While less than the 23,000 pounds the U.S. Environmental Protection Agency estimates cement plants nationwide release, "we are talking about mercury," Environmental Integrity Project's Eric Schaeffer told The Seattle Times. "No amount of it is a good thing."

In the report Earthjustice and the Environmental Integrity Project released Wednesday, a cement plant in Durkee, Ore., is thought to be the biggest single industrial source of mercury in the country, emitting more than 2,500 pounds a year.

Mercury discharged from cement plants can come from fuel used to fire the kilns where limestone and other minerals are baked into cement or from the limestone, the newspaper said.

The Earthjustice-Environmental Integrity Project report was released as the EPA prepared to issue draft regulations for mercury from cement plants later in 2008.

The EPA now limits how much mercury can come from new or rebuilt plants, but not from existing plants, such as the two in Seattle. State and local health and environmental agencies told the newspaper they knew of no studies on mercury from the Seattle cement plants.