Environmental Engineering Reference
In-Depth Information
1999). Unfortunately, it is carcinogenic and harms aquatic life (particularly
photosynthetic organisms) at levels of 2
g liter
1
(Carder and Hoagland,
1998). If the use of atrazine is discontinued, the compounds that are sub-
stituted may be worse (Vighi and Zanin, 1994). However, given its persis-
tence and water solubility, better management practices are necessary to
keep atrazine from entering the surface waters in many agricultural areas.
Some of the toxic organic compounds found in aquatic systems move
through the atmosphere. Research has demonstrated that persistent
organochlorine compounds are found worldwide (Simonich and Hites,
1995). The compounds condense from the atmosphere depending on tem-
perature, with the most volatile organics condensing in the polar regions
(Wania and Mackay, 1993). Atmospheric transport, in combination with
biomagnification of a long food chain, can account for the unusually high
concentrations of the toxic organic compound toxaphene in fish collected
from a remote subarctic lake (Kidd
et al.,
1995). One would assume this
lake is a pristine habitat because it is far from civilization. The fact that a
toxic organic compound contaminates fish in the lake illustrates the per-
vasive nature of human impacts on aquatic environments.
Petroleum products are another source of aquatic contamination. Urban
runoff is a significant source of oil contamination, with about 1 g per person
per day (Laws, 1993). Multiplying this by the U.S. urban population of 200
million yields 7.3
10
10
g (about 14 million gallons) of oil entering aquatic
habitats per year. Much of this oil is likely consumed by microbes or flows to
the ocean; the absolute damage to freshwater aquatic habitats is not known.
Another common source of contamination is
leakage from underground gasoline storage
tanks into groundwater. Cleaning spills from
such leaks has cost billions of dollars.
Oil and gas also leak into aquatic ecosys-
tems from outboard engines used on water-
craft. Visible slicks of oil and gas are com-
monly observed around busy marinas.
Engine exhaust also pollutes water. Two-
stroke engines release more pollution than
four-stroke engines. The organic compounds
in the exhaust of both engine types can kill
zooplankton and bacteria. A 15-kW (20-hp),
two-stroke engine that operates for 1 h
makes 11,000 m
3
of water undrinkable by
causing bad taste and odor. Expensive treat-
ment is required to reverse these effects (Jüt-
tner
et al.,
1995).
Chlorinated hydrocarbons such as poly-
chlorinated biphenyls (PCBs) are of concern
in aquatic systems because of their possible
carcinogenic properties. In addition, many
municipal sewage plants treat their final efflu-
ent with chlorine to kill pathogens and this
treatment forms chlorinated hydrocarbons.
Many municipalities are switching to ultravi-
olet radiation treatment schemes instead.
cases of influence of environmental estrogens
include male fish in polluted waters that pro-
duce abnormal amounts of the egg yolk pro-
tein normally produced by female fish and sex
reversals of turtles when exposed to estro-
genic chemicals. Ecoestrogens can bioaccu-
mulate and be passed to offspring (Crews
et
al.,
2000). This can cause harm to invertebrates.
Some researchers attribute the highly con-
troversial reports of reduced human sperm
counts to environmental chemicals. Endocrine-
disrupting compounds have also been linked
to formation of human cancers (Gillesby and
Zacharewski, 1998). Apparently, combinations
of organic chemicals can also activate the es-
trogen receptor (Arnold
et al.,
1996). Such in-
advertent biological signaling may have far-
reaching and unpredictable effects in aquatic
habitats. Fortunately, standard water purifica-
tion techniques can remove ecoestrogens
(Fawell
et al.,
2001). Regardless of the strength
of an individual claim, the topic of ecoestro-
gens illustrates that wholesale release of or-
ganic contaminants into the environment can
have unintended effects.
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