Chemical manufacturing was the fourth largest sector releasing or transferring pollutants in North America during 2006, the Commission for Environmental Cooperation (CEC) says. The largest polluting sector, with 1.1 billion kg of releases, was the industry supporting mining and oil and natural gas extraction. Next was metal mining, with 602 million kg, and electric power generation, with 506 million kg. Chemical producers, meanwhile, released a total of 357 million kg of pollutants in 2006, according to CEC, which was established under the North American Free Trade Agreement. The commission combines data from the U.S. Toxics Release Inventory and analogous programs in Canada and Mexico to track pollution trends. CEC reports that the top five pollutants released by chemical makers in the three countries during 2006 were methanol, nitric acid and nitrate compounds, manganese and its compounds, ammonia, and ethylene. But the chemical industry data reflect only operations in the U.S. and Canada because Mexico does not require reporting for these five pollutants. The commission says reporting differences among the three countries leave gaps in the tracking of industrial pollution in North America, especially for oil and gas extraction, mining, and wastewater treatment plants.