Dear EarthTalk: I know that large fish contain a lot of mercury, but where does it come from?

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Dear EarthTalk: I know that large fish contain a lot of mercury, but where does it come from? And what are we doing to prevent this contamination?--Alison Bronner, Atlanta, GA

Mercury in the fish we like to eat is a big problem in the United States and increasingly around the world. Mercury itself is a naturally occurring element that is present throughout the environment and in plants and animals. But human industrial activity (such as coal-fired electricity generation, smelting and the incineration of waste) ratchets up the amount of airborne mercury which eventually finds its way into lakes, rivers and the ocean, where it is gobbled up by unsuspecting fish and other marine life.

Once this mercury gets into the marine food chain, it "bioaccumulates" in the larger predators. That's why larger fish are generally riskier to eat than smaller ones. Those of us who eat too much mercury-laden fish can suffer from a range of health maladies including reproductive troubles and nervous system disorders. The U.S. Environmental Protection Agency (EPA) reports that human fetuses exposed to mercury before birth "may be at an increased risk of poor performance on neurobehavioral tasks, such as those measuring attention, fine motor function, language skills, visual-spatial abilities and verbal memory." Up to 10 percent of American women of childbearing age carry enough mercury in their bloodstreams to put their developing children at increased risk for developmental problems.

In partnership with the U.S. Food and Drug Administration, the EPA issues determinations periodically in regard to how much mercury is safe for consumers to ingest from eating fish. State and tribal environmental authorities and/or health departments issue fish consumption advisories for water bodies in their respective jurisdictions based on federal guidelines. The EPA consolidates these local and regional advisories on its website, where concerned consumers and...

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