Environmental Engineering Reference
In-Depth Information
What are the trends in pesticide contamination?
Persistent contaminants in coastal sediments and biota in
the United States have been generally decreasing over the
past two decades. The National Oceanic and Atmospheric
Administration (NOAA) has run a monitoring program for
140 contaminants in bivalve populations (mussels and oys-
ters) in 300 sites nationwide. For butyltins (TBT having been
banned), 88 sites showed a significant decrease while none
showed an increase. For organic contaminants such as chlo-
rinated hydrocarbon pesticides (most of which were banned
in the United States in the 1970s and 1980s), 133 sites showed
a significant decrease while none showed an increase. The
Canadian government has been monitoring contaminants in
bird eggs and has found decreases in chlordane, dieldrin, and
DDT-breakdown product DDE (banned pesticides) in eggs of
the great blue heron, double-crested cormorant, and osprey.
What are polychlorinated biphenyls (PCBs)?
Polychlorinated biphenyls (PCBs) are also chlorinated hydro-
carbons, and were manufactured from 1929 until they were
banned in the United States in 1979 (Figure 6.2). PCBs are chem-
ically related to organochlorine pesticides. Each molecule con-
sists of chlorine atoms attached to a double carbon-hydrogen
ring (a biphenyl). There are 209 different PCB molecules (or
congeners) that differ in the number and location of the chlo-
rine atoms on the rings. In general, PCBs with more chlorine
atoms are more toxic than PCBs with less chlorine. Like chlori-
nated hydrocarbon pesticides, they remain in the environment
for a long time, have low water solubility, and accumulate
in fat. PCBs are suspected of causing cancer and have been
linked to male sterility and birth defects. In birds and fish they
decrease egg hatchability, alter behavior, and decrease immune
response. There are two distinct categories of PCBs: coplanar
and non-coplanar (or
ortho
-substituted) congeners. Coplanar
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