Toxic air pollutants are poisonous substances that can cause cancer, birth defects, nervous system damage, and other serious health problems. They are emitted by cars, buses, trucks and a variety of industrial sources including electric power plants. Toxic air pollutants include metals, other small particles, and gases. One example is the chemical benzene, which is in gasoline. Inhaling fumes that contain benzene could increase your risk of getting cancer.

When Congress passed the Clean Air Act Amendments of 1990, it directed the U.S. Environmental Protection Agency to take action against 188 toxic air contaminants linked to cancer and other serious health problems. In addition to benzene, examples include mercury, dioxin, asbestos, cadmium, toluene and chromium. EPA already has issued standards for more than two dozen toxic pollutants. The standards eventually will reduce toxic air emissions by a million tons per year, according to the EPA.

One of the most prominent toxic problems is mercury, which accumulates in fish. Fish consumption advisories have been issued for thousands of water bodies nationwide in dozens of states. One of the biggest mercury polluters -- the electric power industry -- persuaded Congress in 1998 to forbid EPA from taking action against power plant mercury pending further study.