Environmental Engineering Reference
In-Depth Information
content of the animal. Therefore, fatty predatory fishes (e.g.,
bluefish) will have higher concentrations than less fatty fish
(e.g., striped bass) at the same trophic level in the same loca-
tion. Chemicals tend to increase with the age and size of the
animal. For animals high on the food web, food is the major
source of uptake. Fish can accumulate PCBs directly from sed-
iments and food. The amount of accumulation may be affected
by the prey, the magnitude of contamination, movement pat-
terns, trophic level, growth rate, and length of exposure (i.e.,
age). Female fish are able to eliminate some of their PCBs by
putting them into the eggs (yolk is very rich in lipids to which
PCBs bind). This accounts for observations such as those of
Haim von Westernhagen and colleagues of female fish having
lower PCB levels than males. While it is good for the female to
reduce her PCBs, it doesn't seem like a good long-term strategy
for the sensitive early life stages of the next generation to start
out life with a built-in dose of these chemicals. Marine birds
and mammals, high in food webs, accumulate high concentra-
tions of PCBs and chlorinated pesticides. Walruses and whales
in the far north, far from any use of such chemicals, also have
high concentrations. Similar to the situation of fish with eggs,
nursing mammals pass high levels on to their babies, which
then start off their lives with elevated body burdens of toxic
chemicals.
How do organisms metabolize organic contaminants?
PAHs (polycyclic aromatic hydrocarbons), which are accumu-
lated primarily in the liver, can be transformed into chemi-
cals that can be excreted via the gills and kidneys. There is
an enzyme system that breaks down these chemicals. The
enzymes responsible for oxidation of foreign compounds are
called mixed function oxidases (MFOs), which include the
highly studied cytochrome P-450 (CYP) system. Found in
many organisms and tissues, CYPs are involved in metabo-
lism of a wide range of organic compounds including PAHs,
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