PCBs và PBBs là hóa chất công nghiệp không xảy ra tự nhiên trong môi trường. Các tài sản, sử dụng và chất độc của PCBs được mô tả chi tiết trong Safe (1984) và EHC 140; PBBs được mô tả trong Safe (1984) và EHC 152. PCBs lần đầu tiên được sản xuất thương mại khoảng năm 1930. Các sản phẩm thương mại hỗn hợp phức tạp của congeners, tạo ra clo hóa của biphenyl. Hầu hết trong số đó là chất lỏng nhớt rất ổn định, độ dẫn điện thấp và áp suất hơi thấp. Các ứng dụng. | CHAPTER 6 Polychlorinated biphenyls and polybrominated biphenyls Background The PCBs and PBBs are industrial chemicals that do not occur naturally in the environment. The properties uses and toxicology of the PCBs are described in detail in Safe 1984 and EHC 140 PBBs are described in Safe 1984 and EHC 152. PCBs were first produced commercially around 1930. The commercial products are complex mixtures of congeners generated by the chlorination of biphenyl. Most of them are very stable viscous liquids of low electrical conductivity and low vapour pressure. Their principal commercial applications have been 1 as dielectrics in transformers and large capacitors 2 in heat transfer and hydraulic systems 3 in the formulation of lubricating and cutting oils and 4 as plasticisers in paints and as ink solvents in carbonless copy paper. With such a diversity of uses they entered the natural environment by many different routes before they were subject to bans and restrictions. The level of chlorination determines the composition and properties and ultimately the commercial use of PCB mixtures. Depending on reaction conditions levels of chlorination ranging from 21 to 68 percentage by weight have been achieved. The commercial products are known by names such as Aroclor Clophen and Kanechlor usually superseded by a code number which indicates the quality of 2001 C. H. Walker 122 Major organic pollutants the product. Thus in one series of products Aroclor 1242 and Aroclor 1260 contain approximately 42 chlorine and approximately 60 chlorine respectively. The first two numbers of the code indicate that the product is derived from biphenyl the second two indicate the approximate level of chlorination. Since the discovery of pollution problems during the 1960s the production of PCBs has greatly declined and there are few remaining uses at the time of writing. PBBs have also been marketed as mixtures of congeners produced in this case by the bromination of biphenyl. The main .

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