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 enter the food chain. PCBs are fat-soluble, and are therefore easy to take into the system, but difficult to excrete. (Source: PZ / PHC)