What do you understand by biomagnification? Explain it.

(N/A) Biomagnification refers to the increase in the concentration of toxic substances (such as non-biodegradable pollutants like $DDT$ or mercury) at successive trophic levels in a food chain.
This phenomenon occurs because the toxic substance accumulated by an organism cannot be metabolized or excreted,and is thus passed on to the next higher trophic level in a higher concentration.
For example,in an aquatic food chain,the concentration of $DDT$ increases from water to phytoplankton,then to zooplankton,small fish,large fish,and finally to fish-eating birds,where it reaches a toxic level that can interfere with calcium metabolism,leading to the thinning of eggshells.