Sep. 19--Contradicting a key part of the Bush administration's environmental policy, a new federal study estimates most of the mercury falling into Lake Michigan comes from smokestacks close to the shoreline.

Sixteen of the top 25 sources of mercury dropped into the lake are coal-fired power plants, according to the study by the National Oceanic and Atmospheric Administration (NOAA). Some of the toxic metal comes from as far away as Nevada and Texas, the study found, but most blows toward the lake from coal plants and factories in Illinois, Wisconsin, Michigan and Indiana.

Mercury has long been considered a problem in the Great Lakes. All of the states ringing the lakes advise anglers to limit eating fish, the chief source of exposure to a metal that can cause brain damage and learning difficulties in children and increase the risk of heart disease in adults.

While there is no question on health risks of mercury, there has been considerable debate about limiting emissions from power plants, the largest man-made source of the pollutant.

The U.S. Environmental Protection Agency announced the first- ever regulations on coal-plant emissions in March, but the plan delayed steep cuts in mercury pollution for more than a decade. Bush administration officials said one of the reasons they did not order faster and deeper cuts is that mercury from the U.S. is only a small fraction of a global problem.

"They're ignoring the science," said U.S. Rep. Mark Kirk (R- Ill.), who asked NOAA to conduct the Lake Michigan study. "Chicagoland especially has a big problem with mercury."

Kirk is scheduled to release the study at a hearing Monday in the Shedd Aquarium. In a sign of how politically charged the results are, the EPA refused a congressional subcommittee's request to sign off on the report.

The study builds on published research by NOAA scientists using computer models to trace mercury pollution in the Great Lakes to specific sources. It also mirrors findings from the EPA's own scientists, who have identified the Chicago area as a "hot spot" where relatively large amounts of mercury fall back to earth.

According to the NOAA study, coal-fired power plants in and around Chicago account for the largest amount of mercury that wafts into Lake Michigan. The largest single source is a coal plant along the lake in Kenosha.

Once mercury falls into waterways, it is converted by bacteria into a potent form called methylmercury that becomes more concentrated and dangerous as it moves up the food chain.

Infants and young children are particularly vulnerable to methylmercury because their nervous systems still are developing. Although fish are considered good sources of protein and, in some species, beneficial fatty acids, women of childbearing age, pregnant women and children as old as 15 are advised to limit how much they eat.

"We're soiling our own nest," said Cameron Davis, executive director of the Alliance for the Great Lakes. "There may be a global problem with mercury, but we've got to start addressing it at home."

Under the EPA rule, utilities will have until at least 2018 to reduce mercury emissions by 70 percent. Power plants with high emissions will be able to buy credits from cleaner plants to avoid or delay installing pollution controls.

The trading system is patterned after successful efforts to reduce sulfur dioxide, the main ingredient in acid rain.

EPA officials had considered ordering more dramatic reductions in mercury from power plants. But the administration contends that would have hurt the power industry and done little to improve public health.

Utilities say it is unclear what happens to mercury once it is released into the air and that it can travel far from its source. Meanwhile, many companies are experimenting with various methods to reduce mercury emissions.

Companies pressed to improve

"We realize mercury is a serious issue and hope to find something that we can deploy at our facilities," said Doug McFarlan, spokesman for Midwest Generation, which owns five coal plants in the Chicago area.

Kirk wants the trading of mercury credits to be limited in Illinois and other states with high emissions. Companies could sell credits under his proposal, but could not buy them from others in order to keep releasing mercury into the air.

Illinois ranks fifth in the nation in mercury emissions. Power plants and factories in Chicago and two collar counties, Lake and Will, were responsible for about a quarter of the 7,022 pounds of mercury released statewide in 2003, the latest year for which figures are available.