How much is safe?
The amount of canned tuna that is safe to eat each week should be based on a person's body weight according to Washington state's department of health.

Source: Fish Facts for Good Health, publication of the Washington Department of Health

Study finds elevated consumption can lead to high intake of mercury

By Anita Manning
USA Today, Nov. 5, 2002

Health-conscious Americans have been told repeatedly that fish is good for the heart and the waistline. But there is growing concern that some seafood lovers are consuming high doses of mercury along with their fish dishes and could be suffering health problems as a result.

Women of childbearing age have long been warned to limit their fish intake to reduce the risk of exposing an unborn baby to mercury. But in a new study, a San Francisco physician says she discovered high levels of toxic mercury, called methylmercury, in blood and hair samples taken from dozens of her patients -- men, women and children.

Many were suffering symptoms associated with low-level mercury poisoning, including hair loss, fatigue, depression, difficulty concentrating and headaches. The implication, she says, is that anyone who consumes a lot of fish, especially large steak fish such as swordfish and shark, could be at risk.

"You have people who have been told to eat fish because it's healthful, but they have not been told it contains contaminants," says physician Jane Hightower, whose yearlong study of patients in her Bay Area practice was published Friday in Environmental Health Perspectives, an online journal of the National Institute of Environmental Health Services, part of the National Institutes of Health.

Concern is widespread:

A Food and Drug Administration advisory committee recommended in July that the agency do research to assess the risks to women and young children who eat canned tuna. The amount of methylmercury per can is generally low, about 0.17 parts per million, but it can vary widely, says Michael Bender of the Mercury Policy Project, an advocacy group.

"Tuna is the most consumed fish in the country," Bender says. "If you're a pregnant woman and you eat over two cans of tuna per week, you can go over" safe levels of mercury. The FDA currently recommends that women who are or could become pregnant limit all fish to 12 ounces a week.

A survey of Hong Kong high school students found that as many as 10% eat enough fish to exceed safety limits for mercury exposure. The report, which prompted a Chinese government warning about consumption of shark and other large fish, found that the students' diets gave them a mercury exposure of 6.41 micrograms per kilogram (2.2 pounds) of body weight a week. The World Health Organization recommends a 5-microgram limit.

In September, the United Nations Environment Programme hosted a meeting in Geneva about ways to reduce mercury emissions around the world. A report from that meeting will be considered by environment ministers at a meeting of UNEP's governing council in February and could lead to consideration of an international treaty on mercury emissions.

Hightower's study and similar reports from other researchers who attended a recent meeting in Vermont, sponsored by the EPA, suggest that consumers who eat expensive fish are increasingly putting themselves at risk for mercury poisoning.

"They are switching to fish to improve their health," says Caroline Smith DeWaal of the Center for Science in the Public Interest, but "they're being exposed to dangerously high levels of methylmercury." That's especially troubling if the consumers are women who plan to have children, says DeWaal, author of the recently published Is Our Food Safe? "It is critical that women of childbearing age stop eating this fish from six months to a year before becoming pregnant."

The Centers for Disease Control and Prevention estimates about 8% of women in this age group have enough mercury in their bodies to pose a risk of having babies with mild learning problems.

No set standards

Mercury released from power plants, municipal waste facilities and medical incinerators is the primary source of methylmercury in fish. Methylmercury is an organic form of mercury that is different from what is in mercury thermometers or what goes up smokestacks when coal is burned.

Mercury is converted to methylmercury by bacteria in water. So when people are talking about mercury in fish, they are really talking about the toxic methylmercury. What makes it dangerous to health is that it is hard for the body to eliminate, so it can build up and may affect the nervous system. Most human exposure to methylmercury is through fish consumption.

The FDA ceased its large methylmercury sampling program in 1998, and today federal agencies conduct only limited testing of fish for methylmercury. The industry does, too, on a voluntary basis, says Rhona Applebaum, a scientist with the National Food Processors Association. "Whether it's mercury or any other defect, chemical or microbial, the industry does regular testing" to assure that the product meets FDA standards.

"We do know tuna contains methylmercury," she says, but mercury is "naturally occurring, so on a daily basis people are exposed. It's not at levels that will result in acute toxicity unless people are not practicing basic tenets of nutrition: balance, variety and moderation."

Studies show women ages 15-44 eat canned tuna 1.5 times a month, well within the range of safety, but too much of anything can be harmful, she says. "If people are going to consume one type of food literally ad nauseam, there's going to be an impact."

The FDA and Environmental Protection Agency differ on what they consider acceptable levels and measure it differently. The FDA, which regulates commercially caught fish, sets an "action level" of 1 part per million. If higher levels are reported, the FDA can remove the fish from the market, though critics say that rarely occurs. The EPA has a "reference dose" that says people can be exposed to .1 microgram per kilogram of body weight per day, which is roughly 5 to 7 micrograms per day for someone who weighs 100 to 154 pounds, says Kate Mahaffey of the EPA. That's about a fifth of the amount the FDA considers safe.

The FDA's standard permits about 480 micrograms of methylmercury in one pound of fish, she says. "If fish is that contaminated, and you're trying to keep in the 5 to 7 micrograms per day range, you can't eat much of that fish."

But the EPA does not regulate commercial fish. It works with state environmental and health departments to test local rivers and other bodies of water where recreational fishing is done and where mercury levels may be high because of local pollution. When high levels of mercury are detected in the water, the states post fish advisories to warn consumers.

"There are fish advisories in most states for mercury," says Michael Gochfeld, professor of environmental medicine at the Robert Wood Johnson Medical School in Piscataway, N.J.

Even in areas where industrial pollution has been reduced, the problem persists because of atmospheric pollution drifting from other areas, he says. "Virtually all our mercury-polluting industry in New Jersey is closed," he says, but state health officials regularly warn residents not to eat fish from specific lakes and rivers where mercury levels are high. Ten states also warn pregnant women to limit consumption of canned tuna and other commercial seafood.

Yet health experts point out that fish is an important part of a balanced diet. It's full of vitamins and other nutrients, including omega-3 fatty acids, which help lower cholesterol and blood pressure and reduce the risk of cardiac arrest. And it's low in calories.

How that squares with mercury poisoning is "a very difficult message to convey," says epidemiologist Tom Sinks of the National Center for Environmental Health, part of the CDC. "Fish is a vehicle by which people are exposed to mercury. But at the same time, fish is a good source of protein and nutrients, an important part of the diet, and one we want people to eat in a healthy way."

He says the fish that are high in omega-3, such as salmon and sardines, are low on the mercury scale. "We want to encourage people not to avoid fish, but to advise them that some fish have higher levels of mercury, and if they're concerned, they should avoid those fish," he says.

The trouble, Hightower says, is that some people appear to be more sensitive to methylmercury than others. The EPA and the National Academy of Sciences recommend keeping mercury levels in blood at 5 micrograms per liter or less. In Hightower's study, patients' blood levels ranged from 2 to nearly 90 micrograms per liter. Symptoms varied widely and did not always correlate with the burden of methylmercury.

"There were some with elevated levels who had no symptoms. There are some with low levels with symptoms," she says. "It is unclear whether these patients are having symptoms due to direct effects of mercury or a reaction to it," she says. But, she adds, most people can withstand a bee sting, while others go into shock. "We recognize there are severe reactions to very minuscule quantities of certain agents."

Hightower says it's not known how many people might be affected by methylmercury, and she can't prove that the symptoms her patients suffered were caused by overconsumption of fish, but "the funny thing is, people got better when they stopped eating it."

Not eating fish helped

That's what happened to Wendy Moro, 40, a marketing consultant who lives with her husband and son in a suburb of San Francisco. Until April 2001, she says, she was the picture of health. A 110- pound bundle of energy, she ran several miles a day, danced ballet, lifted weights. She also ate fish two to five times a week, at home and at the Bay Area's better restaurants.

"On the West Coast, we eat a lot of fish," she says. "It's an affluent community, and fish is accessible and popular. You go out for dinner. People don't go out for T-bone steaks anymore. It's all fish."

She ate tuna for lunch a couple of times a week, and the family would have seafood for dinner regularly, often choosing steak fish such as ahi tuna or halibut. "We just looked for what was fresh," she says. "I thought I was being really healthy, not eating meat, eating lots of fish."

The first sign of trouble was severe fatigue -- "the kind where it is impossible to stay awake for more than a few hours at a time," she says. Then pain and weakness in her limbs worsened to the point where she could barely stand. A series of doctors diagnosed or tested her for multiple sclerosis, muscular dystrophy, chronic fatigue syndrome, mononucleosis, diabetes insipidus. One suggested she be evaluated for mental illness.

Finally, she was referred to Hightower, who tested her for mercury poisoning. Moro's blood level was 17, more than three times the recommended level, though still below what some doctors think is enough to cause such severe symptoms.

When Moro stopped eating fish, her symptoms began to disappear. Now, she says, she's "about 85%" back to normal. She keeps a file on mercury that she gives to friends who are thinking about having a baby.

If it could happen to her, it could happen to anyone, she says. "I'm such an average Jane. I live in a suburb; I have 1.5 kids, if you count my dog. I'm not a super-fanatic, not a triathlete. I'm not super-rich or poor. I'm just an average Joe-USA TODAY. That's what's scary."

Alan Stern, chief of the New Jersey Department of Environmental Protection who served on a National Academy of Sciences committee on methylmercury two years ago, says it's too soon to draw firm conclusions from Hightower's study. "I would consider it to be the very early stages of a clinical case description, and it's not at a point yet where it can be translated into a public health message," he says.

Such reports, he says, "call our attention to the potential of health effects at low levels of exposure (to methylmercury), but they don't make an open-and-shut case."

Even the relief of symptoms reported by people who stop eating fish is inconclusive, he says, because it is "hard to distinguish that from a placebo effect. From an objective standpoint, one cannot say this association goes to the next step of cause and effect."

But if nothing else, Stern says, consumers and doctors should be alert to the possibility that small exposures to mercury in fish might cause symptoms. His cautionary conclusion: "Individuals should choose their diets wisely."

What fish should you eat?
Fish that may have high levels of mercury:	Fish that generally have low levels of mercury:
Swordfish Shark Tilefish King mackerel Tuna (steak)	Salmon Flounder Cod Catfish Trout	Pollock Clams Shrimp Scallops Lobster
Source: Fish facts for Good Health, publication of the Washington Department of Health

How mercury contamination spreads

1. The most common sources of mercury in air are coal-burning power plants, municipal waste combustors, medical waste incinerators and hazardous waste combustors.
2. Tiny particles or mercury travel through smokestacks into the air. They then fall onto soil or water.
3. Mercury can accumulate in fish and wildlife. Small fish are eaten by big fish, so big fish and fish-eating birds generally have higher levels of contamination.
4. Mercury can contaminate water or land through the discharge of industrial wastewaters.

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