4. Write critical notes on the following:
(b) Biological magnification
Biological magnification- It refers to the increase in the concentration of a persistent chemical with the rise in trophic level. The chemical becomes hazardous when its concentration becomes very high. For example, a DDT concentration of 0.003 ppb becomes 0.003 ppm in phytoplankton, 0.04 ppm in zooplankton, 0.5 ppm in small fish, 2.0 ppm in larger fish and 5 ppm in fish-eating birds.