Tuna is the top fish on American consumers' plates and a favorite of children. But some imported canned tuna may contain far higher levels of toxic mercury than federal warnings indicate, a new study shows.
Among 144 cans of mostly foreign brand "light tuna" pulled off grocery store shelves nationwide and tested, the average mercury content was .269 parts per million (p.p.m), more than twice the average reported by the US Food and Drug Administration and far above the FDA's cutoff for fish deemed "low-mercury," the study found.
While mercury in fish isn't new, the study released Tuesday challenges the notion that "light tuna" represents little risk. "Despite the general view that light tuna contains less mercury than white albacore tuna, our results showed that mercury levels in chunk light tuna, depending on its origin, can be as high as and, in some cases far higher than, those in albacore tuna," said the study by Defenders of Wildlife, an environmental group, and the Center for Science in the Public Interest and the Mercury Policy Project, nonprofit public interest organizations.
An industry spokesman for the US Tuna Foundation, which represents US producers, declined comment, saying he needed more time to review the study. But in a December 2005 response to a Chicago Tribune series on mercury in canned tuna, the foundation said "research in the US and abroad confirms that no one is at risk from the minute amounts of mercury in this popular food."
In 2004, the Environmental Protection Agency (EPA) and the FDA issued guidelines on mercury intake from tuna, especially for children and pregnant women. Among canned tuna, "albacore" averaged higher levels of mercury while light tuna was a "low-mercury fish," the FDA said.
While federal testing has focused on US brands, mercury in imports from Costa Rica, Ecuador, Malaysia, Mexico, the Philippines, and other countries has gone largely unrecognized, says the study.
Imports are now more than half of all canned tuna sold. And some tested cans from Latin America contained more mercury than king mackerel, shark, and swordfish, considered by FDA to have the "highest levels of mercury." Ecuador, in 2003 the second-largest exporter of canned tuna to the US after Thailand, had the highest average mercury – 0.75 p.p.m., the study found. By comparison, the FDA has recommended against eating king mackerel, a fish found to have average mercury of 0.73 p.p.m.
The study recommends a thorough assessment of mercury in canned tuna, closer examination of imports, and revised FDA guidelines. It also raises questions about federal programs for low-income women and infants that often promote tuna as a low-cost source of protein.
"What we've found is that the government is not enforcing its own standards and very high-mercury containing fish is sold all the time in the US," says Caroline Smith DeWaal, of the Center for Science in the Public Interest.
An EPA spokesman deferred comment to the FDA. "We can't comment on other studies because we can't validate their test methods," FDA spokesman Michael Herndon says in an e-mail. "FDA has done extensive testing of its own and continues to stand by the  advisory."