DDT was once a potent insecticide whose use is now banned in
the United States because of its toxic effects.
31. As one proceeds up to higher trophic levels, the amount
of DDT at a particular level increases. This process is known as biomagnification.
Essentially, if DDT runs off into a body of water, then the
plankton will ingest small amounts of the toxin. Because the toxin does not
leave the body, it accumulates in body tissues. Small fish eat the plankton,
and because they eat so many plankton in a life time, the concentration of DDT
increases in their tissues. As a large fish eats many small fish, the relative
amount of DDT increases in their tissues, sometimes enough to cause cancer or
other deformities in their bodies. Ospreys, which are at the top of this food
chain eat many of the toxic, DDT containing fish. They are getting large doses
of DDT in their diet. This causes a weakening of their bones (causing breaks)
and more importantly a drastic decrease in the amount of calcium in their egg
shells, so that the eggs crush easily.
Humans, being at the top of many food chains also accumulate
many toxins. Many of our cancers and birth defects may be the result of this
problem. For example, DDT-like chemicals seem to be increasing the infertility
of males (inability to make sperm). What would happen if no human males could
reproduce?
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Slichter