| environ. |
polychlorinated biphenyl 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 enterthe food chain. PCBs are fat-soluble, and are therefore easy to take into the system, but difficult to excrete (PCBs是一种自然界不存的，只能通过人工合成的化合物。商用PCB混合物是清澈、淡黄色的液体，由氢原子替换联苯分子中的氯生成。由于其物理特性，PCBs常被用于电介质流体，例如电源变压器和电容器，并且在水力机械、真空泵、压缩机和热交换流体的电机设备中也被广泛应用。其它用途包括：润滑剂、荧光灯石碴、油漆、胶合、蜡、无碳型复印纸、墨水(包括报纸用墨水)、土路的灰尘控制、释放杀虫剂、乳化油溶剂等。PCBs是一种稳定的化合物。) |
