Explain biomagnification and its effect in $DDT$.

(N/A) Biomagnification refers to the increase in concentration of toxic substances at successive trophic levels in a food chain.
This occurs because a toxic substance accumulated by an organism cannot be metabolized or excreted,and is thus passed on to the next higher trophic level.
In an aquatic food chain,$DDT$ (Dichloro-Diphenyl-Trichloroethane) is a classic example of biomagnification. The concentration of $DDT$ increases from water $(0.003 \ ppm)$ to zooplankton $(0.04 \ ppm)$,small fish $(0.5 \ ppm)$,large fish $(2 \ ppm)$,and finally to fish-eating birds $(25 \ ppm)$.
High concentrations of $DDT$ disturb calcium metabolism in birds,which causes thinning of eggshells and their premature breaking,eventually leading to a decline in bird populations.