Critics said the report shows the Bush administration sought to minimize the benefits of reducing mercury pollution in order to justify not requiring power plant owners to buy the most effective technology for lowering mercury emissions.
"EPA has a track record of withholding information that doesn't support their agenda, and this is the latest example," said Felice Stadler, a National Wildlife Federation policy specialist.
A separate EPA-commissioned study released in February by the Harvard Center for Risk Analysis estimated there could be $5 billion a year in public health benefits from a 62.5 percent cut in the mercury released by power plants. That study too was excluded from consideration in the new rule EPA released in March.
The report on Southeast benefits, a copy of which was obtained by The Associated Press, looked at reducing mercury concentrations in marine fish and shellfish.
It did not estimate the cost of achieving this reduction but said reducing national mercury emissions by 30 percent to 100 percent would produce Southeast benefits of between $600 million to more than $2 billion.
This report also found a mercury "hot spot" — deposits of the toxic metal stretching across 50,000 square miles in the South Atlantic, from North Carolina to South Florida.
The existence of such a large mercury concentration raises questions about public assertions by EPA officials that their new rule would prevent such hot spots.
Announcing the new regulations in March, EPA's air quality chief, Jeffrey Holmstead, said, "We don't think there will be any hot spots. We're quite confident of that."
The report said the mercury hot spot off the Atlantic coast was produced by "significant rainfall in the offshore area that washes out large amounts of mercury emitted by power plants and other sources." It said U.S. pollution is responsible for 37 percent to 68 percent of the mercury deposits there.
Jason Burnett, a policy aide to Holmstead, said Thursday his agency disagrees with that conclusion.
"The question is how much of that mercury comes from U.S. power plants, and that's the quantification that we don't believe is sufficiently understood to use in a rule-making context," he said.
Mercury concentrations accumulate in fish and go up the food chain, posing the greatest risk of nerve damage to pregnant women, women of childbearing ages and young children. EPA officials also had said mercury-contaminated fish from abroad posed the biggest threat.
Stadler said the unreleased EPA report "paints a different picture — that in certain parts of the country you have a lot of Americans eating fish caught locally."
Douglas Rae, a Boston economist and principal author of the internal report, said the EPA commissioned it two years ago.
"I think it's reasonable, but people can argue about that," he said in an interview Thursday. Rae called it "the kind of analysis that EPA staff do all the time. They don't intend them to be used in a rule-making, because there are a lot of uncertainties."
A "final" version is dated January 2004, 14 months before EPA released its mercury rule for power plants. Agency officials said that report is still being internally peer reviewed, which is why it wasn't considered for EPA's rule. The March rule ordered steps it estimated would cut mercury pollution from power plants in half by 2020, from 48 tons a year now to 24.3 tons.
Environmental and health groups said EPA could achieve quicker cleanups and fewer hot spots if it ordered the nation's 600 coal-burning power plants to install hundreds of millions of dollars in new pollution controls, under a firm deadline.
Last month, the EPA publicly estimated the annual benefits of its nationwide cleanup program at $50 million a year, compared to costs for utilities and electricity users of $750 million a year by 2020. Forty percent of all U.S. mercury pollution comes from coal-fired power plants; those releases have never before been regulated.