These profiles cover hazardous substances developed from a priority list of 275 substances found at National Priorities List sites. These substances are ranked based on the frequency of occurrence at NPL sites, toxicity, and potential for human exposure. Agency for Toxic Substance and Disease Registry (ATSDR) also prepares toxicological profiles for DOD and DOE on substances related to federal sites. Arranged alphabetically by common name of substance. The web site listed also has a significant number of other resources in safety, including emergency response guidelines, standards for measuring health effects of exposure, hazardous waste site listings, environmental health education, and various registries.