Environmental Engineering Reference
In-Depth Information
each compound. The chemicals are viewed by Harmison
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as falling into four
groups: (1) halogenated hydrocarbons and other organics, (2) heavy metals, (3)
nonmetallic inorganics, and (4) biological contaminants, animal and human drugs,
and food additives.
In group 1 may be polychlorinated biphenyls (PCBs); chlorinated organic
pesticides such as DDT, Kepone, Mirex, and endrin; polybrominated biphenyls
(PBBs); fluorocarbons; chloroform; and vinyl chloride. These chemicals are per-
sistent, often bioaccumulate in food organisms, and may in small quantities cause
cancer, nervous disorders, kidney and brain damage, and toxic reactions. A
recently recognized undesirable role for pharmaceuticals, herbicides, and pes-
ticides in natural waterways is as endocrine disruptors.
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The extraordinary
production and use of these compounds, coupled with their persistence through
wastewater treatment processes, has resulted in long residence times of such mate-
rials in the environment. Aquatic life have been impacted through the ability of
endocrine disruptor-active compounds to mimic hormonal control of reproductive
systems, organ development, and sensory functions. There is concern that con-
taminants falling into the category of endocrine disruptors may exist in finished
drinking waters. The route by which herbicides and pesticides may gain entry
to natural waters is through agricultural runoff. PCBs are no longer manufac-
tured, but their residues are still present in aquatic sediments and the tissues of
aquatic vertebrates and invertebrates. Other chlorinated compounds may appear
in soils and waters from leaking storage drums, uncontained industrial lagoons,
and accidental landfill leachates.
Another group of nine chlorinated compounds that may appear in drinking
water as a consequence of the use of chlorine as a post water treatment disinfec-
tant is the haloacetic acids or disinfection byproducts (DBP). Trihalomethanes
are a subset of the haloacetic acids that are regarded as the major carcinogens
among DBP in relation to colon and rectal cancers
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and reproductive disorders
including spontaneous abortions, fetal deaths, miscarriages, and birth defects.
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Precursors to the formation of DBP are naturally occurring organic molecules
present in raw water supplies. Unlike the plethora of organic substances referred
to in the AP report, DBP are regulated in the drinking water standards. However,
only five of the nine DPB compounds are monitored.
Group 2 includes heavy metals such as lead, mercury, cadmium, barium,
nickel, vanadium, selenium, beryllium. These metals do not degrade; they are very
toxic and may build up in exposed vegetation, animals, fish, and shellfish. Some
of them (e.g., lead, mercury, cadmium, and beryllium) have no role in human
metabolism and are inhibitors of enzymes at very low concentrations. As poisons,
they can affect the functions of various organs (e.g., kidney, liver, brain) and
damage the central nervous system, cardiovascular system, and gastrointestinal
tract. Children and pregnant women are especially vulnerable. The levels of heavy
metals in drinking water are highly regulated. Heavy metals variably appear in
many manufactured products, including metal goods and electronic devices, as
well as naturally occurring minerals and coal deposits. Hence, there is ample
opportunity for contamination of natural waters through runoff from insecure
