Polychlorinated Biphenyls (PCBs)

PCBs are a group of highly stable chlorinated aromatic hydrocarbons containing from one to ten chlorine atoms. A total of 209 different PCB compounds exist; these are normally referred to as congeners. The chemical frame of PCB molecules is formed by two phenyl rings that can rotate freely. The general chemical formula for PCBs is C12H(10-n)Cln, where n denotes the number of chlorine atoms (n=1-10). Internationally, the Ballschmiter nomenclature has prevailed, assigning a number up to 209 to each congeners. The order is decided by the number of chlorine atoms in the molecule as well as by their individual position. Such a numbering system is for example also used for polybrominated di-phenyl ethers (PBDEs).

Even though they have been banned since the early 1980’s, due to their resistance to photolytic, biological and chemical decomposition, PCBs and polychlorinated terphenyls are still ubiquitous. They accumulate in the food chain and can cause significant health- and environmental problems. In case of fire or incomplete incineration, polychlorinated biphenyls and polychlorinated terphenyls can form toxic chlorinated dibenzofuranes. PCBs belong to the group of „Persistent Organic Pollutants“ (POPs) that are classified as especially dangerous industrial chemicals by the United Nations Environment Programme (UNEP). PCB production, use and import were banned in Japan in 1972. The United States Congress banned PCB production in 1979, and in the Federal Republic of Germany, PCBs have not been produced since 1983.

Literature

Stockholm Convention on Persistant Organic Pollutants