Hair mercury

Two of the epidemiologic studies used in EPA s risk assessment—those conducted in the Faroe Islands and New Zealand (Kjellstrom et al. 1986 Kjellstrom et al. 1989 Grandjean et al. 1997)—documented a significant inverse biomarker-neurodevelopment relationship.2 Effects included poor performance on a number of tests—tests of attention, fine-motor function, language, visual-spatial abilities, and verbal memory. The magnitude of the deficits was consistent with increases in the number of children struggling to keep up in school or requiring remedial action (Rice et al. 2003). Those effects correlated with hair mercury in both studies cord blood showed the... 

Analyses of methyl mercury in scalp hair can be used to make a retrospective estimation of maternal exposure during pregnancy. It has been found that children born to mothers, whose hair mercury concentrations ranged between 70 and 640 pg Hg/ g, show a considerably higher prevalence of developmental changes than controls. Scalp hair levels exceeding 6 pg/ g are considered elevated and should be confirmed by a 24-hour urine collection. 

The overall study cohort was broken down into sub-groups based upon maternal hair mercury concentration as follows 3 ppm (n=164), 4-6 ppm (n=215), 7-9 ppm (n=161), 10-12 ppm (n=97), and >12 ppm (n=99). No significant or remarkable effect on the activity of the respective groups of children was observed outside the highest concentration group (i.e., maternal hair concentrations >12 ppm). 

Mercury can accumulate in human hair following oral exposure to mercuric chloride (Suzuki et al. 1992). Hair mercury levels, determined using segmental hair analysis, can be used to monitor exposure to mercury and may leave a historical record of exposure or uptake. In hair cut 41 days after mercuric mercury ingestion (13.8 mg/kg), a sharp peak (40 nmol/g [8 g/g]) was found in the 1 cm segment... 

Chronic Oral MRL for Methylmercury Hair levels are typically used as an index of exposure to methymercury. A number of studies report that hair mercury levels correlate with total intake levels and with organ-specific levels of mercury. Suzuki et al. (1993) analyzed 46 human autopsies in Tokyo, Japan and reported that hair mercury levels were highly significantly correlated with organ Hg levels in the cerebrum, cerebellum, heart, spleen, liver, kidney cortex, and kidney medulla, when the total mercury or methyl mercury value in the organ was compared with the hair total mercury or organic mercury, respectively. 

Nakagawa (1995) analyzed total mercury in hair samples from 365 volunteers in Tokyo, and reported higher mercury levels in those who preferred fish in their diet, compared to those who preferred other foods (preference choices were fish, fish and meat, meat, and vegetables). The mean hair mercury levels were 4 ppm in men who preferred fish and 2.7 ppm in women who preferred fish. The lowest hair mercury levels were seen in men and women who preferred vegetables, 2.27 and 1.31 ppm, respectively. The mean hair level for the whole group was 2.23 ppm (median 1.98). 

Other studies have confirmed a good correlation between hair mercury and brain mercury levels. In a study on the Seychelles Islands cohort, Cemichiari et al. (1995b) compared maternal hair levels, maternal blood levels, fetal blood levels, and fetal brain levels. Autopsy brains were obtained from infants dying from a variety of causes. The concentrations of total mercury in six major regions of the brain were highly correlated with maternal hair levels. This correlation was confirmed by a sequence of comparisons among the four measurements. Maternal hair levels correlated to maternal blood levels (r=0.82) and infant brain levels (f0.6-0.8). Concentrations in maternal blood correlated with infant blood levels (r=0.65) and infant blood levels correlated to infant brain levels (r=0.4-0.8). 

Accordingly, ATSDR used maternal hair mercury levels as the exposure measurement to derive a chronic MRL for methylmercury. While hair analysis can be confounded by outside sources of contamination (e g., as might occur in certain occupational settings) (Hac and Krechniak 1993), the study population used as the basis of the chronic oral MRL for methylmercury is far removed from external or industrial sources of mercury, effectively eliminating this as a consideration for the following analysis. 

The neurobehavioral test battery used in the 66-month Seychelles study was designed to assess multiple developmental domains (Davidson et al. 1998). The tests were considered to be sufficiently sensitive and accurate to detect neurotoxicity in the presence of a number of statistical covariates. On-site test administration reliability was assessed by an independent scorer, and mean interclass correlations for interscorer reliability were 0.96-0.97 (Davidson et al. 1998). The sample size was determined to be sufficient to detect a 5.7-point difference on any test with a mean (SD) of 100 (16) between low (0-3 ppm) and high (>12 ppm) hair mercury concentration groups for a 2-sided test (A = 0.05 at 80% power). 

Female dentists and dental assistants exposed to metallic mercury vapors had increased reproductive failures (spontaneous abortions, stillbirths, and congenital malformations) and irregular, painful, or hemorrhagic menstrual disorders (Sikorski et al. 1987). Correlations were observed between the incidence of these effects and hair mercury levels. 

As seen in other studies comparing European to Japanese hair mercury levels, the hair levels reported by Nakagawa (1995) of 2-4 ppm for a Japanese population are 10-20 times higher than levels observed in the Drasch et al. (1997) study (median, 0.247 g/g in hair range, 0.43-2.5 g/g). These differences in the mercury exposure may affect not only the mercury hair levels but also the mercury hair-to-tissue... 

Chen W, Margara J, Endoh K, et al. 1990. Comparison of hair mercury concentrations between married couples. Acta Med Biol 38(l) 45-50. 

Phelps RW, Clarkson TW, Kershaw TG, et al. 1980. Interrelationships of blood and hair mercury concentrations in a North American population exposed to methylmercury. Arch Environ Health 35 161-168. 

Suzuki T, Hongo T, Matsuo N, et al. 1992. An acute mercuric mercury poisoning Chemical speciation of hair mercury shows a peak of inorganic mercury value. Hum Exp Toxicol ll(l) 53-57. 

Experimental design. This MRL is based on the results of the Seychelles Child Development Study (SCDS), a series of evaluations on a population in the Seychelles Islands. The chronic oral MRL for methylmercury is based upon the Seychelles Child Development Study (SCDS), in which over 700 mother-infant pairs have, to date, been followed and tested from parturition through 66 months of age (Davidson et al. 1998). The SCDS was conducted as a double-blind study and used maternal hair mercury as the index of fetal exposure. Enrollees were recruited by the head nurse/hospital midwife by asking the mothers if they wished to participate in the study when they arrived at the hospital for delivery. The first 779 who did not decline participation became the mothers in the study cohort. Of the initial 779 mothers enrolled in the study at parturition, 740 remained at the predetermined child testing age of 6.5 months,... 

---