Our farmers still use DDT. Mercury and DDT are well known for biological magnification. Calcium metabolism in birds is disturbed which results in thinning of egg shell.
This leads to decline in birds population. If DDT leaches from the agricultural field, it gets into the water body (the concentration is 0.0003 ppm) and enters the food chain: zooplanktons (0.4ppm)-small fish (0.05ppm)-large fish (2ppm)- any fish eating birds (5ppm). Concentration of DDT increases along the food chain, reaching a high level in the top carnivore bird. DDT concentration disturbs `Ca^(++)` metabolism, egg shells become thin, premature breaking resulting in decline in bird population.
