Group secretly tests mercury in tuna, swordfish

Tuna and swordfish collected from some California grocery stores and sushi restaurants contained mercury levels as much as three times the threshold that authorizes federal food regulators to pull seafood from shelves, according to a study by an environmental health group.

And despite pervasive concerns about the toxic heavy metal in fish, not one of the restaurants and fewer than half of the grocery stores displayed signs warning consumers about the risks of mercury exposure, according to GotMercury.org, a public health advocacy group in San Francisco.

"They are selling food with high levels of mercury - levels the federal government says are too high for children and pregnant women to eat," said Buffy Martin Tarbox, lead author of the research. "And consumers have no idea."

But representatives of the $75 billion-a-year seafood industry say the results are misleading and potentially harmful to U.S. consumers who might shun what is widely considered part of a healthy diet. And the industry's main trade association also accuses the group of waging a public relations war against seafood in an effort to protect sea turtles that are frequently caught in fishing nets. GotMercury.org is an arm of the Turtle Island Restoration Network, an environmental advocacy group.

"They want to cut down on seafood consumption so the sea turtles don't end up as bycatch," said Gavin Gibbons, spokesman for the National Fisheries Institute, the Washington, D.C., seafood trade group. "It's detrimental to public health and it's cloaked as helping the public."

Seafood samples

In a study titled "Operation Safe Seafood: Undercover Toxic Fish Testing Results, California 2010" and released to The Chronicle, Martin Tarbox and a group of volunteers gathered 98 samples of swordfish, tuna, halibut and salmon from 41 supermarkets and sushi restaurants in the Bay Area, Santa Cruz, San Diego and Los Angeles. The specimens were tested by Micro Analytical Systems in Emeryville.

Results showed detectable levels of mercury in all of the samples - which, in itself, is not surprising, given that the metal occurs naturally and is discharged frequently in water from industrial processes such as mining and energy production.

What did surprise researchers, however, was the mercury average across the samples.

Methylmercury - the type that becomes concentrated in fish tissue - averaged 1.47 parts per million for swordfish in the GotMercury.org study, compared with the U.S. Food and Drug Administration's average mercury level of just under 1 part per million. In fresh tuna, the report found an average 0.407 parts per million versus the FDA's average 0.325 parts per million.

The highest mercury level for tuna was 2.29 parts per million in a sample from Los Angeles. The city also had the highest reading for a swordfish sample, at 3.09 parts per million. Two stores in Marin County sold swordfish with the highest recorded mercury levels in the Bay Area, the study said. Tuna samples with the highest mercury counts in the region came from two restaurants in Santa Clara and San Jose.

Starts at the bottom

Methylmercury accumulates as it moves up the food chain, starting first with the microscopic aquatic bacteria that transform mercury to toxic methylmercury. The bacteria is ingested by plankton, which is eaten by small fish, then larger fish and so on. While the FDA randomly tests a small fraction of the seafood sold in the United States, there is no requirement that all fresh seafood undergo such analysis. The catch usually goes from fishing boats to processors-wholesalers to grocery stores or restaurants.