TRAVERSE CITY (AP) — A Bush administration proposal for reducing mercury emissions would give more than half of Michigan’s coal-fired electricity generation units a free pass, environmental activists said yesterday.

The Public Interest Research Group in Michigan said the “clear skies” bill pending in Congress has a loophole that would exempt from regulation 39 percent of the nation’s coal-fired power units — including 30 of the 59 units in Michigan. Together, the units pump 282 million pounds of mercury into the atmosphere each year, the group said.

“Mercury is poisonous in very small amounts,” said Kate Madigan, spokeswoman for PIRGIM. “This loophole is serious business for the millions of Michiganders who eat fish.”

The U.S. Environmental Protection Agency said in a statement that the provision criticized by PIRGIM wasn’t part of Bush’s original bill, but was inserted during congressional deliberations.

“We look forward to working with Congress to pass clear skies legislation,” the agency said.

The U.S. Senate Environment and Public Works Committee last month deadlocked 9-9 on the proposed legislation. It is designed to reduce nitrogen oxides, sulfur dioxide and mercury in the air by letting smokestack industries trade pollution rights among themselves within overall caps set by the government.

Critics say the measure would do less than existing law to reduce pollution and fails to address global warming by regulating carbon dioxide emissions.

With the bill lagging in Congress, the Environmental Protection Agency last month ordered power plants to cut mercury emissions from smokestacks by nearly half within 15 years. Environmentalists dismissed the move as inadequate.

Mercury is a toxic metal that poses a variety of health risks, including nervous system damage. It can accumulate in the bodies of fish, including some species in the Great Lakes. Forty percent of mercury emissions come from power plants.

The PIRGIM report said the “clear skies” bill would grant exemptions to power plant units that emit 30 pounds of mercury or less per year — including units contained within plants that as a whole generate more than 30 pounds annually.

Madigan said her group’s findings should prod Michigan officials to impose state-level mercury emission standards. A task force established by Gov. Jennifer Granholm was supposed to make recommendations on the matter last fall but is running late.