PCBs, or polychlorinated biphenyls, are a group of man-made chemicals consisting of 209 individual compounds of a similar chemical structure. They were domestically manufactured from 1929 until manufacturing was banned in 1979 due to evidence of accumulation in the environment and harmful health effects. PCBs were used in hundreds of industrial and commercial applications, including:

• Electrical equipment like capacitors and transformers
• Hydraulic fluids, heat transfer fluids, and lubricants
• Plasticizers in paints, plastics, and rubber products
• Pigments, dyes, and carbonless copy paper
• Other industrial applications

PCBs are very stable mixtures that are resistant to extreme temperature and pressure. They do not burn easily and are good insulating material. Although no longer commercially produced in the United States, PCBs may still be present in products and materials produced before the 1979 PCB ban. PCBs can enter the environment through spills, leaks from electrical and other equipment, and improper disposal and storage. They can be found worldwide and have been detected in people and animals around the world. PCBs can affect human health, and exposure can occur through consuming PCB-contaminated fish, meat, or dairy products.