Environmental Engineering Reference
In-Depth Information
biomagnify and become most concentrated in carnivorous,
fatty, large fishes. They tend to build up primarily in fatty
tissue and to a less extent in muscle tissue. Scientists have
found over a dozen different chlorinated organic compounds
at higher concentrations in farmed salmon than wild salmon.
PCBs are not highly toxic with a single dose (as in a single
meal), but continued low levels of exposure (for example, eat-
ing contaminated fish over an extended period of time) may
be harmful. There are standards set by EPA and FDA for safe
levels of consumption. These numeric levels are based on
lab tests of high concentrations on rats or mice followed by
extrapolation downward to estimate what level would be safe
in the rats or mice, and then extrapolation from rodents to
people— so there is a large amount of uncertainly about these
numbers, and no one should consider a concentration slightly
above the standard to be alarming or a concentration just
below it to be totally safe. The EPA considers PCBs to be prob-
able human carcinogens, because they cause cancer in labora-
tory animals. Other tests on laboratory animals show damage
from PCBs to the circulatory, nervous, immune, endocrine,
and digestive systems. Risks to humans are highest in the
fetus or nursing infant (as with Hg), when the mother is or
has been exposed to PCBs. Women of childbearing age, espe-
cially those pregnant or nursing, are advised to minimize risk
by avoiding eating fish from areas known to contain PCBs. In
terms of chronic low-level exposure to PCBs over time, less is
known about potential adverse health effects. However, sci-
entists suspect that long-term exposure to small amounts can
contribute to a variety of health problems including devel-
opmental problems in children, liver damage, and cancer.
Some studies showed that children of mothers who ate fish
from the Great Lakes with high PCBs had smaller head size,
reduced visual recognition, and delayed muscle develop-
ment. A mother's exposure to PCBs and other chemicals was
linked to slight effects on her child's birth weight, short-term
memory, and learning. Adults who ate fish containing PCBs
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