EPA officials say most of the increase could be attributed to the closure of one copper plant in Arizona. Dismantling a plant results in waste that is released into the environment, rather than sent to on-site landfills.

According to the EPA, the last rise in national pollution levels came in 1997, with a six percent increase. Since that time, EPA figures show a steady decline in toxic pollution, including a 13 percent drop in 2001.

But environmental groups charged Tuesday that the EPA is underestimating the amounts of harmful chemicals being released into the atmosphere. A spokeswoman for the Washington-based Environmental Integrity Project says the EPA is lenient on its reporting on the toxic releases of refineries and chemical plants.