In large doses, this causes mercury poisoning, which affects the nervous system. And mercury contamination isn't a possibility remote from the average Minnesotan's everyday life. Under some conditions, breaking these devices can result in very high exposure to mercury vapor. Mercury accumulates in aquatic species Mercury vapor can also end up in an organic compound, methylmercury, a major contaminant of Minnesota fish. Mercury in emissions from coal-fired power plants and vapors from other sources can be carried long distances in the air before it falls to Earth.
Bacteria convert some of the mercury that falls on wetlands, lakes and rivers to methylmercury.
The zooplankton, in turn, are eaten by other aquatic animals. At each level of the food chain, the concentration of methylmercury at least trebles. If a pregnant woman eats a lot of methylmercury-contaminated fish, her fetus may be damaged. A National Research Council committee recently estimated that about 60,000 children may be born in the nation each year with neurological problems that could lead to poor school performance because of exposure to methylmercury in the womb. Since the flesh of large, predatory fish, such as walleye and pike, is likely to contain high levels of methylmercury, the Minnesota Department of Health, working with the Minnesota Department of Natural Resources , has issued fish-consumption advisories for many lakes.