A power plant in Charles County ranks among Maryland's top sources of toxic chemical emissions, according to new federally required reporting.

Potomac Electric Power Co. said its coal-burning Morgantown plant each year produces an estimated 5.5 million pounds of chemicals included on an Environmental Protection Agency watch list.

That amount is more than double the emissions reported by Maryland's previous top-ranked emitter of the substances, a chemical manufacturer in Baltimore.

This year is the first for utilities to join other industries in divulging their releases of the 644 chemicals on the EPA's Toxics Release Inventory. Pepco made its estimates public ahead of the July 1 deadline for reporting such emissions to the EPA.

With the new reporting, many power plants instantly will vault into top positions on lists of chemical emitters that so far have been dominated by other industries.

For instance, Baltimore Gas & Electric Co. estimates its paired Brandon Shores/Wagner power plants in northern Anne Arundel County put out 12.4 million pounds of listed chemicals annually -- more than the combined total for Maryland's previous top five emitters.

For utilities, the substances in question include acidic gases -- hydrochloric acid, hydrofluoric acid and sulfuric acid -- and metals such as manganese, barium, nickel and copper.

The chemicals exist in coal and are released when it burns.

Pepco spokeswoman Nancy Moses said the utility released the emissions estimates, which were included in a recent mailing to all customers, "so we can show we have nothing to hide."

Moses said the substances involved "are not toxic, but are labeled toxic under this reporting."

"The numbers may be high in terms of a number of substances produced by burning coal, but the health risks are low, if at all," Moses said.

Environmental advocates conceded that the emissions do not violate state and federal clean air requirements. But they said health impacts are uncertain.

"There is no reliable information," said Patricio Silva, who studies industrial emissions for the Natural Resources Defense Council, a nonprofit environmental group.

Standards for exposure to many chemicals on the Toxics Release Inventory were developed using adults in industrial settings, Silva said. He said that leaves unresolved whether children or other vulnerable populations might be harmed.

The acidic gases can irritate lungs and affect the eyes, skin and mucous membranes, Silva said. He said sulfuric acid contributes to acid rain and to over-enrichment of estuaries such as the Chesapeake Bay.

Scott Cosenza, chairman of the Wicomico Scenic River Commission, said Pepco met June 8 with his group to explain the toxics release figures.

"The accounting of this is an eye-opener," said Cosenza, whose advisory group includes members from St. Mary's County and Charles County, which share the river.

Cosenza said he anticipates no immediate action stemming from the new figures. But he said the figures would enhance his group's understanding of the Morgantown plant and its effect on the area.

The Toxics Release Inventory reporting is separate from long-standing rules concerning utilities' release of the smog- and soot-causing chemicals, nitrogen oxide and sulfur dioxide.

Last year the U.S. Public Interest Research Group, a nonprofit advocacy group, listed the Morgantown plant among the country's 100 largest emitters of nitrogen oxide and sulfur dioxide.

Moses said Pepco had spent $143 million at Morgantown since 1990 to reduce its nitrogen oxide emissions by about one-third, with further reductions planned.

She said steps to reduce the release of substances on the Toxics Release Inventory could cost as much as the plant is worth. "As long as you burn coal, they will produce significant amounts of these substances," Moses said.

In 1997, the latest year for which federal figures are available, Maryland's largest producer of listed chemicals was the Millennium Inorganic Chemicals Co. in Baltimore. It told the EPA that it released 2.6 million pounds of listed chemicals.

Pepco said its Chalk Point plant, in southern Prince George's County on the Patuxent River, produces 3.4 million pounds annually of listed chemicals.