Polychlorinated biphenyls (PCBs) are a group of man-made organic chemicals consisting of carbon, hydrogen, and chlorine atoms. PCBs were domestically manufactured from 1929 until manufacturing was banned in 1979 due to their harmful effects on human and environmental health. PCBs were used in hundreds of industrial and commercial applications, including electrical equipment, thermal insulation material, adhesives, plastics, and carbonless copy paper. PCBs have no known taste or smell and range in consistency from an oil to a waxy solid. PCBs are very stable mixtures that are resistant to extreme temperature and pressure. PCBs are fairly chemically unreactive, which made them attractive for industries. PCBs are toxic and can cause harmful health effects in humans and animals. PCBs can enter the environment through spills, leaks from electrical and other equipment, and improper disposal and storage. PCBs can be found worldwide and can persist in the environment for a long time. PCBs can degrade or breakdown in the environment, but the process greatly depends on the chemical makeup of the PCBs and where they are in the environment.