Polychlorinated biphenyls are a group of organic chlorinated chemicals that are entirely man-made. Their manufacture in the US was stopped in 1979 due to health concerns.
PCBs are chlorinated hydrocarbons (made up of carbon, hydrogen and chlorine atoms) with no taste or smell. They can be colorless or light yellow, oily or solid.
PCBs are good insulators, hence their various industrial uses:
However, in 1979 PCB use was forbidden in US-manufactured items. Most countries around the world have also banned its use, and nowadays PCBs can only be found in products made before 1979.
PCBs have been shown to cause serious health conditions. Most of them were identified in animals and are highly likely in humans, among which: