PCBs or polychlorinated biphenyls are chlorinated aromatic compounds also known as pyralenes in France. These compounds were formerly used in industry, but their production and use were gradually reduced through the 1970s before finally being banned in 1987. These compounds are classified as persistent organic pollutants since they are chemically stable and have a low rate of biodegradability. They gradually build up in the environment, particularly in reservoirs such as marine or river sediments. See our articles on these substances.