The market approach has proved effective in reducing the gases that contribute to acid rain, but even some advocates of that program say it won't work with mercury. Mercury is heavier than the acid rain gases, so it tends to fall out of the air near the power plant that emits it, creating the hot spots that could be dangerous.
"Hot spots are a concern with me," said John A. Paul, a Republican environmental regulator and fisherman in Ohio who served as co-chairman of an EPA advisory committee on mercury. "I advise anyone who eats fish caught in a lake or a stream near a power plant that they are at risk, and that this rule will do nothing to protect them -- and might make things worse."
The EPA's inspector general and the Government Accountability Office, the investigative arm of Congress -- as well as numerous EPA career employees -- have criticized the mercury rule-making process as distorting or manipulating scientific analysis. EPA officials have denied those assertions.
In a prepared statement, acting EPA Administrator Steve Johnson said that nearly 80% of fish consumed by Americans comes from overseas, "from waters beyond our reach and control." EPA officials say this means that domestic reductions of mercury will have limited health benefits and that the public should follow advisories on fish consumption.
Holmstead said the U.S. was "the first nation to take a leadership role in addressing the problem of mercury from power plants." He said the government was committed to working with individual countries to reduce pollution internationally, where most of the mercury deposited in the U.S. originates.
The U.S. last month opposed a binding international treaty to reduce mercury in favor of voluntary partnerships between governments.
Studies circulated this week by one organization, Environmental Defense, said that some states -- including Colorado, Utah and Nevada -- could see significant increases in emissions, and increased local deposits of mercury, as a result of new and expanded coal-fired power plants coming online to supply California and other areas.
EPA spokeswoman Cynthia Bergman said, "We're talking in pounds, not tons. These are insignificant increases."
Holmstead said the rule's market incentives would reduce mercury enough that the agency was "quite confident" that any hot spots would be eliminated.
The EPA rule defines hot spots as mercury levels in a body of water that "are solely attributable to utility emissions."
Frank Maisano, a spokesman for the Electric Reliability Coordinating Council, a coalition of coal-fired utility companies, also said the rule's market incentives would ensure that hot spots did not occur. And states, he pointed out, still have the power to regulate mercury.
EPA officials said the cost to industry to implement the new mercury controls would reach $750 million annually by 2020.
Even as the EPA was promoting its rule, environmentalists and their allies in Congress vowed to overturn it.
"The administration has just endorsed the continued poisoning of children and pregnant women with mercury," said Sen. James M. Jeffords (I-Vt.). "We will fight it in the courts, we will fight it here in Congress, and we will fight it in statehouses across the nation."
