Tuna contains high levels of mercury, experts say

Higher priced foods usually mean healthier options but that may not be the case with tuna.

By: Jennifer Hong
Jan 30, 2008, 10:03 PM EST

Tuna favored 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 FDA shut them down and remove them from the market in consequence of mercury concentrations exceeded 1 part per million.

To scientists, the findings make sense: Mercury accumulates in a 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. Moreover, the biggest tuna—those that make the best sushi—are the biggest storehouses.

In contrast, smaller fish or even farmed tuna are probably less likely to contain high levels of contaminants, experts said. Likewise, canned tuna — currently made from lower quality meat, and smaller types of tuna—is generally less likely to be a problem.

Tuna farms now often sell fish before they become too big in part on account of rising mercury content as they grow.

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 healthier than red meat. In high doses, mercury is a neurological toxin.

However, the risks are greatest for pregnant women and nursing mothers who may pass mercury to their newborn infants.