The state has indicated it will appeal last week's Commonwealth Court ruling that threw out a Pennsylvania rule requiring coal-fired power plants to quickly and significantly reduce mercury emissions.

Commonwealth Court Judge Dan Pellegrini ruled Friday that the rule is unlawful, invalid and unenforceable, but the state Department of Environmental Protection has received legal approval from the state Office of General Counsel to file an appeal.

"We're going to appeal it. The expectation is we will," said Teresa Candori, a DEP spokeswoman.

Pennsylvania's mercury rule was developed in 2006 after the U.S. Environmental Protection Agency proposed weakening federal mercury regulations. It requires the state's 34 coal-fired power plants to reduce mercury emissions 80 percent by 2010 and 90 percent by 2015 from 1999 emissions levels. It also prohibits mercury emissions "trading" that would allow older power plants to avoid installing expensive control equipment.

"Pennsylvania's mercury rule is the most effective and timely way to reduce mercury exposure," said Acting DEP Secretary John Hanger. "The ruling makes Pennsylvania's economy less competitive in the long run."

The federal rule, which itself was thrown out by the U.S. Court of Appeals for the D.C. Circuit last February, allowed the trading of mercury emissions credits and would have reduced mercury emissions 70 percent by 2018.

The Pennsylvania rule was challenged by Allentown-based PPL Corp., which has several coal-fired power plants in the state. The company argued that Pennsylvania cannot enforce its mercury rule because it is based on the federal mercury rule that was overturned last year.

The DEP said last week that it had already approved a number of applications for installation of mercury controls at coal-fired power plants, as well as monitoring plans for those facilities. The Commonwealth Court ruling puts those permit approvals on hold and "further puts the public health and the environment at risk," the DEP said.

Mercury is a dangerous neurotoxin that can harm pregnant women, babies and children, who are primarily exposed by eating fish. High level exposure can cause attention and language deficits, memory loss, autism, mental retardation and impaired vision and motor functions.

Because of high mercury levels in the state's fish, the state has advised limiting fish consumption from all lakes, streams and rivers.

Coal-fired power plants are responsible for about 48 tons or one-third of the nation's mercury emissions. The 71 electricity generating units at Pennsylvania's 34 coal-burning plants send about 5 tons of mercury into the air each year.

First Published: February 3, 2009, 1:00 p.m.