A polychlorinated biphenyls (PCBs) is a class of chemicals that were manufactured for industrial purposes as coolants and lubricants for electrical equipment until they were phased out in 1977. These highly persistent chemicals can still be found in older electrical equipment and in industrial waste sites.

PCBs can cause bronchitis, irritation of the gastrointestinal tract, nervous system impairment, fertility problems, and changes in liver function.

see also:
"polychlorinated biphenyls" is in the HS Code "2710.91"
- -- Containing polychlorinated biphenyls (PCBs), polychlorinated terphenyls (PCTs) or polybrominated biphenyls (PBBs)

Other /More definition:
A polychlorinated biphenyls (PCBs) is a group of synthetic, toxic industrial chemical compounds once used in making paint and electrical transformers, which are chemically inert and not biodegradable. PCBs were frequently found in industrial wastes, and subsequently found their way into surface and ground waters. As a result of their persistence, they tend to accumulate in the environment. In terms of streams and rivers, PCBs are drawn to sediment, to which they attach and can remain virtually indefinitely. Although virtually banned in 1979 with the passage of the Toxic Substances Control Act, they continue to appear in the flesh of fish and other animals.

see also:
"polychlorinated biphenyls" is in the HS Code "2710.91"
- -- Containing polychlorinated biphenyls (PCBs), polychlorinated terphenyls (PCTs) or polybrominated biphenyls (PBBs)