DDT content in the water of a lake that supplies drinking water to the nearby villages is found to be 0.004 ppm. The pelicans of that area are reported to have 2.6 ppm of DDT. Why has the concentration increased in these birds? What possible harm will this cause to the bird population? Name the phenomenon.

A toxic substance accumulated by an organism can’t be metabolised or excreted, and is thus passed on to the next higher trophic level. This is why the concentration of DDT keeps on increasing at successive trophic levels.

High concentrations of DDT disturb the calcium metabolism in birds. This causes thinning of egg shells and their premature breaking and eventually decline in the bird population.

The process of increase in the concentration of the toxicant at successive trophic levels is called biomagnifications.