Biomagnification

Biomagnification is the bioaccumulation of a substance up the food chain by transfer of residues of the substance in smaller organisms that are food for larger organisms in the chain. It generally refers to the sequence of processes that results in higher concentrations in organisms at higher levels in the food chain (at higher trophic levels). These processes result in an organism having higher concentrations of a substance than is present in the organism’s food. http://toxics.usgs.gov/definitions/biomagnification.html
Organism which feed higher levels of DDT from consuming their prey , it is not poisonous in small amounts and eventually the DDT concentration accumulates to the extend that the top consumers suffer the effects of bioaccumulation