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Polychlorinated biphenyls are a group of synthetic organic compounds consisting of two interconnected benzene rings in which one or all ten hydrogen atoms are replaced by a chlorine atom. They are chemically very stable and inert, soluble in organic solvents, oils and fats. Due to their characteristics, they have been widely used as insulating and cooling materials in transformers, capacitors and refrigerators, in the manufacture of coatings, plastics, electrical transformers, etc. Health organizations have categorized them as toxic and carcinogenic.