Two Maryland power plants were listed among top polluters in a report issued last spring by a Washington-based environmental group.

The Chalk Point power plant just north of the Charles County line in Prince George's County was listed as the fourth-worst power plant in the nation for nitrogen air pollution, which is washed into the Chesapeake Bay and causes low-oxygen "dead zones" that suffocate marine life, according to the report by Environmental Integrity Project.

In addition, the Morgantown generating plant on the Potomac River in Charles County was cited as one of the 20 worst power plants for sulfur dioxide pollution, which causes acid rain and soot.

Subsidiaries of the Mirant Co. of Atlanta own both plants.

"What is really most outrageous about these dirtiest power plants is that most of the health effects, including asthma and heart problems, . . . are all avoidable with modern pollution controls," said Ilan Levin, counsel for the organization.

Steve Arabia, a spokesman for Mirant, said the company signed a consent decree last year requiring a 70 percent reduction in nitrogen pollution from all four of its plants in the region. Most of the improvements will be made by 2008, he said.

"There are also new federal laws in place that will require deep reductions in emissions," Arabia said. "We will comply with all of those laws and regulations, and thereby significantly reduce the emissions from our plants."

The Environmental Integrity Project was founded in March 2002 by Eric Schaeffer, a former top pollution enforcement official for the U.S. Environmental Protection Agency who resigned in February 2002 in protest of what he called the Bush administration's dismantling of air pollution regulations.

The report, called "Dirty Kilowatts," listed the 50 dirtiest U.S. power plants according to the amount of pollution they emit for each kilowatt-hour of electricity produced.

Tom Snyder, director of air pollution management for the Maryland Department of the Environment, said the Bush administration's Clean Air Interstate Rule, which uses emissions trading to encourage reductions, should cut sulfur dioxide air pollution in Maryland by 85 percent to 90 percent by 2012 and nitrogen air pollution by 60 percent to 70 percent over that period.

"It's encouraging that Mirant is already installing emissions controls," Snyder said. "The new Clean Air Interstate Rule should reduce those levels even more."

The Environmental Integrity Project says the power plant at Morgantown is one of the 20 worst U.S. power plants for sulfur dioxide pollution.