C-2 Notes


Science 9 – Unit C:

Environmental Chemistry

Topic 2: A Growing Concern

Pesticides and DDT


use is increasing worldwide as agriculture continues to develop. There are three common varieties of pesticides:


(kill bugs),


(kill weeds), and


(kill harmful fungi and diseased crops).


– An insecticide that was widely used in the past. It was originally thought that the DDT only would affect the insect populations, however, because the insects were part of food webs, the poisonous effects of DDT spread and multiplied to other species including eagles where the effects of

DDT decimated their populations.


The increase of the concentration of a chemical as it moves up the food chain.

Because DDT is so effective at killing problem insects which spread disease (ie. Mosquitoes) it is still widely used in the Third World where diseases such as malaria and typhus have killed thousands.

The choice here is between letting endangered species of animals and crops die and letting young and old persons die.

There is a constant struggle to create newer pesticides that break down quickly in the environment after they do their job. However there is another problem that is caused by using chemical pesticides:



– As chemical pesticides do their job, the tiny minority of the species that is resistant to the chemical breed and multiply and the new population of the species are now entirely resistant requiring that the chemical be made stronger and the cycle of escalation starts.

A possible solution to the problem of resistance is to use non-chemical pesticides such as using animals such as ladybugs which eat aphids and other harmful bugs.