Question

What is the main problem caused by the use of pesticides?
A. Their residues persist in water and other components of the environment.
B. Mosquitoes have become resistant to DDT.
C. They kill silkworms.
D. They deform the gills of some fishes.

Answer 1

Hint: Pesticides are chemical agents or a mixture of a chemical and biological agent which don’t degrade easily in the environment. Pesticides are used to protect crops from pests and weeds. They are not only harmful to the environment but also to humans.

Complete answer:
The main problem caused by the use of pesticides is that their residues persist in water and other components of the environment as they are not easily degraded in the environment. Pesticides are sprayed over the crop field to protect the crop. These poisonous chemicals come in contact with soil while staying and are washed off into deep layers of soil.
With the help of percolating rainwater they reach the underground water table and are passed to different water bodies through surface runoff. These chemicals can also enter directly into the plants.
These are non-biodegradable toxic chemicals which are passed from one trophic level to another trophic level, as they are not used by organisms during metabolic processes.
These harmful chemicals not only enter the food chain but also get concentrated at each successive trophic level by the process known as biological magnification.

Note:
Biomagnification or biological magnification is the increase in concentration of non biodegradable chemicals per unit weight of an organism with each successive rise in trophic level.
Trophic level- The specific place occupied by the organism in a food chain based on the source of their nutrition is called trophic level. A species may occupy more than one trophic level in the same ecosystem at same time.