Mercury, particularly methylmercury, 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 paresthesias 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 . . .