Polychlorinated biphenyls (PCBs) are mixtures of synthetically chlorinated chemical compounds.  They usually take the form of oily liquids or waxy solids and have been used as coolants and lubricants in electrical equipment because of they are effective insulators and tend not to burn easily.  The U.S. stopped all manufacturing of PCBs in 1997 because of increasing concerns about their toxicity.  More than 1.5 billion pounds of PCBs were manufactured in the US alone, prior to its banning in 1977.[1]

Practical Uses

Environmental Effects

 PCB production has been banned, however the chlorinated chemicals do not break down very easily and are still encountered in the environment.  There are no natural sources of PCBs, so the chemicals found in the environment are reminants of previously used chemicals.  The most abundant source of PCBs is toxic waste leakage.  Much of the disposal of the manufactured PCBs has not been properly executed, resulting in environmental buildup.  PCBs can be transferred through various mediums including water and air.  They stick pretty readily to organic particles and thus can be transferred long distances from release sites.[3]

Health Effects

The most widely noticed health effect of PCB exposure is aggravated skin, including acne and rashes.  Experiments in animals show that large amounts of consumed PCBs can result in anemia, as well as liver, stomach, and thyroid gland damage.  It is also suspected that extensive PCB exposure is correlated with changes in the immune system, behavior, and reproduction complications.[4]

[4] http://www.atsdr.cdc.gov/toxprofiles/tp17-c3.pdf

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