The rules also would lead to steep cuts in emissions of other toxins, including hydrochloric acid, hydrocarbons, soot and sulfur dioxide, according to the Environmental Protection Agency.

EPA proposed the regulations under court order after environmental groups and nine states sued, accusing the agency of shirking its duty under the Clean Air Act to regulate the cement industry’s emissions.

“Mercury and other chemicals flowing into these communities are health hazards for children, pregnant mothers, local residents and workers _ people who deserve protection,” EPA Administrator Lisa Jackson said.

The rules would cover 163 kilns in 35 states. A couple dozen others, which burn hazardous waste, would be regulated separately.

Mercury is generated from raw materials such as limestone and some fuels used to heat the kilns that bake cement, a key ingredient in concrete.

For Americans, the primary exposure to mercury comes from eating contaminated fish. Airborne mercury can change into a highly toxic form after falling into waterways. The toxic metal can damage human brains and nervous systems, and is particularly dangerous for young children.

Many states warn women of childbearing age to limit fish consumption because of mercury dangers.

EPA estimated the rules would slash mercury emissions from the kilns by 81 percent to 93 percent. The agency also predicted drop-offs of greater than 90 percent in hydrochloric acid, which would be regulated for the first time, and soot.

Hydrocarbon emissions would fall by about three-quarters, the agency said. Although not covered by the rules, sulfur dioxide also could drop up to 90 percent because it would be filtered out by the same technology that controls hydrochloric acid.

The regulation also seeks stepped-up monitoring for mercury and a more accurate means of demonstrating compliance with soot limits.

The proposed rule will be published shortly and will become final a year from then unless revised. EPA will have a 60-day public comment period and a hearing if requested. Once the regulations are final, the industry would have three years to comply by taking steps such as installing pollution control devices or changing ingredients or fuels.

The Portland Cement Association, an industry group, said it would review the proposal.

The association “continues to support regulatory approaches that allow the industry to produce the cement necessary for constructing and rebuilding the nation’s infrastructure in an environmentally responsible manner,” said Andy O’Hare, vice president of regulatory affairs.

Earthjustice, an environmental law firm in Washington, D.C., filed lawsuits over more than a decade on behalf of local activist groups to get EPA to regulate mercury from cement kilns.

The agency issued standards for mercury and hydrocarbons in 2006. But they applied only to kilns built after Dec. 2, 2005, so most kilns then operating were exempt.

Earthjustice went to court again in 2007, this time joined by nine states: Michigan, New York, Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey and Pennsylvania.

“This is great news and is a promising sign that the new leadership at EPA and in the White House is serious about protecting public health and the environment,” Pew said. “We wanted to get the maximum reduction that could be had. This might not be the maximum, but it’s a big step toward it.”