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Developed
in the early 1900's, Polychlorinated biphenyls (PCBs) are
chlorinated oils that remain stable when subjected to heat
and pressure. These traits, combined with their high electrical
resistance, made them ideal for use in insulators, transformers
and capacitors. PCBs performed well in those initial applications
and their use expanded into hydraulic fluids, casting wax,
carbonless carbon paper, compressors, pigments, adhesives
and fluorescent light ballasts.
Polychlorinated biphenyls make up a group of 209 individual
chlorinated biphenyl rings know as congeners. A PCB is typically a
mixture of 60 to 90 congeners. As the number of chlorines in a PCB
mixture increases the flash point rises and it becomes less
biodegradable.
Once dispersed
into the environment, PCBs tend to concentrate, or bioaccumulate, in
animals at the top of the food chain.
Organochlorine
pesticides are insecticides composed primarily of carbon, hydrogen
and chlorine. They break down slowly and can remain in the
environment long after they are applied and in organisms long after
exposure.
The most
notorious organochlorine is the insecticide DDT (Dichloro diphenyl
trichloroethane). Promoted as a "cure all" insecticide in the 1940s,
DDT was used globally for many years in agricultural production and mosquito control.
For
a copy of EPA Method 608, click here
Click
to download a copy of a Horizon Technology Application
Note on EPA Method 608
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