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  • A polychlorinated biphenyl is a synthetic organic chemical compound of chlorine attached to biphenyl, which is a molecule composed of two benzene rings. There are 209 configurations of organochlorides with 1 to 10 chlorine atoms. The chemical formula for a PCB is C₁₂H₁₀₋ₓClₓ. 130 of the different PCB arrangements and orientations are used commercially. Polychlorinated biphenyls were widely used as dielectric and coolant fluids, for example in electrical apparatus, cutting fluids for machining operations, carbon paper and in heat transfer fluids. Due to PCBs' environmental toxicity and classification as a persistent organic pollutant, PCB production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001. According to the U.S. Environmental Protection Agency, PCBs cause cancer in animals and are probable human carcinogens. Concerns about the toxicity of PCBs are largely based on compounds within this group that share a structural similarity and toxic mode of action with dioxin. Toxic effects such as endocrine disruption and neurotoxicity are also associated with other compounds within the group.