PCBs are mixtures of 209 different chemicals (cogeners) that come in various forms including oily liquids, solids and hard resins. PCBs are organochlorines that were manufactured until the mid-1980s, after which they were banned due to their toxicity and persistence. PCBs have been widely used as insulators in electrical equipment. They have also been used in the production of hydraulic fluids, lubricants, inks, adhesives and insecticides. They are still found in old electrical equipment and releases into the environment continue from landfills. PCBs are very persistent in the environment, taking years to degrade. They are fat-soluble and bioaccumulate in the tissues of animals. PCBs have become worldwide pollutants due to long-distance transport on air currents. Exposure to PCBs can permanently damage the nervous, reproductive and immune systems of the human body. PCBs are known carcinogens and have been linked with the development of various forms of cancer including skin and liver. In mammals, PCBs are passed via the placenta to developing young in the womb and via breast milk to newborn babies.

Mixtures of chlorinated biphenyls with different degrees of chlorination. They are quite insoluble in water and adhere readily and strongly to sediments, soils, and fatty tissue. Because they are nonflammable and have useful heat exchange and electrical insulation properties, they have been used extensively in the electrical industry in capacitors and transformers. They were also used in lubricating and cutting oil formulations as well as in pesticide formulations. Adhesives, plastics, inks, paints, and sealants. The use of PCBs, except in closed systems, has been banned in the United States since the late 1970's.