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.
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.
He said that "temporary local reliability problems could arise if retirements are concentrated in a certain area and there is insufficient transmission capacity to bring generation in from other areas," but overall he said, "the lights will not go out."
But Steve Miller, president and chief executive officer of the American Coalition for Clean Coal Electricity, said that the new measure was "likely to be the most expensive rule ever imposed on coal-fueled power plants. . . . People's jobs, their family budgets, and their access to affordable electricity are at stake."
There has been much debate over the job question.
Scott Segal, director of the Electric Reliability Coordinating Council, a coalition of utilities that work on air issues, said the rule was "certainly the most extensive intervention into the power market and job market that EPA has ever attempted to implement."
The EPA, however, has estimated that manufacturing and installing the necessary pollution will provide 46,000 short-term construction jobs and 8,000 long-term utility jobs.
Power plants are the largest source for airborne mercury emissions, according to the EPA. When the mercury falls back to earth and enters waterways, it becomes methylmercury, which is more toxic and migrates up the food chain into fish that people eat. Many Pennsylvania and New Jersey waterways have "advisories" cautioning people to limit the consumption of fish caught in them because of mercury contamination.
It has been estimated that more than 600,000 women of childbearing age in the United States have unsafe blood levels of mercury, which can harm the nervous systems of unborn children and cause birth defects. In young children, it can cause developmental delays, reducing IQs.
"For decades, mercury pollution has made it unsafe to eat from the Delaware," said Adam Garber, field director with PennEnvironment. "Today, President Obama said enough is enough."
The rule also would limit emissions of other air toxics, including arsenic, acid gas, nickel, selenium, and cyanide.
"Our children's futures and their brain development will no longer be sacrificed on the altar of the power industry," said Heather Sage, vice president of Citizens for Pennsylvania's Future.
The EPA said that more than half of U.S. coal-fired power plants already have technology in place that will help them meet the new standard.
Indeed, while many industry and power company officials fought the rule, companies such as PSEG in New Jersey that have already installed costly controls, supported it. They wanted to see the playing field leveled.
The mercury measure comes atop another rule finalized in July that would reduce smokestack emissions of sulfur dioxide and nitrogen oxides in Eastern states, starting in 2012.
While Pennsylvania has not had strong mercury controls, New Jersey has. Larry Hajna, a spokesman for the state Department of Environmental Protection, said officials expected all of New Jersey's plants would be able to meet the new rule, except for one unit at the B.L. England plant in Cape May County. That plant is under an enforcement agreement to add controls, switch fuels, or shut down.
New Jersey has sought help in getting upwind plants in Pennsylvania to clean up their stacks. The EPA this year approved a New Jersey petition to force pollution reductions at a coal-fired power plant across the river in Pennsylvania.
The mercury rule has its roots in 1990 amendments to the federal Clean Air Act, which gave the EPA authority to control emissions of mercury and other hazardous emissions from major sources.
The Bush administration adopted a rule in 2005, but it was so flawed - on purpose, critics contend - that it could not survive a legal challenge.
The current rule was proposed in March.
EPA estimates that for every dollar spent to reduce pollution from power plants, the American public will see up to $9 in health benefits.
Contact staff writer Sandy Bauers at 215-854-5147, email@example.com, or @sbauers on Twitter. Visit her blog at philly.com/greenspace