At the same time, EPA officials and environmentalists note the worrisome release of persistent bioaccumulative and toxic chemicals (PBTs), which increased by 50 million pounds or 11 percent in the latest reporting year. These include dioxins, mercury, and polychlorinated biphenyls (PCBs).
"PBT chemicals are of particular concern," reports the EPA, "not only because they are toxic, but also because they remain in the environment for long periods of time and are not readily destroyed (they persist) and build up or accumulate in body tissues (they bioaccumulate)."
In 2003, for example, mercury and mercury-compound releases jumped 41 percent. Mercury is a highly toxic substance that can poison wildlife and cause brain and nervous-system damage in children and fetuses. Unlike most other pollutants, mercury tends to concentrate in dangerous "hot spots."
"Although it is good news that overall releases are back on track, it is a major concern that some of the most hazardous chemicals have increased so dramatically," says Meghan Purvis, an environmental health specialist with US Public Interest Research Group in Washington.
Meanwhile, according to the watchdog group Environmental Integrity Project, the 50 dirtiest among the nation's 359 largest power plants generate as little as 14 percent of the electric power but account for a disproportionately large share of pollution emissions: up to 50 percent of sulfur dioxide emissions, 42 percent of mercury, 40 percent of nitrogen oxides, and 35 percent of carbon dioxide.
"A huge share of these emissions comes from a handful of unnecessarily dirty power plants that have not yet installed modern pollution controls, or which operate inefficiently," says Eric Schaeffer, director of the Environmental Integrity Project and the EPA's former chief of regulatory enforcement.