Essay on Accumulation of Harmful Chemicals in Food Chains


The accumulation of harmful chemicals such as pesticides in the living organisms like plants, animals and humans (men) unknowingly, through the food chain, is called bioconcenfration of pesticides. This happens as follows.

Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests (harmful small animals) and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants along with water and other minerals.

When herbivorous animals eat plant food, then these poisonous chemical pesticides go into their bodies through the food chain. And when the carnivorous animals eat herbivores, then the pesticides get transferred to their bodies.


Man being an omnivore, eats plant food as well as herbivores. So, the pesticides present in plant food and herbivores also get transferred to the man’s body through food. Thus, pesticides enter the food chain at the producer level (plant level) and in the process of transfer of food through food chains these harmful chemicals get concentrated at each trophic level.

The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification.

Pesticides are non-biodegradable chemicals, so they get accumulated at each trophic level. Since humans occupy the top level in any food chain, so the maximum amount of harmful chemical pesticides gets accumulated in our bodies.

This damages our health gradually. Tests have shown that the most commonly used pesticide DDT is accumulating in our bodies through the food chains. Please note that the pesticides present in our food grains (like wheat, rice), fruits, vegetables, and meat cannot always be removed by washing, etc. Let us solve one problem now.


Sample Problem:

Which of the following will have the maximum concentration of harmful chemicals in its body?

Peacock, Frog, Grass, Snake, Grasshopper



In order to answer such questions, we should first write the food chain involving the given organisms. The organism which occurs at the highest trophic level (on the extreme right side) in the food chain will have the maximum concentration of harmful chemicals in its body. In this case, grass is eaten by grasshopper; grasshopper is eaten by frog; frog is eaten by snake and finally snake is eaten by peacock. So, the food chain will be:

Grass —— > Grasshopper —— > Frog —— > Snake—— > Peacock

In this food chain, since peacock occurs at the highest trophic level (on the extreme right side), therefore peacock will have the maximum concentration of harmful chemicals in its body.

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