FREE ESSAY ON PCBS

PCBS

PCBs: 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
intentionally released into the environment to reduce dust emissions from dirt roads, or
as extenders in some agricultural pesticides formulations. These practices were
inappropriate and potentially harmful. There have also been accidental releases of PCB
and associated contaminants into the environment via leaking of sealed PCB fluid
compartments during commercial use of transformers and capacitors, as a result of
improper disposal of PCB-containing equipment or chemical products. The contamination of
food for animal and human consumption has also occurred from PCBs leaking from
malfunctioning heating coils into foods during manufacturing. PCBs can also enter the
food chain through the ingestion of contaminated fish from PCB-contaminated water.
Finally, transformer and capacitor fires have led to the environmental release of PCBs
and thermal degradation products.
Concern about the presence of PCBs in our environment began around 1966 when research in
Sweden revealed the presence of PCBs in environmental samples being screened for DDT.
Further study confirmed suspicions that the rate of natural breakdown was very slow for
some of the PCB congeners. Concern continued to rise due to
widespread human poisoning episodes in 1968 and 1978. PCBs are now regarded as
environmental contaminants that build up in the food chain. They build up in the food
chain due to their relative insolubility in water and high solubility in fats. 
To date, there are tests to determine PCBs in blood, body fat and breast milk. These
tests are not routine clinical tests, but they can detect PCBs in members of the general
population as well as in workers with occupational exposure to PCBs. Although these tests
indicate if one has been exposed to PCBs, they do not predict potential health effects.
Blood tests are the easiest, safest and perhaps, the best method for detecting recent
large exposures. As well as tests, remediation techniques and disposal technologies
continue to evolve. Many approaches have been tested out but none has emerged as a
technically and economically viable solution for the endless environmental situations
encountered. A useful method for cleansing water will probably not be effective in
treating soil. Highly chlorinated PCBs will not be as readily decomposed as
less-chlorinated PCBs. These types of factors contribute to the challenge of effective
and cost-efficient remediation of PCB contaminated sites. Bacterial build-up or breakdown
of PCBs in soil and sediment is potentially useful technology that is receiving much
attention. Introductory results on the breakdown of soil samples, including those taken
from the Hudson River, show promise. A "thermal blanket" approach, in which soil is
heated from the surface downward and PCBs are removed under vacuum, is also investigated.
Another approach to reduce PCB problems is finding alternatives to PCBs.
There are various chemical alternatives to PCBs (including silicon fluids, fluorocarbons,
high molecular weight hydrocarbons, low molecular weight chlorinated hydrocarbons and
high boiling oils and esters) which will work in electrical equipment; however, a
transformer constructed for use with PCB fluid may not operate at the same power load
with a substitute chemical. Such a transformer becomes less efficient, resulting in a
higher operating cost as well as added risk of fire. Precautionary measures must be taken
to ensure fire safety and proper disposal of waste. Clearly shifting from PCBs to
alternatives has involved tradeoffs, but not elimination, of health and safety risks.
In conclusion, because of the ban on PCB production, decreasing use of PCBs and efforts
to remediate contaminated sites, general population exposure to PCBs in fish and other
foods has been significantly reduced, and PCB levels in human blood are also decreasing.
Industry and government should focus on the development of novel and cost-effective
remediation and disposal techniques, as well as on scientifically improved health risk
analysis to reduce the uncertainty associated with PCB exposure and health effects in
humans.
Bibliography
Work Cited Page
Internet, Polychlorinated Biphenyls, 'Yahoo' 1992
http://mail.odsnet.com/TRIFacts/92,html
Internet, Organochlorine and Metal Pollution, 'About' 04/20/98
http://chemistry.about.com
Wall, E. Byron, Science in Society, Wall & Emerson, Inc. Toronto, Ontario. 1989
Pages 326-329