Sushi lovers may eat their raw tuna with or without wasabi, but one unwanted ingredient they cannot avoid is mercury. In recent tests conducted by an environmental group and a newspaper, the kind of tuna used in sushi was found to contain alarming levels of mercury. While the presence of mercury in certain kinds of fish isn't news, the lack of government warnings about the potential risks is appalling.
In one test by Oceana, tuna from a St. Petersburg restaurant contained 1.4 parts per million of mercury, which is more than three times the average level estimated by the U.S. Food and Drug Administration. The difference is significant, particularly for pregnant women, because it is thought that even small amounts of mercury can affect fetal development. In fact, the FDA advises those women to limit their intake of fish high in mercury (1 ppm) to no more than 7 ounces a week.
The New York Times conducted its own tests of tuna in sushi and found similar results. Tuna with mercury concentrations as high as 1.4 ppm was being served at sushi restaurants around Manhattan. That exceeds the "action level" at which the FDA can take food off the market, though it has rarely done so with tuna.
In recent years the FDA has proved to be a timid regulator on food safety. If the federal government cannot let people know what they are eating and the risk it carries, then the states should step in. Tuna served in restaurants or sold in grocery stores should be regularly tested for mercury and the results posted, as well as a general warning about mercury in seafood.
In the meantime, consumers will have to protect themselves. Mercury levels are highest in large predator fish, such as bluefin and yellowfin tuna (popular for sushi) and swordfish. Pregnant women and children should avoid eating those species of fish. More information is available on the Internet, at sites like environmentaldefense.org, which has a printable seafood selector.
You may still choose to eat tuna sandwiches and sushi, but at least you'll be forewarned of the risks.