Illinois' coal-fired power plants would have to substantially cut mercury pollution by 2009 under new standards approved Thursday by the Illinois Pollution Control Board.

The proposal now goes to the Legislature's bipartisan Joint Committee on Administrative Rules, which can uphold it, reject it or seek changes.

Gov. Rod Blagojevich sought the new rules to reduce harmful mercury emissions by 90 percent - a level that would go further than federal standards to tame the pollutant.

"This was a huge step forward," said Steve Frenkel, policy director for Blagojevich. "We are now just one step away from becoming the national clean-air leader when it comes to reducing power plant emissions."

Midwest Generation, the state's largest coal-fired power generator with six Illinois plants, remains opposed to the governor's proposal, said spokesman Doug McFarlan. He said the technology needed to deliver sustained 90 percent cuts in mercury emissions isn't ready yet.

Since proposing the standards in January, the state has reached agreements with Dynegy Inc. and St. Louis-based Ameren Corp. Those power generators were granted some flexibility in reaching the mercury goals in exchange for reducing other pollutants.

The agreements with Dynegy and Ameren - which were incorporated into the proposed rule - give those utilities until 2012 to reach the full mercury reductions. The power generators agreed to reduce the amount of sulfur dioxide and nitrogen oxides their plants produce.

Under the new standards, power generators would first have cut mercury emissions by an average of 90 percent across all of their power plants, and later reach the stricter reductions at individual plants.

The Pollution Control Board held two rounds of hearings and weighed 7,000 public comments and 100 exhibits before concluding Thursday that the mercury proposal "is technically feasible and economically reasonable."

Environmental groups applauded the board's unanimous decision.

"It is a very important step by the Pollution Control Board for Illinois to adopt strong mercury pollution reduction standards that will protect children's health and the environment," said Howard Learner, executive director of the Chicago-based Environmental Law and Policy Center.

Coal-fired power plants are the leading cause of mercury pollution in the Great Lakes states, Learner said, and "it's sad that it is not safe to eat the fish" caught in Illinois lakes, rivers and streams. Many are subject to an advisory urging women of child-bearing age and young children to restrict the amount of fish they eat.

Mercury is a neurological poison and affects the developing nervous system. Developing fetuses whose mothers eat mercury- tainted fish can suffer a series of health problems ranging from mental retardation to cerebral palsy to blindness.