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HUMAN INFLUENCES ON THE ENVIRONMENT
DDT was an insecticide used widely in the 1940's and 1950's. DDT is a very resistant chemical. This means that it does not break down into less harmful chemicals very easily.
All living things are linked in at least one food web. DDT passed through the food webs because it was washed into the soil by rain. It also reached lakes and sea water.
The following food chain exists in California where DDT had been sprayed to kill gnats.
Drawing of a Grebe
Although the amount of DDT was found to be very dilute in the water, the grebes, which are fish-eating birds, died in large numbers after a period of time.
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