$A$ farmer is using pesticides in his field. He uses the produce from his field as food for fish. He is told that the fish are not fit for human consumption because large amounts of pesticides were found in the fish cells. How is this possible? Explain.

(N/A) Pesticides applied to the crops are absorbed by the plants. When these crops are used as fish feed,the pesticides enter the fish's digestive system.
This process is known as $Biomagnification$. As the pesticides move from lower trophic levels to higher trophic levels through the food chain,their concentration increases.
Eventually,the concentration of pesticides in the fish becomes high enough to cause serious metabolic and physiological disturbances,making them unfit for human consumption.