Write a note on effect of various pesticides on living things.

Prior to World War $II$, many naturally occurring chemicals such as nicotine were used as pest controlling substance for major crops in agricultural practices.

During World War $II$, $DDT$ was found to be of great use in the control of malaria and other insect-borne diseases.

Thus, after the war, $DDT$ was put to use in agriculture to control the damages caused by insects, rodents, weeds and various crop diseases.

Therefore, as insect resistance of $DDT$ increased, other organic toxins such as Aldrin and Dieldrin were introduced in the market by pesticide industry.

Most of the organic toxins are water insoluble and nonbiodegradable. These high persistent toxins are, therefore, transferred from lower trophic level to higher trophic level through food chain.

Over the time, the concentration of toxins in higher animals reach a level which causes serious metabolic and physiological disorders.

Organo-phosphates and carbamates chemical are serious nerve toxins. As a result, such insecticides are responsible for the death of laborers working on the farm.