Biological magnification is defined as the increase in concentration of toxicants at successive trophic level in a food chain for example DDT.This is because these toxicants can not be metabolised or excreted. Hence, therefore it gets accumulated in an organism and pass on to higher trophic levels in a food chain. Biomagnification of DDT in aquatic food chain : DDT accumulates in the fish eating birds and disturbs calcium metabolism, which results in thinning of egg shells. This results in decline in the population of the fish eating birds. Flow chart of biological magnification.