revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 144
2. HEALTH EFFECTS
adverse developmental effects associated with prenatal and postnatal exposure to methylmercury in fish at
the levels experienced in this cohort. The actual exposure is reflected in a mean maternal hair level of
6.8 ppm for the prenatal exposure (SD=4.5, n=711, range, 0.5-26.7) and in a mean children’s hair level of
6.5 ppm (SD=3.3, n=708, range, 0.9-25.8) for both the prenatal and subsequent postnatal exposure. The
age-appropriate main outcome measures included: (1) the McCarthy Scales of Children’s Abilities, (2) the
Preschool Language Scale, (3) the Woodcock-Johnson Tests of Achievement—Letter and Word
Recognition, (4) Woodcock-Johnson Tests of Achievement—Applied Problems and, (5) the Bender Gestalt
test, and (6) the Child Behavior Checklist. The test results were similar to what would be expected from a
healthy, well-developing U.S. population. No test indicated a deleterious effect of methylmercury from the
exposure levels received in this population. Four of the six measures showed better scores in the highest
MeHg groups compared with lower groups for both prenatal and postnatal exposure. The authors conclude
that this result is likely due to the benefits of increased levels of fish in the diet, possibly because of
increased consumption of omega-3-fatty acids. Serum from a subset of 49 of the children was sampled for
polychlorinated biphenyl (PCB) levels. None of the samples had detectable levels (detection limit
0.2 ng/mL) for any of the 28 congeners assayed (from congener 28 to 206), indicating that was no
concurrent (i.e, potentially confounding) exposure to PCBs in this population. The median level of total
mercury for each of 25 species sampled was 0.004–0.75 ppm, with most medians in the range of
0.05–0.25 ppm, levels that are comparable to fish in the U.S. market. The authors conclude, that this most
recent NOAEL of 6.8 ppm for the SCDS cohort at 66 months of age strongly supports the findings at earlier
ages, and that the benefits of eating fish outweigh the small risk of adverse effects from an increased
exposure to methylmercury for this exposure pathway.
Weihe et al. (1996) began a long-term evaluation of the health implications for people living in the Faroe
Islands who are exposed to heavy metals and polychlorinated biphenyls (PCBs) from the consumption of
fish and pilot whales. A birth cohort of 1,000 children was examined at approximately 7 years of age for
neurobehavioral dysfunctions associated with prenatal exposure to mercury and PCB. Preliminary analyses
of the data show that several neurobehavioral tests are associated with mercury exposure parameters. With
emphasis on prenatal exposures to PCB, another cohort was generated during 1994–1995, and this cohort
will be followed closely during the next years. In the Faroe Islands, marine food constitutes a considerable
part of the diet. In addition to fish, both meat and blubber from pilot whales are included in the diet. Muscle
tissue of pilot whales caught in the Faroe Islands contains an average mercury concentration of 3.3 µg/g
(16 nmol/g), about half of which is methylmercury. In some years an evenly distributed annual catch of
pilot whales would make the average dietary intake of mercury close to more than the Provisional