Environmental Engineering Reference
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marine mammals. Polar bears, living far away from any
source of contaminants but at the highest trophic level in the
Arctic where contaminants concentrate, seem to be exhibiting
abnormal genitalia.
What are biomarkers?
Biomarkers are changes (generally biochemical) that can be
used to assess responses to contaminants. Some molecular
biomarkers include the induction of cytochrome P-450 1A (or
CYP1A), which indicates exposure to aromatic hydrocarbons
and is an enzyme system that is used to metabolize them.
Another biomarker is vitellogenin (yolk protein) production in
males, which indicates exposure to estrogenic chemicals and
is normally produced only by females. The eggshell thinning
of birds described above could also be considered a biomarker.
What kinds of population level effects can be produced?
Population level effects such as reduced numbers can be seen
from chemicals that do not necessarily have direct impacts on
reproduction. For example, chemicals that are neurotoxic can
affect behavior, including reproductive behavior. If reproduc-
tive behavior is abnormal, reproduction will be impaired and
the population may diminish. If the chemicals affect feeding
behavior and the organisms eat less, they will not grow as
well and may not be able to reproduce as well or live as long
as unaffected individuals. If contaminants impair the ability
to avoid predators, the animals will not live as long and may
not leave offspring. If chemicals affect the immune system, the
organisms will be more vulnerable to diseases. These are just
some of the ways that populations could decrease as a result
of contaminant exposure. Populations in chronically polluted
areas can also respond by becoming more tolerant to the con-
taminants, which can select for more tolerant individuals. This
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