The U.S. Environmental Protection Agency (U.S. EPA) identifies the most serious hazardous waste sites in the nation. U.S. EPA then includes these sites the National Priorities List (NPL) and targets it for federal clean-up activities. U.S. EPA has found toluene in at least 1,012 of the 1,699 current or former NPL sites. The total number of NPL sites evaluated for toluene is not known. But the possibility remains that as more sites are evaluated, the number of sites at which toluene is found may increase. This information is important; these sites may be sources of exposure, and exposure to toluene may be harmful.