Fish Consumption Advice for Alaskans
ATSDR stated that the modifying factor of 1.5 could be removed if the results of the domain-specific tests in the 96-month Seychelles evaluation are consistent with previous results (i.e., no effects due to methylmercury exposure). As noted earlier, preliminary results of the 107-month evaluation do not support an association between prenatal exposure to low levels of methylmercury from consumption of ocean fish with background levels of contamination and adverse neurodevelopmental consequences. Thus, one may
conclude that ATSDR should raise its Minimal Risk Level from 0.3 µg/kg body weight /day to 0.4 µg/kg body weight /day.
ATSDR selected the Seychelles Islands study over the Faroe Islands study primarily because the Seychellois diet more closely resembles that of persons living in the United States. The Seychellois primary exposure to methylmercury is fish containing concentrations of methylmercury similar to the typical range seen in the United States (0.004 ppm to 0.75 ppm). The Seychellois, however, consume approximately 10 to 20 times more fish than the United States population; this is similar to the high rates of fish consumption in some Alaska communities. In contrast, the majority of methylmercury exposure in the Faroe Islands cohort was from pilot whale, with a small portion from fish. Unlike the Seychelles Islands fish, pilot whale hunted by the Faroese contains high concentrations of PCBs and organochlorine pesticides. It is still not clear to what degree concurrent in utero exposure to PCBs influenced the outcome of the neurobehavioral tests in the Faroe Islands study. 48,62,68
United States Environmental Protection Agency (EPA) In 2001, EPA calculated its reference dose of 0.1 µg/kg body weight/day for methylmercury using the results of the Faroe Islands study.60,69 Grandjean et al reported “significant associations between either maternal hair mercury or cord-blood mercury and decrements in several neuropsychological measures.”60 EPA selected the Boston Naming Test as the critical endpoint. To estimate the level of exposure or dose that is associated with an increase in adverse effects, or “benchmark dose”, EPA relied on the statistical analysis performed by Butdz-Jorgensen et al.64 The benchmark dose, defined as the dose associated with a doubling of the rate of incorrect responses on the Boston Naming Test (from 5% to 10%), was 85 ppb mercury in cord blood. Using current models and applying an uncertainty factor of 10, EPA then used the lower 95% confidence limit of the benchmark dose, i.e., 58 ppb, to calculate a reference dose of 0.1 µg/kg body weight/day, a value
identical to that derived from the Iraqi data.71 The reference dose of 0.1 µg/kg body weight/day corresponds to a hair mercury concentration of 1.2 ppm and a blood mercury concentration of 5.8 ppb.
Health Canada Health Canada has derived a provisional tolerable daily intake (PTDI) of methylmercury for women of reproductive age and infants of 0.2 µg/kg body weight/day, and they use 0.5 µg/kg body weight/day for other
adults.48 Based on the recent epidemiological data, Health Canada established a provisional No Observable Adverse Effect Level of 10 ppm mercury in maternal hair. By applying an uncertainty factor of 5 to account for interindividual variability, Health Canada derived the Provisional Tolerable Daily Intake of 0.2 µg/kg body weight/day.48 For biomonitoring studies, Health Canada applies the following ranges: a blood mercury
20 ppb is normal, 20 ppb to 100 ppb is the level of concern, and greater than
100 ppb is their action level.72,73
A blood value of 20 ppb corresponds to 5 ppm in hair.
Arctic Monitoring and Assessment Programme (AMAP) Since 1991, the international Arctic Monitoring and Assessment Programme (AMAP) has evaluated the potential human health impacts of exposures to arctic contaminants such as mercury and PCBs.73,74 Public health officials from AMAP and other arctic scientists have concluded that the nutritional and physiological health benefits of traditional arctic subsistence foods outweigh potential risks from contaminants in most areas of the Arctic, and advise local public health policy makers to encourage continued traditional food use when indicated by risk-benefit analyses. 73,74