PCBs readily penetrate skin, PVC (polyvinyl chloride), and latex (natural rubber)..In PCBs, some of the hydrogen atoms in biphenyl are replaced by chlorine atoms.Because of their lower toxicity, they are of less concern to regulatory bodies.The only North American producer, Monsanto Company, marketed PCBs under the trade name Aroclor from 1930 to 1977.Some PCBs share a structural similarity and toxic mode of action with dioxin.
As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease.
About 130 different individual PCBs are found in commercial PCB products. In terms of their structure and toxicity, PCBs fall into 2 distinct categories, referred to as coplanar or non-ortho-substituted arene substitution patterns and noncoplanar or ortho-substituted congeners.
The coplanar group members have a fairly rigid structure, with their two phenyl rings in the same plane.
The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with one to four chlorine atoms.
Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1 ng/m³ or more.