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Science 9 – Unit C:
Environmental Chemistry
Topic 2: A Growing Concern
Pesticides and DDT
Pesticide use is increasing worldwide as agriculture
continues to develop. There are three common
varieties of pesticides: insecticides (kill bugs),
herbicides (kill weeds), and fungicides (kill harmful
fungi and diseased crops).
DDT – 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
Resistance – 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.