Mercury in Tuna Sushi Higher at Restaurants than Groceries
Tuna sushi from your local supermarket might have lower mercury levels and so be safer to eat than sushi from a high-end restaurant, a new study using fish DNA suggests.
The results show that some species of tuna, particularly those that restaurants value for their firmer flesh and appealing look — such as bluefin akami and all bigeye tuna — have higher mercury levels than other species typically found in grocery stores.
Overall, however, all the tuna had pretty high mercury levels. The levels were, on average, greater than the concentrations considered safe to consume in one day by the U.S. Environmental Protection Agency and higher than the concentrations allowed in Japan.
The research could lead to better labeling to help tuna eaters cut down on the amount of mercury they consume, something that can have toxic effects, the researchers say.
"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 imbibe," said study researcher Jacob Lowenstein, a graduate student affiliated with the American Museum of Natural History in New York, which conducted the genetic part of the research.
While previous studies have identified a difference in mercury levels between tuna species, those studies weren't necessarily reliable because they didn't have a fool-proof way of determining which tuna came from which species, said study researcher Joanna Burger, a professor at Rutgers University.
The new study used a technique called DNA barcoding to identify which tuna came from which species. With this method, scientists use a specific DNA sequence from an organism — called a species "fingerprint" — to match a sample of unknown origin with a certain species. This comes in handy for identifying tuna species, since distributors and supermarkets don't often know exactly what type of tuna they're selling, Burger said.
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