polychlorinated biphenyl (PCB)

Definition

Derivative of biphenyl (C6H5C6H5) synthesized by replacing some of the hydrogen atoms in the benzene ring by chlorine atoms. Used mainly as flame retardants, insulators, and plasticizers, PCBs are linked to liver and kidney damage, birth defects, miscarriages, sterility, and cancerous tumors. Banned since 1979, they persist in nature because (being water insoluble) they cannot be washed away but (being fat soluble) accumulate in body tissue (see bioaccumulation) and move up the food chain.