Environmental Engineering Reference
In-Depth Information
centrated in fats and have little solubility in water. As a result, when an anim-
al takes in an organochlorine molecule, it is unlikely to excrete it. Therefore,
the animal accumulates more and more of the substance until it eventually
dies (most probably by being eaten). Biomagnification simply reflects that a
food web consists of a lower level of primary producers that accumulate the
organochlorines from the nonliving environment and whose organochlorine
“harvest” is progressively squeezed into fewer and fewer individuals as they
pass up the food web. The top predator accumulates the grand total of all the
organochlorine intake of all the plants and animals in the trophic levels below
that have contributed to its meals. A coastal or lake food web could see plant
plankton (phytoplankton) passing their cumulative burden initially to herbi-
vorous zooplankton, then through carnivorous zooplankton to small fish to
large fish to the gull, osprey, otter or seal. The cost the gull pays for being
well fed is to potentially end up with a body burden about 25 million times
higher than the concentration in coast or lake waters in which our gull takes
its daily paddle. Of course, it is not a problem if there are no contaminants
that are capable of being biomagnified in the water.
Figure 8.1
provides a
simplified view of the Arctic marine food web with its opportunities for dif-
ferent degrees of biomagnification.
3.
Organochlorines are toxic, but this toxicity takes several forms. Each substance
is associated with a number of acute effects that are fairly simple to detect.
However, hidden below this is an array of other outcomes associated with
long-term (chronic) exposure even at much lower doses. We will look at these
later, but they come in a large variety of forms, ranging from increased incid-
ences of tumours to reproductive tract and fertility abnormalities to behavi-
oural effects. It is an old tenet of toxicology dating from Paracelsus (a Swiss
physician and polymath who lived between 1493 and 1541) that the dose
makes the poison. If you combine this thought with the organochlorine bio-
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