Polychlorinated Biphenyls
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Polychlorinated Biphenyls
Polychlorinated biphenyls are a family of man-made chemicals that contain two
hundred and nine individual compounds with varying toxicity. Many different
combinations are possible. In chemical terminology, “phenyl” denotes a ring
structure of six carbon atoms attached to something else; “biphenyl” results
when two such rings are attached to each other. Polychlorinated biphenyl (PCB)
is any molecule having multiple chlorine atoms attached to the carbon atoms of a
biphenyl nucleus. Chlorine atoms can be placed at any or all of ten available
sites. PCB’s have been used widely as coolants and lubricants in transformers,
capacitors, and other electrical equipment. The manufacture of PCBs stopped in
the United States in October 1977 because of evidence that PCBs accumulate in
the environment and may cause health hazards for humans. Although PCBs are no
longer manufactured, human exposure still occurs. Many older transformers and
capacitors still contain fluids that contain PCBs. The useful lifetime of these
transformers can be thirty years or more. Prior to 1977, certain occupational
settings had, and may still have, higher levels of human exposure. Animal
experiments have shown that some PCB mixtures produce adverse health effects
that include liver damage, skin irritations, reproductive and developmental
effects, and cancer. With these observations, it is most considerably dangerous
for humans. The U.S Department of Health and Human Services has determined that
PCBs may reasonably be expected to be carcinogens. Human studies to date show
that irritations, such as acne-like lesions and rashes, can occur in PCB-exposed
workers. Other studies of people with occupational exposure suggest that PCBs
might cause liver cancer. Reproductive and developmental effects may also be
related to occupational exposure and eating of contaminated fish. While the role
in producing cancer, reproductive and developmental effects can not be clearly
determined, the suggestive evidence provides an additional basis for public
health concerns about humans who might be exposed to PCBs. It has also been
suggested that chemicals such as PCBs in the environment can mimic the body’s
natural hormones. This could lead to infertility, certain types of cancer, and
other hormone-related disorders. In the past, discharges of PCB-filled wastes
into rivers, streams and open landfills were considered acceptable, legal and
hazard-free practices. PCBs were also sometimes inte...
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