Environmental Engineering Reference
In-Depth Information
so resistant that a different chemical has to be used. Because of
their persistence in the environment and low water solubility,
chlorinated hydrocarbons tend to accumulate in sediments and
in tissues. Related pesticides included aldrin, dieldrin, chlor-
dane, heptachlor, and toxaphene, which caused fish kills when
applied near the water. Chlorinated hydrocarbons remain in
the environment (especially sediments) for many decades, so
they continue to be found long after they have been banned
and continue to be sources of contamination to marine life.
They can be moved by winds and currents far from their site of
origin; for example, pollutants from Europe, Russia, and North
America are transported to the Arctic. Furthermore, commer-
cial bottom trawling (pulling fishing nets across the bottom
to catch fish) churns up the sediments, releasing pollutants,
as shown by Lycousis and Collins. Furthermore, animals can
take up high levels of contaminants released by trawling. After
only one month of exposure, mussels living near the bottom
near trawling areas exceeded the EU limit for the chlorinated
chemicals that cause developmental and reproductive abnor-
malities, so the high levels in edible mussels are of particular
concern for public health.
Organisms can take up contaminants from the water, the
sediments, and from their food, and may acquire tissue lev-
els much greater than those in the environment. Not only do
these chemicals remain in sediments for a very long time,
they also biomagnify through food chains, increasing from
one step to the next. DDT and other chlorinated hydrocar-
bons concentrate in fatty tissues. Animals accumulate and
concentrate these chemicals from their food, and each tro-
phic level will have greater concentrations than the level
below it, so that the highest concentrations are in the top
carnivores—big fish, predatory birds, marine mammals,
and humans. Because of biomagnification, large carnivorous
fish may have hazardous levels of contaminants, and health
advisories may be issued to protect humans from consum-
ing them.
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