THURSDAY, April 22 (HealthDay News) -- The tuna sushi that you order in restaurants may have higher concentrations of mercury than the sushi you buy at your local supermarket, a new study finds.
Supermarkets tend to sell sushi made from yellowfin tuna, which contains less mercury than other tuna species, researchers report.
"We found that mercury levels are linked to specific species," Jacob Lowenstein, a graduate student working with the American Museum of Natural History in New York City, said in a news release from the museum. "So far, the U.S. does not require restaurants and merchants to clarify what species they are selling or trading, but species names and clearer labeling would allow consumers to exercise greater control over the level of mercury they [consume]," he added.
For their study, the researchers combined two efforts: DNA barcoding performed at the museum to identify specific species; and a mercury content analysis from experts at Rutgers University. The report was published online April 21 in Biology Letters.
"People who eat fish frequently have a particular need to know which species may be high in contaminants," said Michael Gochfeld, professor at Robert Wood Johnson Medical School in New Jersey. "Some agencies have been afraid that any mention of contaminants will discourage people from eating any fish."
The team sampled sushi from 54 restaurants and 15 supermarkets in New York, New Jersey and Colorado, and tested them for relative mercury content. Through DNA barcoding, 100 samples were identified as either bigeye tuna, yellowfin tuna or three different bluefin tuna species.
The team reported that all species tested exceeded or approached mercury concentrations permissible by the United States, the European Union, Japan and Canada, plus those set by the World Health Organization.
Higher mercury levels were found in bigeye tuna and bluefin akami, which is a lean, dark red tuna, than in bluefin toro, a fatty tuna, and yellowfin tuna akami, the researchers said. Mercury tends to accumulate in muscle rather than fat, so mercury content is usually -- but not always -- higher in leaner fish. Yellowfin tuna, for example, is lean, but may accumulate less mercury because it is smaller and harvested earlier than other species, they said.
The seafood industry took a critical view of the report.
"This is a study that tests mercury levels in fish, but stops short of any work exploring what -- if anything -- those levels mean for health," said Gavin Gibbons, director of media relations at the National Fisheries Institute, in an institute statement issued Wednesday.
He added that research has shown that "eating fish as a whole food -- omega-3s, selenium, lean protein, traces of mercury and all -- is a boost to heart and brain health."
In addition, Gibbons said, the U.S. Food and Drug Administration's mercury limit for seafood includes a 1,000 percent safety factor, "and approaching that limit or even slightly exceeding it does not equal health risk," he said.
To learn more about mercury in seafood, see the U.S. Environmental Protection Agency.
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