Question

(a) What depletes ozone in the stratosphere? How does this affect human life?
(b) Explain the biomagnification of DDT in an aquatic food chain. How does it affect the bird population?

Answer 1

Hint: The Stratospheric ozone is a naturally-occurring gas that filters the sun's ultraviolet radiation. This is typically regarded as the 'good' ozone since it reduces the harmful effects of the ultraviolet radiation. The biomagnification is the buildup of the toxins in a food chain. The DDT concentration is in parts per million. As the trophic level increases in a food chain, the number of toxic build-up increases.

Complete answer: (a) There has been a rise in global temperature in recent times and depletion of the ozone layer is one of the factors behind it. The sun emits different kinds of radiation reaching the earth, mainly containing the Ultraviolet radiation. Too much exposure to these rays can be responsible for the increase in the risk of skin cancer and severely affect the immune system. These rays can even harm single-cell organisms, plants and also aquatic animals. But between the sun’s harmful rays and life on earth, there lies an invisible pale blue thin protective shield known as the Ozone layer or the Ozone shield. Three decades before, scientists discovered that this thin layer is slowly depleting and the reason behind this was certain man-made chemicals like the chlorofluorocarbons and nitrogen oxide, coming out from a wide range of industries and consumer appliances, mainly refrigerators, air-conditioners, fire extinguishers, etc. This chemical reaches the ozone layer and starts destroying it which is popularly known as ‘Ozone hole’. We could not do much about the CFCs that were released already, but still, there is something that we can do now. The first step is to spread awareness about its harmful effects. We can replace all the old air-conditioners and refrigerators that are more than twenty years old with new ones, as it cuts the significant amount of CFCs released into the atmosphere.
(b) Almost all the industrial effluents, hazardous chemicals from hospitals, sewage from homes and many wastes are discharged into the water bodies. The chemical released from these disposal enters the aquatic food chain. The biomagnification refers to the increase in the concentration of these chemicals at each successive trophic level. It mostly occurs with the toxic cannot be metabolized or excreted and hence, get accumulated in the organism and when these organisms are eaten up by other organisms, these chemicals get passed on to them too. At each higher trophic level, its concentration increases and hence, the organism at the top trophic level gets harmed the most. It has a very bad effect on fish-eating birds.

Note: A similar case has been seen in the coastal areas of Japan, where the mercury gets accumulated in fishes and when they are consumed by humans, it causes a serious problem in them which is known as the Minamata disease.