Higher priced foods usually mean healthier options—but that may not be the case with tuna, new studies suggest. The large wild tuna fish favoured by high-end sushi brokers for their unique taste are probably the most likely to contain high levels of mercury, experts say.
In a survey conducted by New Jersey researchers for ‘The New York Times’, laboratory tests found high concentrations of mercury in a sampling of tuna used in sushi in New York city restaurants, some so high that the US food and drug administration could legally remove them from the market because mercury concentrations exceeded 1 part per million. The survey was published this week.
To scientists, the findings make sense: Mercury accumulates in fish over the life of the animal, and is concentrated when predators eat other smaller fish. That means long-lived and predatory species, such as the blue fin tuna, are especially effective mercury banks. And the biggest tuna—those that make the best sushi—are the biggest storehouses.
“The first thing you can say is that these levels are very high," said Grimur Valdimarsson, director of the fisheries industries division at the United Nation's Food and Agriculture Organization in Rome. “But if sushi bars in New York are using big old blue fins, I guess you could expect it. The smaller tuna tends to end up in cans, the bigger tuna goes upmarket."
In contrast, smaller fish or even farmed tuna are probably less likely to have high levels of contaminants, experts said. Likewise, canned tuna—generally made from lower quality meat, and smaller types of tuna—is generally less likely to be a problem.
Valdimarsson said that tuna farms now often sell fish before they become too big in part because of rising mercury content as they grow, adding: “They are very much aware of this problem."
The health effects of mercury in tuna and other large fish are a topic of active debate in the global scientific community, and many scientists caution against an exaggerated response—noting that fish is generally healthy than red meat. In high doses, mercury is a neurological toxin. But the risks are greatest for pregnant women and nursing mothers who may pass mercury to their infants.
©2008/THE NEW YORK TIMES