Two Seattle cement plants puff out as much as 100 pounds of mercury each year, according to the Puget Sound Clean Air Agency and the companies.

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Cement plants, including two in South Seattle’s Duwamish area, are pumping toxic mercury into the air.

The two Seattle plants, hulking mazes of conveyor belts and smokestacks visible from the West Seattle Bridge, puff out as much as 100 pounds of mercury each year, according to the Puget Sound Clean Air Agency and the companies.

That’s just a tiny fraction of the 23,000 pounds of mercury the Environmental Protection Agency estimates comes from U.S. cement plants every year, according to a report issued Wednesday by the environmental groups Earthjustice and the Environmental Integrity Project.

It’s also far below the record-setting levels from a cement plant in Eastern Oregon. The facility in Durkee, Ore., is thought to be the biggest single industrial source of mercury in the country, emitting more than 2,500 pounds per year, according to the report.

But Eric Schaeffer, of the Integrity Project, said even small amounts of the potent poison that affects the brain are a problem, particularly in urban areas with lots of people living nearby.

“We are talking about mercury,” he said. “No amount of it is a good thing.”

Mercury from cement plants can come from the fuel, such as coal, used to fire the kilns where limestone and other minerals are baked into cement at more than 2,000 degrees Fahrenheit. It can also come from the limestone.

The new report was released as the EPA prepares to issue draft regulations for mercury from cement plants later this year. The EPA now sets limits on how much mercury can come from new or rebuilt plants — but not from existing plants such as the two in Seattle, owned by Ash Grove Cement and Lafarge North America. Environmentalists are pushing the EPA to also regulate existing plants.

It’s not clear whether mercury from the Seattle plants winds up concentrated in surrounding neighborhoods. One kind of mercury from smokestacks spreads into the atmosphere, while other kinds are more likely to come back to earth nearby.

There’s no evidence that people in the area are at additional risk, Ash Grove Cement spokesman Scott Matter wrote in an e-mail response to questions.

“Operations at Ash Grove and other facilities are closely monitored by EPA and other regulatory agencies,” he said.

State and local health and environmental agencies said they knew of no studies looking at the mercury from the Seattle cement plants. The amount of mercury coming from the plant isn’t directly monitored by agencies. They rely on annual estimates from the companies.

The Seattle cement plants have drawn complaints from neighbors upset about fumes. A 2005 proposal by Lafarge to burn tires to fuel the plant drew opposition from residents. Lafarge now is experimenting with using the tires, to see if they will meet environmental standards.

But B.J. Cummings, of the Duwamish River Cleanup Coalition, expressed frustration that government agencies haven’t tried to figure out how big a problem the mercury from the plants poses.

“We’re certain that they’re contributing,” she said.

They’re not the only source in the area. Nucor’s nearby steel mill reported emitting 68 pounds of mercury in 2006. A Nucor official said it comes from mercury switches in cars being recycled, and that the emission levels should drop as mercury switches are phased out.

The most common source of mercury exposure for people is eating fish contaminated with the toxic metal. The state Health Department in 2006 advised against children and pregnant women eating more than one meal of Puget Sound chinook per week, partly because of mercury levels.

In a news release issued Wednesday, the EPA said it was looking at its regulations of cement plants. It also touted a 45 percent overall reduction of U.S. mercury emissions since 1990.

“Reducing mercury in the environment is an EPA priority,” the news release stated.

Warren Cornwall: 206-464-2311 or