Mercury and health.

ercury, particularly meth-ylmercury, is an established worldwide environmental pollutant with known toxicity in humans. The toxic effects of methylmercury in fish were first brought to light after several episodes of poisoning in Japan that involved a spectrum of adverse clinical outcomes. These ranged from par-esthesias and blurred vision to more specific signs of methylmercury intoxication , such as concentric vision and deafness, and to coma and death in some cases. Pronounced deficits in neurologic development were also noted. These outcomes were associated with the ingestion of fish that contained methylmercury at levels of 10 ppm or higher — levels clearly linked to pronounced environmental contamination and well above those normally found in fish (average level, 0.12 ppm). More recent data suggest that fe-tal exposure to methylmercury at high enough levels results in subtle decrements in several measures of neurologic development. On the basis of this concern, the National Academy of Sciences–National Research Council published a congressionally mandated report on the developmental risks of methylmercury, which led to several modifications of federal policy. The Environmental Protection Agency revised its definition of a safe level of exposure, specifying a lower level that was consistent with the report. At the same time, the Food and Drug Administration (FDA) issued a new consumer advisory on methylmer-cury and fish consumption. The most recent advisory was prompted not only by the National Academy of Sciences–National Re-PERSPECTIVE M search Council report but also by a body of evidence from large-scale prospective studies linking meth-ylmercury exposure to neurologic toxicity in humans, along with estimates of methylmercury exposure from consumption of fish. The potential risks of methylmercury in-gestion were weighed against the presumed health benefits of fish consumption. The current advisory recommends that pregnant women and women who may become pregnant avoid fish species with the highest average amounts of methylmercury: king mackerel, tilefish, shark, and swordfish. Particularly high meth-ylmercury levels are found in these species because methylmercury concentrates in species that are long-lived and are at the top of the food chain. The Table lists methylmer-cury levels in these and other key commercial species consumed in the United States. (A more comprehensive list is available from the The advice to avoid the four species with the highest methylmercury levels was extended to women who are breast-feeding and to young children. Although there is no direct evidence of a link between the consumption of contaminated fish and adverse effects …