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Polyklooribifeiinit, commonly known as PCBs, are a group of man-made organic chemicals that were widely used in industrial applications until their production was banned in many countries. They consist of two benzene rings joined by a carbon-carbon bond, with chlorine atoms attached to the rings. The number and position of these chlorine atoms determine the specific PCB congener.

PCBs possess excellent electrical insulating properties, high resistance to heat and fire, and low reactivity, making them desirable for use in electrical equipment such as transformers and capacitors, as well as in hydraulic fluids, plasticizers, and carbonless copy paper. However, their persistence in the environment, resistance to degradation, and potential toxicity raised significant concerns.

Exposure to PCBs can occur through inhalation, ingestion, or skin contact. In humans, potential health effects associated with long-term exposure include skin rashes, liver damage, immune system suppression, and developmental problems. PCBs are also considered probable human carcinogens. Due to their widespread use and persistence, PCBs are found in soil, water, air, and the fatty tissues of animals, including humans, leading to bioaccumulation and biomagnification in food chains.

Regulatory efforts have focused on phasing out PCB production and use, as well as managing existing PCB-containing equipment and remediating contaminated sites. International agreements, such as the Stockholm Convention on Persistent Organic Pollutants, aim to eliminate or restrict the production and use of PCBs globally.