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- PCBs are a family of chemical compounds which do not exist in nature but which are man-made. Commercial mixtures are clear, pale yellow liquids, manufactured by the replacement of hydrogen atoms on the biphenyl molecule by chlorine. Because of their physical properties, PCBs are commonly found in electrical equipment which requires dielectric fluid such as power transformers and capacitors, as well as in hydraulic machinery, vacuum pumps, compressors and heat-exchanger fluids. Other uses include: lubricants, fluorescent light ballasts, paints, glues, waxes, carbonless copy paper, inks including newspapers, dust-control agents for dirt roads, solvents for spreading insecticides, cutting oils. PCBs are stable compounds and although they are no longer manufactured they are extremely persistent and remain in huge quantities in the atmosphere and in landfill sites. They are not water-soluble and float on the surface of water where they are eaten by aquatic animals and so enter the food chain. PCBs are fat-soluble, and are therefore easy to take into the system, but difficult to excrete.
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| Abstract from DBPedia | Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by the Stockholm Convention on Persistent Organic Pollutants in 2001. They are organic chlorine compounds with the formula C12H10−xClx; they were once widely used in the manufacture of carbonless copy paper, as heat transfer fluids, and as dielectric and coolant fluids for electrical equipment. Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a host of problems were identified. With the discovery of PCBs' environmental toxicity, and classification as persistent organic pollutants, their production was banned by United States federal law in 1978, and by the Stockholm Convention on Persistent Organic Pollutants in 2001. The International Agency for Research on Cancer (IARC) rendered PCBs as definite carcinogens in humans. According to the U.S. Environmental Protection Agency (EPA), PCBs cause cancer in animals and are probable human carcinogens. Many rivers and buildings, including schools, parks, and other sites, are contaminated with PCBs and there has been contamination of food supplies with the substances. Moreover, because of their use as a coolant in electric transformers, PCBs still persist in built environments. Some PCBs share a structural similarity and toxic mode of action with dioxins. Other toxic effects such as endocrine disruption (notably blocking of thyroid system functioning) and neurotoxicity are known. The bromine analogues of PCBs are polybrominated biphenyls (PBBs), which have analogous applications and environmental concerns. An estimated 1.2 million tons have been produced globally. Though the federal ban was enforced by the EPA as of 1979, PCBs continued to create health problems in later years through their continued presence in soil and sediment, and from products which were made before 1979. In 1988, Tanabe estimated 370,000 tons were in the environment globally and 780,000 tons were present in products, landfills and dumps or kept in storage.ポリ塩化ビフェニル（ポリえんかビフェニル、polychlorinated biphenyl）またはポリクロロビフェニル (polychlorobiphenyl) は、ビフェニルの水素原子が塩素原子で置換された化合物の総称で、一般式 C12H(10－n)Cln (1≦n≦10) で表される。置換塩素の数によりモノクロロビフェニルからデカクロロビフェニルまでの10種類の化学式があり、置換塩素の位置によって、合計209種の異性体が存在する。 略してPCB（ピーシービー）とも呼ばれる。なお、英語ではプリント基板（printed circuit board）との混同を避け「PCBs」と呼ばれる事もある。 熱に対して安定で、電気絶縁性が高く、耐薬品性に優れている。加熱や冷却用熱媒体、変圧器やコンデンサといった電気機器の絶縁油、可塑剤、塗料、ノンカーボン紙の溶剤など、非常に幅広い分野に用いられた。 一方、生体に対する毒性が高く、脂肪組織に蓄積しやすい。発癌性があり、また皮膚・内臓への障害やホルモン異常を引き起こすことが分かっている。 (Source: http://dbpedia.org/resource/Polychlorinated_biphenyl) |
