Geoscience Reference
In-Depth Information
polyhalogenated aromatic hydrocarbons from transmission pipes and pipe connec-
tions are considered as secondary sources. Wastewaters of point sources include
many compounds such as phenols that also are found in nonpoint sources. Domestic
and industrial chemicals diffuse into aquatic systems via contaminated soil, urban
surface run-off, surface run-off from agricultural areas, and from construction sites.
Organic chemicals having adverse effects on the aquatic environment mostly belong
to this latter group. Nonpoint sources include pesticides, such as chlordane and
carbofuran; solvents, such as trichlorobenzene and tetrachloroethylene; metal redac-
tors, such as trichloroethylene and trichloroethene; monomers and plasticizers, such
as polychlorinated biphenyls; and polycyclic aromatic hydrocarbons from coal
combustion units.
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4.2.2
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LASSIFICATION
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RGANIC
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HEMICALS
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HAT
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IGHT
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PPEAR
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NVIRONMENTS
Combustion products of liquid petroleum products and coal
. The global annual
production of liquid petroleum products (e.g., gasoline, kerosene, heating oils)
is about 3 billion metric tons. Producing, transporting, processing, handling,
storing, using, and disposing of these hydrocarbons pose numerous problems.
Properties of various forms and compounds that interact with the environment
include some easily vaporize; some bind to solids; some oil hydrocarbons are
extremely nonreactive; some interact with light; some are quite nontoxic; and
some are carcinogenic. The various properties of these chemicals are factors in
the environmental threat.
Halogenated methanes, ethanes, and ethenes
Some of these compounds are
inert and nonflammable, depending on the type and number of halogen substituents.
Some exhibit physical properties that make them useful as aerobic propellants,
refrigerants, blowing agents for plastic foams, and solvents for such purposes as dry
cleaning and metal degreasing. Some of these chemicals are flammable and toxic,
and a few are used as pesticides.
Over 85% of fluorocarbons (freons) manufactured are released into the atmo-
sphere. These compounds are thought to be responsible for depleting the strato-
spheric ozone layer. The chlorinated solvents, dichloromethane and tri- and
tetrachloroethane, are among the top ten organic groundwater contaminants.
These compounds are quite persistent and mobile in groundwater, and their
contamination of groundwater can, in turn, lead to contamination of coastal
waters.
Polyhalogenated aromatic hydrocarbons
.
Because of their tendency to bioaccu-
mulate, these chemicals, for example polychlorinated biphenyls (PCBs), have
attracted considerable attention. More than 1 million metric tons of PCBs have been
produced and used as capacitor dielectrics, transformer coolants, hydraulic fluids,
heat transfer fluids, and plasticizers. PCBs are commonly applied as complex mix-
tures of congeners (i.e., isomers and compounds exhibiting different numbers of
chlorine atoms but originating from the same source) and enter the environment
mostly from production, storage, and disposal sites. PCB use has been restricted in
numerous countries; however, PCBs are still ubiquitous in the environment.
.
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