Environmental Engineering Reference
In-Depth Information
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FigureĀ 6.2 PCB (polychlorinated biphenyl) molecule, showing the various sites where
Cl atoms may be attached to carbon
PCBs have a fairly rigid flat structure, with the two phenyl
rings in the same plane, which gives the molecule a structure
similar to polychlorinated dibenzo-p-dioxins (PCDDs; see
below) and allows them to act in the same way as these mol-
ecules. Non-coplanar PCBs, with chlorine atoms at the ortho
positions, are not part of the extremely toxic dioxin group.
Nevertheless they have neurotoxic and immunotoxic effects,
but not at such low levels as those related to dioxins. Due to
their nonflammability, chemical stability, high boiling point,
and electrical insulating properties, PCBs had hundreds of
industrial and commercial applications including electrical
equipment; as plasticizers in paints and rubber products; in
pigments, dyes, and copy paper; and many others.
How did PCBs get into the marine environment?
Unlike pesticides, PCBs were never intentionally sprayed in
the environment. They were used in industry and got into the
environment through carelessness during their manufacture
and use. They can still be released into the environment from
poorly maintained hazardous waste sites, illegal or improper
dumping of PCB wastes, leaks from electrical transformers
containing PCBs, and disposal of PCB-containing products
into landfills not designed for hazardous waste. PCBs may
also be released to the environment by the burning of some
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