DDT,BHC and aldrin all are chemical pesticides. DDT is the organochloride pesticide, which persists in environment as it not easily degraded also caused biological magnification or food chain concentration, ie, continuous increase in concentration of a toxicant at successive trophic levels in food chain. BHC and aldrin (cyclodienes) are also quite stable and have long residual action, they are, therefore, particularly valuable where protection is required for long period. Their toxic action is not fully understood, but they are known to disrupt nervous system.