In a report analyzing EPA emissions data by state and plant, the Environmental Integrity Project showed that although Pennsylvania plants had done better - mercury emissions fell 34 percent between 2000 and 2008 - the state still ranked third in the nation in overall mercury emissions.

"Despite years of promises, the electric-power industry has barely made a dent in its mercury emissions this decade," EIP senior attorney Ilan Levin said. The group is based in Washington.

Four Pennsylvania plants ranked among the worst 50 for total mercury emissions, and two ranked among the worst for pounds of mercury emitted per gigawatt hour of energy produced.

New Jersey ranked 43d among states with mercury emissions.

Douglas L. Biden, president of Pennsylvania's Electric Power Generation Association, called the study "pointless and silly," given that the state's five largest plants that did not already have mercury-reduction equipment were installing it. He predicted they would reduce emissions by 88 percent to 90 percent.

"It's almost like their only purpose is to get people angry about something," Biden said of the project, a nonprofit organization that several former EPA enforcement lawyers established in 2002 to advocate for better enforcement of environmental laws.

One plant that ranked high on EIP lists - Shawville in Clearfield County, owned by RRI Energy - has had high emissions because it uses local coal, which company spokeswoman Laurie Fickman said created jobs in the area.

She also said the plant had installed the latest technology to reduce mercury emissions and would test it this year.

Jan Jarrett, president of the environmental group Citizens for Pennsylvania's Future, which has pressured officials for better regulations, said the study "clearly shows that we still have a problem with mercury pollution.

Mercury, which eventually falls into lakes and rivers and accumulates in the food chain, is a neurotoxin that causes impaired development in fetuses and children.

Several years ago, Pennsylvania instituted a requirement that would have reduced mercury from coal-fired power plants by 90 percent by 2015, Jarrett said. It was overturned in court.

Likewise, the EPA under President George W. Bush passed regulations that Biden said would have required Pennsylvania plants to reduce mercury emissions by 64 percent this year.

That, too, was struck down in court. Environmentalists said it was too weak and violated the intent of the Clean Air Act.

An EPA spokeswoman said controlling mercury emissions was a high priority for the agency. Standards for coal- and oil-fired utilities will be proposed by March 2011 and made final by November 2011, she said.

"The EPA will have to stand firm and will need to strictly follow the Clean Air Act and let the science dictate the reduction," Levin said.

A state Department of Environmental Protection spokesman, Tom Rathbun, said officials could not comment because they had not seen the report, adding that it was hardly surprising Pennsylvania plants would produce a large amount of emissions, considering that they also produce large amounts of power, exporting some of it to four nearby states and the District of Columbia.

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