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From an article in USA TODAY April 2002.

In September 2001, 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.

In a new study, a San Francisco physician, Dr.Jane Hightower, whose yearlong study of patients in her Bay Area practice was published Friday in Environmental Health Perspectives, 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, shark and tuna 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," said Dr. Hightower.

A Food and Drug Administration advisory committee recommended in July 2001 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.

Caroline Smith DeWaal, of the Center for Science in the Public Interest, said that people were switching to fish to improve their health 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”, said 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.

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.

Rhona Applebaum, a scientist with the National Food Processors Association said
"We do know tuna contains methylmercury, 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."

The FDA and the 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 which does not regulate commercial fish has a "reference dose" that says people can be exposed to 0.1 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”, said 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 said. "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."
Ten states warn pregnant women to limit consumption of canned tuna and other commercial seafood.

The trouble, Dr.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 Dr.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 were some with low levels with symptoms," she says. "It is unclear whether these patients were having symptoms due to direct effects of mercury or a reaction to it," she says. But, she added, 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."

Dr.Hightower said that it's not known how many people might be affected by methylmercury, and that 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" she said.

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."