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The Bush administration on Tuesday ordered a nearly 50 percent cut in mercury pollution (search) from power plants over the next 15 years, adopting a market-based strategy that would raise electricity prices but help protect fetuses and young children from nerve damage.

"The United States is the first nation to take a leadership role in addressing the problem of mercury from power plants," said Jeffrey Holmstead, the Environmental Protection Agency's (search) top air pollution official. EPA estimates 48 tons a year of mercury pollution from the nation's 600 coal-burning power plants will decrease to 31.3 tons in 2010, 27.9 tons in 2015 and 24.3 tons in 2020.

But even as EPA's regulations were being announced, they faced immediate political and legal opposition from senators, environmentalists and public health advocates. Opponents said EPA's approach, favored by the utility industry, fails to do all the Clean Air Act (search) requires by not making deeper cuts nationwide in harmful mercury emitted by coal-burning power plants.

"At the behest of industry, the Bush administration has just endorsed the continued poisoning of children and pregnant women with mercury," said Sen. James Jeffords, I-Vt., siding with several Democratic and Republican senators. "We will fight it in the courts, we will fight it here in Congress and we will fight it in statehouses across the nation."

Under the new mercury regulations, utilities would not be required to do anything more during the first five years than they are already required to do under another power plant rule EPA issued last week.

Those regulations, which were aimed at cutting pollution that drifts downwind across state lines, require more utilities to install scrubbers to reduce fine particles from sulfur dioxide (search) and to use chemical processes to reduce smog-forming ground-level ozone from nitrogen oxides (search). EPA officials say those changes also will help mercury emissions.

But during the second phase of the regulations, EPA will allow a "cap-and-trade" approach that sets a maximum on how much pollution should be allowed, then lets companies trade within those limits. Some companies can increase pollution while others turn a profit selling unused pollution allowances.

Dan Riedinger, spokesman for the power industry's Edison Electric Institute (search), said a cap and trade approach is preferable to setting a single deadline for making technology improvements that, once met, gives "little or no incentive" to cut more pollution.

Scott Segal, director of the Electric Reliability Coordinating Council (search), a group of power companies, said using market forces to control pollution would result in significant cuts while providing stability for consumers and electricity producers.

"The federal government is wise to avoid overly inflexible mercury control programs," Segal said. "If regulations force utilities to shift from coal to natural gas, the result is predictable" -- higher electricity prices.

Utilities could also meet the EPA's targets by switching to cleaner-burning coal or natural gas. But power plants at first will not have to do anything more than what is required to reduce two other pollutants under a rule EPA issued last week to address air pollution that travels long distances, agency spokeswoman Cynthia Bergman said.

That's because the mercury rule "relies completely" during first five years, she said, on incidental cuts from scrubbers to reduce fine particles from sulfur dioxide and from chemical processes to reduce smog-forming ground-level ozone from nitrogen oxides.

After that, power plants are expected to find ways to specifically reduce mercury.

"While this rule is protective of public health, most of the mercury that creates health risks for Americans comes from fish contaminated from sources that we can't control," Bergman said Monday. "This is a global problem."

In the meantime, she said, pregnant women and women of childbearing age should heed government warnings to limit fish intake, since most Americans consume fish from abroad.

Mercury concentrations accumulate in fish and work up the food chain, which has prompted most states to issue fish consumption advisories. Forty percent of mercury emissions come from power plants, but those emissions have never been regulated as a pollutant.