The state Department of Environmental Protection has appealed a Commonwealth Court ruling blocking the continued implementation of state regulations that would quickly reduce mercury emissions from coal-fired power plants.

The appeal to the Pennsylvania Supreme Court last week signals the Rendell administration's intention to pursue mercury regulations, including tighter emissions limits and monitoring, that are tougher than federal standards.

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

John Hanger, DEP acting secretary, said the state wants to keep the regulations in place to provide certainty for power plants that must invest in new and expensive controls to protect human health and the environment.

Mercury is a heavy metal and a dangerous neurotoxin that can contaminate soil and water and find its way into the food chain. It 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.

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.