"The U.S. environmental regulator argued in court on Tuesday that its rule limiting mercury and hazardous air pollutants is 'appropriate and necessary,' not an improper interpretation of the federal Clean Air Act as industry groups and some states contend."

"The U.S. Court of Appeals for the District of Columbia Circuit, the second most powerful court in the country behind the Supreme Court, heard two cases challenging the Environmental Protection Agency's first rules to crack down on mercury from the country's fleet of electric generating units.

The EPA's Mercury and Air Toxics Standard (MATS) applies to 1,400 of the country's largest power plants and would come into force in 2015, or in some cases, 2016."

Valerie Volcovici reports for Reuters December 11, 2013. [2]