The U.S. Environmental Protection Agency imposed new air pollution rules on cement factories in South Carolina and elsewhere across the country, hoping to reduce mercury emissions and other harmful pollutants.

The limits announced Monday are the first of their kind for existing cement kilns, which along with coal-burning power plants are among the nation's main sources of mercury pollution.

Conservation groups long have pushed for stricter cement kiln rules, arguing that regulatory loopholes have allowed cement companies to pump massive amounts of toxins into the air.

While the cement industry has said the new rules would be a serious financial burden, the EPA estimated the rules will yield $7 to $19 in public health benefits for every dollar in costs.

Mercury can damage children's developing brains, and particle pollution is linked to asthma, irregular heartbeat, heart attacks and premature death in people with heart and lung disease.

"Americans throughout the country are suffering from the effects of pollutants in our air, especially our children who are more vulnerable to these chemicals," EPA Administrator Lisa P. Jackson said.

South Carolina has a cluster of cement kilns in the Harleyville/Holly Hill area operated by Lafarge North America, Giant Cement and Holcim. Earlier this year, Lafarge agreed to spend $170 million to cut air pollution at its Harleyville plant and 12 others around the country.

The Portland Cement Industry said five to 10 plants across the country could close because of the regulations. "Although the standards in the final rule are not quite as stringent as those originally proposed in May 2009, the emission limits are still very low and will not be achievable by some facilities," the group's president, Brian McCarthy, said in a statement.

Cement plants, which typically burn coal, are the nation's third-largest source of industrial pollution, generating 500,000 tons per year of sulfur dioxide, nitrogen oxide and carbon monoxide, the EPA says.

The plants also are among the biggest emitters of mercury, a neurotoxin known to cause birth defects, and carbon dioxide, a greenhouse gas. When implemented in 2013, the new rules should cut 16,600 pounds of mercury from entering the atmosphere.

"For years, the cement industry has gotten a free pass to pollute our air and water," said Earthjustice attorney James Pew. "Previous administrations ignored the law and turned a blind eye towards the cost of pollution on our health and environment."

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