Similar term(s): polychlorinated biphenyls.
Polychlorinated biphenyls (PCBs) are a family of 209 congeners of structurally
similar organic chemicals, ranging from oily liquids to waxy solids. There are
12 PCBs that are dioxin-like and can
similarly be toxic and non-toxic. One
dioxin-like PCB is 3,4,4',5-Tetrachlorobiphenyl.
PCBs are synthetic and produced either as a singular congener, as a
homogeneous group or as a mixture. They are non-flammable, stable, have a high
boiling point and exhibit electrical insulating properties. As such, PCBs have
been used as coolants and lubricants in transformers and other electrical
equipment, as hydraulic fluids, and as plasticizers, pigments, dyes and
carbonless copy paper ink. They are also generated and released into the
environment as waste byproducts of chemical manufacturing and incineration.
Each PCB molecule contains two phenyl rings. A phenyl ring is a ring of 6
carbon atoms to which hydrogen atoms are attached. In PCBs, one or several
chlorine atoms replace some of these hydrogen atoms. The two rings in a PCB
molecule can rotate around the bond connecting them.
Depending on where the chlorine atoms are located, the two rings of a specific
PCB will either:
- lie approximately in the same plane (coplanar PCBs) or
- lie in different, more perpendicular planes (non-planar
Coplanar PCBs are considered to be most toxic, based on combined health
effects considerations. They are also referred to as “dioxin-like”.
Structure of dioxins:
Congener - Dioxin(s) - Dioxin-like - Non toxic - Toxic