Heavy Metal Fish

Health & Medicine 3/17/03
Heavy metal fish
New warnings about mercury tell seafood buyers to beware

By Nancy Shute
Fish is good for you. So sushi-lovers in California may be surprised by the new signs popping up in supermarkets. "Warning! Pregnant and nursing women, women who may become pregnant, and young children should not eat the following fish: swordfish, shark, king mackerel, tilefish. They should also limit their consumption of other fish, including fresh or frozen tuna."

The supermarket warnings, mandated by the state attorney general, are the latest effort to reduce the risks posed by mercury, a heavy metal that contaminates almost all seafood. New concerns about its possible role in heart disease and immune system disorders are adding to the well-known dangers of mental retardation and developmental problems in children exposed in the womb. Fish may be superb "brain food," high in protein and omega-3 fatty acids, but its benefits, we now find, may come with some perilous costs.

The alarm comes just when plans to reduce the main source of this mercury--emissions from coal-fired power plants--are being scaled back by the Bush administration. At the same time, more and more Americans are heeding the public-health message that eating fish helps combat obesity, heart disease, stroke, and other major ills. Federal agencies are further adding to the confusion by squabbling over how much mercury a person can safely eat.

"It's complicated," says Lynn Goldman, a pediatrician and professor of environmental health at the Johns Hopkins University Bloomberg School of Public Health. "With food safety you're not just talking about toxicity but about nutritional benefit."

Toxic food chain. Fish is very nutritious, and mercury is unquestionably toxic. In the 1950s, women in Minimata, Japan, exposed to high levels in fish gave birth to children with grievous birth defects. Since then, it has become clear that even low levels of mercury exposure in women can cause neurological problems in their children, affecting language, hearing, and movement. Today, the Environmental Protection Agency estimates that 8 percent of American women of childbearing age have blood mercury levels that could endanger their children. As a result, over 60,000 children are born each year at risk of lifelong problems, according to the National Academy of Sciences. Young children also can be harmed by mercury in the food they eat, because their brains are still actively developing. (The effects of childhood exposure have caused parental concerns about mercury in vaccines, too. Story, Page 44.)

Fish pick up methylmercury, a form of the element that binds to the protein in their bodies, from microorganisms in oceans and lakes. As big fish eat little fish, they absorb the methylmercury in their prey. Thus big, old fish such as swordfish, shark, and tuna carry more of the metal than salmon and shrimp. In California, consumer groups tested fish bought from seven stores, including Albertson's, Safeway, and Trader Joe's. Mercury levels in swordfish, tuna, and shark exceeded a statute's draft threshold. A lawsuit filed by the state attorney general in January prompted the new warning notices.

It's no small irony that the fish that tend to be most heavily contaminated with methylmercury are also the most expensive. After a patient suffering from hair loss was diagnosed with high methylmercury levels, Jane Hightower, a primary care physician in San Francisco, wondered if the rest of her population of doctors and dotcommers were putting themselves at risk by feasting on sushi and other gourmet fare. In a study to be published in the April Environmental Health Perspectives, she tested 89 patients and found that the majority had blood mercury levels above the Environmental Protection Agency's safety threshold of 5 micrograms per liter; one registered a whopping 89.5 micrograms. "People were ill," she says, with symptoms including fatigue, headache, memory loss, and joint aches. Mercury levels generally dropped after patients abstained from fish for six months.

But for most Americans, sushi-grade tuna is not on the menu. Canned tuna, the kind you can get for 39 cents, often is. Each year Americans eat 3.4 pounds of canned tuna per person--far more than any other fish. The Food and Drug Administration says that canned tuna usually has about half the mercury of fresh tuna. That's largely because chunk light tuna comes from smaller fish than those used for fresh fish. But in 2000, the state of Florida found that 43 percent of the canned tuna it tested would be questionable under EPA guidelines. Ten states now urge women of childbearing age to restrict consumption to one or two cans a week. (For example, see http://www.doh.wa.gov/fish/Lim itsGraph.pdf.)

Conflicting advice. Figuring what's safe is complicated, because it depends on a person's body weight, sex, and age, and also on the amount of mercury in a particular fish, which varies widely. And the government isn't helping much. The FDA allows five times as much mercury in fish as does the EPA; a 2000 report by the National Research Council backed the EPA's more conservative approach. In 2001, the FDA urged women of childbearing age and small children to avoid eating tilefish, swordfish, shark, and king mackerel (box). But the FDA has so far failed to issue guidelines on tuna and children's consumption, even though its own advisory board asked it to do so last year.

David Acheson, chief medical officer for the FDA's Center for Food Safety and Applied Nutrition, says the agency hopes to act by fall. The FDA plans to rely on public education, rather than regulation, to reduce the risk, he says. "Our whole approach to tuna and methylmercury is to make sure that the folks who need to limit their exposure get our message."

"The FDA is falling flat," says Jane Houlihan, research director of the Environmental Working Group, which is studying the health aspects of canned tuna. "Canned tuna is very important. It accounts for about half of the mercury in the public's diet." She recommends canned salmon as a cheap and nutritious, low-mercury alternative.

Researchers are only now starting to look into how methylmercury exposure may affect people through the life span. Recent studies, including one in last November's New England Journal of Medicine, suggest that men with elevated mercury levels may have more heart attacks. Animal studies indicate that low-level mercury exposure may make people more susceptible to autoimmune diseases and other immune problems.

Hightower advises her patients to quit eating grilled tuna every single day for dinner and get more variety in their diet. "We're omnivores," she says. "Eat everything, but not a whole lot of anything." She still eats sushi. "But I don't eat it very often."

Which fish is safe?

The U.S. Food and Drug Administration considers mercury levels below 1 part per million acceptable, though it warns against shark and mackerel, too. The Environmental Protection Agency has a lower threshold, about 0.2 ppm.

Fish mercury (parts per million)

Tilefish: 1.45
Swordfish: 1.00
Shark: 0.96
King mackerel: 0.73
Largemouth bass: 0.52
Tuna (fresh or frozen): 0.32
Tuna (canned): 0.17
Salmon: 0

Sources: FDA, EPA

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