Question

In an area where DDT had been used extensively, the population of birds reduced significantly because

• A. Birds stopped laying eggs
• B. Earthworms in the area got eradicated
• C. Cobras were feeding exclusively on birds
• D. Many of the birds' eggs laid, did not hatch

Answer 1

The correct option is D Many of the birds' eggs laid, did not hatch

Biomagnification refers to an increase in concentration of a toxicant at successively higher trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted and is thus, passed on in the food chain. DDT biomagnification occurs in aquatic food chains. If the concentration of DDT in water for instance, is 0.003 ppb (ppb = parts per billion) in water, that ultimately reaches 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification. High concentration of DDT disturbs calcium metabolism in birds which causes thinning of egg shells and their premature breaking.