One-fifth of women of childbearing age have mercury levels in their hair that exceed federal health standards, according to interim results of a nationwide survey being conducted by researchers at the University of North Carolina at Asheville.

The study, which was commissioned by the environmental advocacy group Greenpeace, offers the latest evidence of how much mercury Americans are absorbing by eating fish. Coal-fired power plants and other sources release mercury into the air, which ends up in water and is absorbed by fish. The pollutant, which is a neurotoxin that can cause developmental problems in fetuses and young children, makes its way into the bloodstream when people eat contaminated fish.

Researchers at UNC's Environmental Quality Institute based their findings on hair samples from nearly 1,500 people, many of whom learned of the study through the Internet. Participants either paid $25 to submit hair samples with a home testing kit or got free tests at 27 hair salons across the country sponsored by Greenpeace, Aveda salons and state and local environmental groups.

Study participants were not randomly chosen, but the report's author, Richard Maas, said they were evenly distributed geographically and that he believes the results reflect overall mercury contamination levels among Americans. He said the tests showed a correlation between how much fish people ate and their mercury levels: One-third of people who ate canned tuna four or more times a week, for example, had mercury levels above Environmental Protection Agency recommendations.

"There is no other pollutant out there that has anywhere near this high a percentage of the U.S. population with exposure levels above the government's health advisory levels," said Maas, co-director of the Environmental Quality Institute. "Not lead, not arsenic, nothing."

The last major national study of Americans' mercury exposure, conducted by the Centers for Disease Control and Prevention in 1999 and 2000, concluded that about 12 percent of women of childbearing age had mercury levels that exceeded EPA's safety standard.

The new study found excess mercury levels in 21 percent of the 597 women of childbearing age who were tested.

The UNC researchers said they could not explain why their subjects had higher mercury levels, as 80 percent of study participants said they had no reason to think they had high concentrations of mercury in their blood. Men and women in the study had similar mercury levels.

Greenpeace officials said the survey, which will have drawn on at least 5,000 hair samples when it is completed in March, will be used to lobby for stricter curbs on mercury pollution from power plants. The EPA is drafting rules that officials predict will cut power plant emissions by 70 percent after 2018.

Greenpeace energy campaigner Casey Harrell said that Bush's proposal is too weak, and that the government should require plants to reduce mercury pollution by 90 percent "as soon as possible."

"People should not have to stop eating fish because they're afraid they'll get poisoned by mercury," Harrell said.

EPA spokeswoman Cynthia Bergman and Frank Maisano, a utilities lobbyist, said the administration's proposal would address the problem of mercury pollution.

Bergman, who called the Greenpeace study helpful, said, "We are addressing this shared concern on all fronts -- making sure consumers, particularly pregnant women or women who may become pregnant, have clear guidance about the benefits and risks of fish consumption -- as well as attacking the problem at its source -- regulating mercury emissions from power plants for the very first time. Mercury is a serious health risk."

This spring, EPA and the Food and Drug Administration recommended that young children, nursing mothers, pregnant women and women who may become pregnant should not eat more than two servings, or 12 ounces, of fish per week. David Acheson, chief medical officer at FDA's Center for Food Safety and Applied Nutrition, said women would have to "be quite a bit above" the government's recommended safety level before they or their children would be at risk.