Biphenyl đã polyclo hóa (PCBs) và biphenyl đã polybrom hóa (PBBs) là những 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), Robertson và Hansen (2001), và các tiêu chí sức khoẻ môi trường 140. PBBs được mô tả trong Tiêu chuẩn sức khỏe an toàn (1984) và môi trường 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. | 6 Polychlorinated Biphenyls and Polybrominated Biphenyls BACKGROUND The polychlorinated biphenyls PCBs and polybrominated biphenyls 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 Robertson and Hansen 2001 and Environmental Health Criteria 140. PBBs are described in Safe 1984 and Environmental Health Criteria 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 vapor 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 4. As plasticizers 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 The commercial products are known by names such as Aroclor Clophen and Kanechlor usually superseded by a code number that indicates the quality of the product. Thus in one series of products Aroclor 1242 and Aroclor 1260 contain about 42 chlorine and about 60 chlorine respectively. The first two numbers of the code indicate that the product is derived from biphenyl and the second two indicate the approximate level of chlorination. Since the discovery of pollution problems in the 1960s the production of PCBs has greatly declined and there are few remaining uses at the time of writing. Further details of the regulation of PCBs internationally are .
