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Human Health
Pros & Cons

How do Pesticides affect ecosystems?



Pesticides can travel great distances through the environment.  When sprayed on crops or in gardens, pesticides can be blown by the wind to other areas.  They can also flow with rain water into nearby streams or can seep through the soil into ground water.  Some pesticides can remain in the environment for many years and pass from one organism to another. 

Pesticides differ according to their effects on various organisms.  Selective pesticides are toxic only to the target pests.  They cause little or no harm to other organisms.  However, nonselective pesticides can harm--or even kill--organisms that are not considered pests. 

How can pesticides be harmful to ecosystems?

Pesticide poisonings of people, livestock, and wildlife have occurred when proper care was not taken. Pesticide applicators must be very careful to avoid these risks. Mishandling of pesticides can lead to

  • Reduced control of the target
  • Injury of non-target plants and animals
  • Environmental damage.
  • May disrupt the natural balance in ecosystems

What types of pesticides are harmful?

In general, insecticides generally are the most toxic pesticides to the environment, followed by fungicides and herbicides.

The most hazardous pesticides include those that can be distinguished on the basis of:

1.    Water solubility

2.    Fat solubility

Water soluble pesticides are easily transported from the target area into ground water and streams since the pesticides get dissolved in the water. This means that the pesticides may run off to other areas and cause damage to un-targeted animals and plants in other places.

Fat soluble pesticides are readily absorbed in insects, fish, and other animals, often resulting in extended persistence in food chains.


Organocholirne pestcides such as DDT are fat soluble pesticides. the following picture shows how these pesticides enter through the bodies of animals by a process of biamplification.


1.    When there is a small amount of pesticide in the environment, it will enter the bodies of the animals that are low in the food chain - grasshoppers

2.    Even though there is only a small amount of the toxin in each grasshopper, the shrews will receive a larger amount of the toxin in its body because the shrew will eat many grasshoppers.

3.    When the secondary consumer is eaten (shrews), the higher-level predator, the owl will get all of its toxins, plus those of all the other prey it eats.

This means that the higher the trophic level, the greater the concentration of toxins. This process is referred to as Bioamplification.

Therefore the top carnivore which has the higher trophic level which is the owl, will be the most badly affected as it will obtain the most concentrated toxins.

This will lead to a decline of the population of owls because a lot of owls will be poisoned and dead. If there would be a decline of the owls, there would be a dramatic increase of the population of shrews as there would not be many predators, and if this happens there will be a decrease in the population of grasshoppers as they will be more predators (shrews) to eat them.

All of this comes to a final conclusion about pesticides:

1.    Pesticides damage ecosystems

2.    Pesticides may damage or harm un-targeted animals

3.    Pesticides decrease biodiversity

4.    Pesticides may cause a decline in populations or even cause extinction of species

5.    Pesticides “mess up” food chains/webs

6.    Pesticides disrupt the natural balance in ecosystems

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