope to the end of the hair by the period between the start of ingestion and the time of sample collection. 108 The mercury hair content (C) increases from a background value according to the equation: c = (RD/Wl)fl - exp(-AP/g)7 (4) where R = ratio of mercury concentration in hair to the average concentration in the body, D = daily intake, W = body weight, A = excretion rate constant, P = hair length, and = hair growth rate. At the end of exposure, the mercury concentration in hair reaches the maximum level Cm, and thereafter the concentration drops exponentially along the length. C = Cmexp (-AC/) (5) The initial rising slope of this curve is given by R/Wg and a slope of the declining section on a semilog plot would be2V/g. From this the half-life can be calculated. The above derivations are only true for single hairs growing at a uniform rate. However, in practice it is very difficult to determine the mercury content of a single hair, and usually a bundle of hair consisting of 50-100 strands is analysed. These strands may not necessarily all have the same growth rate, and on cutting they may shift logitudinally relative to each other. These two factors would cause the point of maximum concentration in each strand to dislocate and not to match against the corresponding points on the other strands. Hence the maximum concentration measured on the bundle would be less than the true concentration as would have been obtained from a single hair. A detailed discussion of the effect of these factors on the measured values of the maximum concentration in hair, biological half-life and hair growth rate is given by Giovanoli-Jakubczak & Berg The combined effect of these factors on the experimental values of biological half-life and hair growth rate as determined by analysing bundles of hair is very small and there is usually no need for correction. The value of maximum concentration can be simply correc- ted by multiplying it by a factor. Extrapolation of the declining section of the curve to the point of peak concentration (the broken line in Fig. 1) gives a good estimate of true maximum concentration in hair. METHOD Several hundred samples of hair were collected from persons who had and who had not ingested methylmercury-treated wheat during the outbreak of 1971-72. Great care was taken to cut the samples as close as possible to the scalp. Each sample was tied firmly to ensure that there was no shifting of strands during transport. Among the cases studied were 184 patients (74 male and 110 female) who admitted that they had consumed treated grain. Of these, 143 (48 male and 95 female) showed symptoms of mercury intoxication. Forty-eight(43 female and 5 male) samples were sectioned in 1-cm lengths to study the variation of mercury concentration along the hair. Of these 48 volunteers, only 30 gave us reasonably accurate information on the total amount of wheat they had ingested and on the period of consumption. For these 30 patients the ratio of mercury concentration in hair to the average body concentration was calculated. Neutron activation analysis was used for mercury determination. The hair samples (10-100 mg) were washed in alcohol, dried, and weighed accurately. The samples were then weighed in high-purity aluminium foil containers and irradiated together with mercury standards for 20-50 hinavertical channel of the Iraqi nuclear reactor. The thermal neutron flux at the irradiation position was 3-5 x 1012n/cm2-s. After irradiation, the samples were taken under a shield to a hot cell, where they were kept for 5-7 days for the short-lived interfering activities of 24Na, 38C1, and 56Mn to decay. The samples were then counted on a high-resolution Ge(Li) detector for 200 s each. The 69 keV X-ray and 78 keV f-ray photopeaks of 197Hg were used. A sensitivity of 0.1 pg/g was obtained. 109 RESULTS The average daily intake of methylmercury by 30 patients is shown in Table 1. Estima- tion of the average daily intake is based on the average daily consumption of treated wheat for each person. Each patient was asked how many bags of treated wheat were consumed by the family, how many people were in the family, and how long the wheat lasted. Allowance was made for the lower consumption of wheat by small children and the aged. The average10 concentration of methylmercury in the treated wheat was taken as 7.9 )pg of mercury per g. TABLE 1. DAILY INTAKE OF METHYLMERCURY AND RATIO OF CONCENTRATION IN HAIR TO THE AVERAGE BODY CONCENTRATION FOR PATIENTS STUDIED Methylmercury Code Sex Age Daily intake Hair Ratio of(years) concentration hair concentration (mg) pg per kg daily increase to average body wt. (pg/g) body concentration 51 F 32 1.58 28.8 3.1 108 52 F 50 1.42 25.8 4.8 186 53 F 10 1.66 51.8 7.6 147 57 F 28 1.32 24.0 4.0 167 58 F 35 1.66 30.2 6.7 222 59 M 12 1.66 41.5 6.5 156 60 M 22 1.84 33.5 6.0 179 61 F 65 1.84 36.8 3.7 101 62 F 15 1.84 36.8 6.1 163 68 F 12 1.40 36.9 4.5 122 69 M 30 1.58 24.3 5.8 239 70 M 10 1.32 44.0 11.8 268 72 F 25 1.08 19.6 1.8 92 73 M 30 1.26 22.9 3.5 156 76 F 30 1.32 24.0 5.2 217 80 F 35 1.10 20.0 2.7 135 82 M 12 1.10 27.5 2.3 84 83 F 12 1.10 29.0 4.7 160 84 F 7 1.05 47.8 6.6 138 86 F 55 0.69 13.8 1.2 87 87 F 14 1.48 32.9 3.2 95 88 F 16 2.63 54.8 5.0 91 89 F 18 1.97 39.4 3.2 82 90 F 9 1.26 45.0 4.2 93 91 F 14 1.26 27.3 3.3 121 94 F 45 1.32 24.0 2.4 100 95 F 35 1.05 19.1 1.6 84 100 F 16 1.26 26.3 3.6 137 102 F 60 1.05 21.0 2.3 110 103 M 8 1.10 44.0 3.6 82 110 The ratio of the hair concentration to the average body concentration for the 30 patients is also shown in Table 1. The ratio ranged from 82:1 to 268:1, with an average value of 137:1. Assuming a value of 1.4 for the ratio of the red blood corpuscle con- centration in ng/g to the daily intake of 1 pg per day, as was reported by Clarkson & Shapiro,4 and taking an average value of 110:1 for the ratio of the hair content to the content in red blood corpuscles from the data summarized by Wallace et al.,3 then a value of 0.154 pg/g is obtained, corresponding to a daily intake of 1 pg of methylmercury per day. As the average biological half-life of methylmercury in man is about 70 days,8 the body burden would be 100 times the daily intake under conditions of prolonged exposure. Hence the ratio of the mercury concentration in hair to the average body concentration is about 102:1. Biological half-lives were deternmined on 48 patients. The results are discussed elsewhere.8 Briefly, the biological half-life varied from 35 to 120 days, the distribution being grouped in two regions. About 90% of the cases had a biological half-life of methylmercury of 35-100 days, with an average of 65 days; the other 10% had a rather big high value of 110-120 days. These results are summarized in Fig. 2. FIG. 2. FREQUENCY CURVE OF BIOLOGICAL HALF-LIFE OF METHYLMERCURY IN MAN 15 C10 U. 0 10 20 30 40 50 60 70 80 90 100 110 120 Biological half-life (days) ,WO 7U8L The 184 patients who admitted to the consumption of treated grain were classified into4 diagnostic categories-according to the severity of their symptoms. The average body burden of these patients was estimated either from their daily intake of treated wheat and the duration of the consumption (the 30 cases discussed earlier), or was calculated from the hair concentration, assuming a ratio of 1:137. The results of the hair analyses on these patients have been published elsewhere.11 The average body concentration in the patients in each diagnostic category is shown in Fig. 3. The peak mercury concentration in hair of the people who ingested treated grain but showed no symptoms of methylmercury intoxication ranged from a normal background value of 1 to 300 pg/g, corresponding to an average body burden of 10 pg - 2.2 mg of mercury per kg of body weight. People with mild symptoms had peak hair mercury concentrations of 120-600 pg/g, corresponding to an average body concentration of 0.8-4.4 mg of mercury per kg of body weight. Moderate symptoms - For definition of the diagnostic categories, see p. 26). 111 ere observed in people with peak mercury concentrations in hair of 200-800 ig/g, corres- onding to an average body concentration of 1.5-6 mg of mercury per kg of body weight. eople with severe symptoms, had peak hair concentrations for mercury of 400-1600 pg/g, orresponding to an average body concentration of 3-12 mg of mercury per kg of body weight. FIG. 3. SYMPTOMS OF METHYLMERCURY INTOXICATION RELATED TO THE AVERAGE BODY CONCENTRATION No Symptoms Mids,mptomsE 11110111111MI, Severe Symptoms, .I 0 2 4 6 8 10 12 WHO 75844 Average concentration of mercury in the body (mg/kg) vLSCUSSION Tejning examined 44 Swedish fish eaters and estimated their average daily intake at 44 )ig methylmercury per day. Their mercury hair content was 7.9 }ig/g. This would result in a ratio of 120:1 for the concentration in hair over the average body concentra- tion. The same ratio calculated from the data of Birke et al.6 ranges from 72:1 to 265:1, with an average value of 155:1. These estimates of the ratio of methylmercury in hair to the average body concentra- tion are lower than the values reported for our patients. Perhaps this is because in these studies, which concerned asymptomatic persons, the body burden of mercury is not purely methylmercury. Inorganic mercury is not as efficiently deposited in the hair as methyl- mercury and if it is present in the body it would lower the ratio. RESUME LA CONCENTRATION DE MERCURE DANS LES CHEVEUX EN TANT QU'INDICATEUR DE LA CHARGE CORPORELLE TOTALE On sait que le mercure se concentre dans les cheveux et que, d'une maniere generale, la concentration du mercure dans les cheveux est proportionnelle et plusieurs fois sup6rieure a sa concentration dans le sang. La variation de la concentration de mercure dans les cheveux a Xt6 utilisee pour 6tudier 1'evolution de l'intoxication chez des personnes ayant ingere des semences traitees par des compos6s methylmercuriels. On a dose le mercure par activation neutronique. Dans sa partie initiale, la courbe de con- centration du mercure dans les cheveux a presentd une pente proportionnelle a l'ingestion quotidienne de compos4s m4thylmercuriels par kg de poids corporel. On a constatd que le taux de concentration des mdthylmercuriels dans les cheveux representait environ 137 fois la concentration corporelle moyenne. La charge corporelle totale peut donc Atre calcul6e a 112 partir de ce taux. Dans le cas des malades 6tudi6s, la charge corporelle maximale variait de 0.8 a 4.4 mg/kg dans les cas pr4sentant des symptbmes lgers, de 1.5 a 6 mg/kg dans les cas presentant des symptOmes moddr6s et de 3 a 12 mg/kg dans les cas pr4sentant des symptomes graves. La courbe de variation des concentrations de mercure le long du cheveu a te 6galement utilis6e pour calculer la periode biologique des compos6s m6thylmercuriels chez l'homme. On a ftudi4 48 cas et trouv6 que la courbe de fr4quence (distribution de la population) comportait deux r4gions distinctes. Dans 90% environ de la population, la p4riode biologique des compos4s m4thylmercuriels 6tait de 35-100 jours tandis que 10% de la population presentaient des valeurs 4lev4es de 110-120 jours. REFERENCES 1. UKITA, T. Research on the mercury compounds accumulated in hairs and red blood cells. In: Proceedings of the 2nd International Symposium on Behavior of Mercury as a Component of Man's Environment, Tokyo, September 1968. Tokyo, Japan Medical Associa- tion, 1969 2. TSUBAKI, T. Clinical and epidemiological aspects of organic mercury intoxication. In: Proceedings of the Symposium on Mercury in Man's Environment, Ottawa, February 1971. Ottawa, Royal Society of Canada, 1971, pp. 131-136 3. WALLACE, R. A. ET AL. Mercury in the enviromnent. Oak Ridge National Laboratory Report ORNL NSF-EP-1, 1971 4. CLARKSON, T. W. & SHAPIRO, R. E. The absorption of mercury from food, its signifi- cance and new methods of removing mercury from the body. In: Proceedings of the Symposium on Mercury in Man's Environment, Ottawa, February 1971. Ottawa, Royal Society of Canada, 1971, pp. 124-130 5. EYL, T. B. ET AL. Mercury, fish and human health. Michigan Med., 69: 873-880 (1970) 6. BIRKE, G. ET AL. Studies on humans exposed to methylmercury through fish consumption. Arch. environ. Health, 25: 77-91 (1972) 7. ABERG, B. ET AL. Metabolism of methylmercury (203Hg) compounds in man. Arch. environ. Health, 19: 478-484 (1969) 8. AL-SHAHRISTANI, H. & SHIHAB, K. M. Variation of biological half-life of methylmercury in man. Arch. environ. Health, 28: 342-345 (1974) 9. GIOVANOLI-JAKUBCZAK, T. & BERG, G. Measurements of mercury in human hair. Arch. environ. Health, 28: 139-144 (1974) 10. BAKIR, F. ET AL. Methylmercury poisoning in Iraq. Science, 181: 230-241 (1973) 11. AL-SHAHRISTANI, H. & AL-HADDAD, I. K. Mercury content of hair from normal and poisoned persons. J. radioanalytical Chem., 15: 59-70 (1973) 12. TEJNING, S. Ziercury content of blood corpuscles, plasma, and hair in persons with a high consumption of fish from Lake Vgner7. Department of Occupational Medicine, University Hospital, Lund, Sweden. (Report No. 67-08-31, (1971))