Where do polychlorinated biphenyls come from?
Polychlorinated biphenyls (PCBs) are a group of 209 synthetic compounds. The compounds contain different numbers of chlorines and these can be attached in different ways. PCBs are stable at high temperatures, very volatile, attracted to lipids (fats), and they repel water. PCBs were first made in 1881, and industries began using them in 1929. PCBs were used in electric insulators, lubricants, hydraulic fluids, flame retardants, ink solvents, and waterproofing materials, among other products. After 1971, PCBs were most commonly used for insulating and cooling closed electrical systems such as capacitors and transformers. PCB manufacture and processing were stopped in North America in 1979 because of concerns for the environment and human health. Prior to restrictions, however, about 370,000 tonnes of PCBs are estimated to have been released to the environment across the globe. In the past, PCBs were released to soil by leaks from electrical transformers, wastes that had been spread over
