Mercury pollution from paper mills, power plants, and garbage incinerators can wind up in rivers and oceans, where it accumulates in the tissue of fish. That's why the U.S. government has recommended for years that people in highly polluted areas--particularly pregnant or nursing women--not eat certain fish to avoid potential neurological damage and increased risk of heart attacks. New research suggests the mercury compounds that build up in fish may not be so bad after all, but not everyone agrees.
Mercury can combine with many nonmetallic elements to form compounds that range from deadly to nearly benign. Most researchers assumed the mercury that builds up in fish is methylmercury chloride, but no one knew for sure because the levels in fish were too low to study with traditional x-ray imaging techniques. Biophysicist Graham George of the University of Saskatchewan in Saskatoon, Canada, and his colleagues used a new high-intensity x-ray beam at the Stanford Synchrotron Radiation Laboratory in California to analyze the mercury in the muscle tissue of swordfish and orange roughy bought at a local seafood market. They found that the mercury in both fish is bound to a carbon atom and a sulfur atom and is most likely methylmercury cysteine, not methylmercury chloride.
This could be good news for consumers, because methylmercury cysteine may not be as adept at crossing cell membranes as the chloride form is, and so may be less toxic, says George. Methylmercury cysteine was less toxic to day-old zebrafish larvae, the authors report in the 29 August issue of Science. "There's reason for cautious optimism that mercury in fish may not be as much of a concern as we thought," says George, although he acknowledges more work needs to be done to understand how toxic methylmercury cysteine is in people.
Other scientists praise the technical merit of the work but say it's premature--and irresponsible--to conclude that methylmercury compounds in fish don't pose a threat to human health. Studies from around the world have shown that mercury from fish can sicken or even kill people, adds Katherine Mahaffey of the Environmental Protection Agency's Office of Prevention, Pesticides, and Toxic Substances in Washington, D.C.
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