Environment News Service: The top 50 most-polluting coal-burning power plants in the United States emitted 20 tons of toxic mercury into the air in 2007, finds a new report from the nonprofit Environmental Integrity Project. Of the top 10 mercury emitting power plants, all but one reported an increase as compared to 2006. Once released into the atmosphere, mercury settles in lakes and rivers, where it moves up the food chain to humans who eat contaminated fish. The Centers for Disease Control has found that …