Methylmercury in fish: a review of residue levels, fish consumption and regulatory action in the United States.

The dangers associated with the consumption of large amounts of methylmercury in fish are well recognized, and there is some evidence to suggest that methylmercury may be the cause of subtle neurological impairments when ingested at even low to moderate levels, particularly the prenatal and early childhood periods. This concern has prompted a continuing assessment of the risk of methylmercury toxicity among fish consumers in the United States as well as other countries. The toxicokinetics of methylmercury in humans are reviewed and used to estimate body burdens associated with toxic effects. To determine seafood consumption patterns among the continental U.S. population the Food and Drug Administration (FDA) has analyzed data from a diary study commissioned by the Tuna Research Foundation. Mercury residue levels in domestic fish sampled by the FDA were used to determine the level of exposure to methylmercury. Until evidence is presented that substantially lowers the known body burden of methylmercury which causes toxicity, calculations indicate that the current 1.0 ppm regulatory level provides adequate protection for the average fish consumer, for young children, and for a significant number of consumers exceeding the acceptable daily intake. However, additional studies are being carried out in a continuing process to ensure that safe levels of prenatal exposure to mercury residues in fish are maintained.