How safe is what's in this can?

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Pollution in our seafood
Every day in this country, coal-fired power plants in 46 states spew out particles laced with mercury. Incinerators and chlorine plants burn off still more. The emissions travel on the wind — sometimes hundreds of miles — then fall back to Earth, usually in rain or snow, and land most often in our rivers, lakes and oceans. Though there are natural sources of mercury in the air, such as forest fires, a 2002 study published in "Environmental Science & Technology" estimated that 70 percent of the mercury in our atmosphere was put there by humans.

As it turns out, bacteria in marine soil and sediment like to dine on mercury, which they convert to a toxic form called methylmercury. The bacteria are absorbed by plankton, which fish dine on. Little fish are light eaters, so they don’t consume enough mercury through plankton to become dangerous. But eventually, big fish eat the small fish, and it’s these predators that have the most mercury in their flesh. According to government data, top-of-the-food-chain fish such as shark, swordfish, tilefish and king mackerel contain 0.7 to 1.4 mcg per gram of mercury — anywhere from 8 to 100 times as much as seafood like cod, herring, clams, salmon and scallops.

And then there’s tuna. It has become a focus of mercury worries because we eat so much of it: Canned tuna is the most popular fish in the United States and the second most popular seafood after shrimp, generating close to $1.5 billion in sales annually. That means, as Dr. Hightower notes, “the issue of mercury in fish involves not only the health of the consumer, but the health of the economy.”

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As a large predator fish, tuna contains mercury — and sometimes lots of it. Government data shows that the freshly caught bigeye and ahi tuna used for steaks and sushi has levels around 0.6 mcg per gram, and albacore used to make “white” canned tuna has moderately high levels of about 0.35 mcg per gram. Light canned tuna has long been thought to have low mercury because it’s mostly made from skipjack, a smaller species. But independent laboratory testing of light canned tuna has produced wildly varying levels of mercury even among cans bought in the same store — with some light canned tuna testing higher than tuna steaks.

From the plant to your plate
How toxic mercury gets into our water, our seafood and our body.
1. Man-made menace. Mercury is a liquid metal found in rocks, including coal. When power plants burn coal, they release mercury, causing nearly half of U.S. man-made mercury pollution, according to the EPA. Power plant mercury emissions are highest in Illinois, Indiana, Ohio, Pennsylvania and Texas.
2. Nature’s pollution. Forest fires, volcanoes and other natural events can also emit the element into our atmosphere.
3. Carried away. The element may land near its source or float on the wind and clouds, even traveling to and from other countries.
4. Back to Earth. Mercury typically falls through rain or snow and lands in water. There, microorganisms munch on it and convert it into a toxic form know as methylmercury.
5. Into our nets. Plankton absorbs the organisms, then is eaten by fish. In the end, large predator fish absorb the most mercury.
The task of protecting Americans from mercury in commercially sold fish falls to the U.S. Food and Drug Administration. In its most recent advice to consumers, the FDA recommends that women of childbearing age consume up to 12 ounces — two servings — of fish or shellfish per week. It also says these women should not eat more than 6 ounces of albacore tuna per week. The FDA’s assistant commissioner for food safety, David Acheson, M.D., insists the agency has done a good job warning women about the dangers without frightening them. After all, tuna and many other types of fish are rich in vitamin B and omega-3 fatty acids that prevent heart disease. Eating fish can lower the risk for stroke, depression and mental decline. There are species, including salmon, sole, trout and flounder, that are both high in omega-3s and low in mercury. But Dr. Acheson says that if the FDA issued too dire a warning about tuna, women might turn away from fish altogether and toward fattier, less healthy sources of protein such as red meat.

The tuna industry takes the same position. “We strongly encourage women to follow the advice of the FDA: to eat seafood, including canned tuna, twice per week. They have brought in health professionals from around the nation in a very open and transparent process,” says John Connelly, president of the National Fisheries Institute in McLean, Virginia. This year, the NFI merged with the U.S. Tuna Foundation, a trade group representing the three largest brands of canned tuna. “Large, peer-reviewed, published studies (have found) that without question the best thing young women and families can do is get more seafood into their diet,” Connelly adds.