Czech firms released a smaller volume of pollutants into the environment in 2012 than in 2011, but the quantity of mercury released into the air and water went up, the environmental watchdog Arnica reported on Wednesday. The main polluters are traditionally located in the industrialized regions of Moravia-Silesia, Ustí nad Labem and Central Bohemia. Power generating facilities, mainly plants operated by the state-owned power utility ČEZ continue to be the biggest sources of greenhouse gas emissions, Arnica says. On the other hand the chemical plant Spolana Neratovice tops the list of polluters in the amount of potentially carcinogenic substances released. Overall the amount of carcinogenic substances released decreased by about one fifth compared with 2011.