Mercury occurs naturally in the environment, but unnatural releases by humans via industrial wastes and fossil fuels elevate mercury levels. Once in the environment, mercury can be converted by bacteria into methylmercury, a toxic form that can be highly concentrated in fish. The FDA has set an overall action level for methylmercury in seafood at 1 part per million. The agency does not routinely test for mercury in fish, relying instead on industry self-policing.

When the ABC news program 20/20 conducted its own investigation of mercury in supermarket fish, it received help from Battelle, known for its ability to measure trace-level amounts of mercury. Of 40 samples of fresh shark, swordfish, and tuna, 50 percent of the shark and over 75 percent of the swordfish failed the FDA criterion. Two of the swordfish samples had mercury levels triple the FDA limit. The tuna samples were below the FDA limit.

Standard acceptable levels for mercury in freshwater fish have not been established because freshwater species are regulated by individual states. Battelle is helping to determine a more definitive answer through the U.S. Environmental Protection Agency’s (EPA) National Fish Monitoring Study. In this four-year program, game and bottom-dwelling fish from approximately 500 lakes and reservoirs are being collected and sent to Battelle for analysis of mercury as well as arsenic. There has been a wide range of results so far.

Battelle, which developed EPA-approved speciation techniques allowing measurement of mercury in the subpart-per-trillion range and arsenic in the subpart-per-billion range, has conducted several other relevant studies. In a six-year EPA study on the Florida Everglades, Battelle analyzed mercury in water, sediment, soil, vegetation, and tissue samples to better understand how mercury changes under different environmental conditions. Additionally, in two separate studies, Battelle examined fish and hair samples to estimate risk of mercury and arsenic poisoning to Alaskan natives from fish consumption and proximity to gold dredge operations. For the government of Hong Kong, Battelle addressed potential food-web transfer of arsenic to humans through consumption of seafood.

The government’s general recommendation for the majority of Americans is yes, fish is good for you, with the majority of fish on the market falling within the FDA limit for mercury. Consumers can check with state or local governments for advisories that provide information on where elevated levels of mercury or arsenic might be a problem.

References
(To view, roll mouse over the "References" heading; to hide, click on the heading)