Spraying of DDT as an insecticide on vegetable crops should be banned because it leads to biological magnification or Biomagnification in the aquatic food chain. Biomagnification is the increase in concentration of the toxic substances at successive trophic levels as when a toxic substance is accumulated by an organism and cannot be metabolised or excreted then it is passed on to the next higher trophic level. The concentration of DDT increases at each trophic level.

A diagrammatic representation is given below: