A representative of the coal industry said the rule would "destroy jobs, raise the cost of energy, and could even make electricity less reliable" while environmental and public health groups praised the move.
Frank O'Donnell, president of the national nonprofit Clean Air Watch, called the rule "a landmark accomplishment" that would be "the signature clean-air achievement of the Obama administration."
"The dirty, soot-spewing coal plant will soon become a relic of the past - a dirty industrial dinosaur," O'Donnell said.
The rule takes on a special significance in coal-centric Pennsylvania, which has three dozen coal plants. They provide about half the region's power yet their emissions foul the air and work their way through the food chain, making the fish in some streams dangerous to eat.
Officials have estimated that half of the plants will have to make expensive upgrades. Or, if that proves financially unwise, they will have to switch fuels or shut down altogether.
Pennsylvania ranks among the top states in the nation for mercury pollution from its power plants.
Health benefits
The EPA estimates the new standard will prevent up to 530 premature deaths in Pennsylvania while creating up to $4.4 billion in health benefits in 2016, when it is in full effect.
Joseph Otis Minott, executive director of the Clean Air Council, based in Philadelphia, called the action "really important to all Philadelphians, who are downwind from these major coal-burning power plants."
The rule would prevent 90 percent of the mercury in coal burned at power plants from being emitted.
New regulations and economic forces - from low natural-gas prices to high coal prices to slow growth for electricity - "are combining to make it very difficult for older coal-fired plants to continue to operate going forward," said Douglas L. Biden, president of the Electric Power Generation Association, a Pennsylvania industry group.
