Ozone prevents harmful UV radiations of the Sun from reaching to the earth's surface, thereby it protects life from adverse effects of UV radiations. If ozone is removed completely from the stratosphere, the UV rays will reach to the earth and will lead to several diseases like sunburn, skin infection etc.

(i) Tetrachloroethene, CI₂C = CCI₂ is suspected to be carcinogenic and also contaminates the ground water. This harmful effect will be prevented by using liquefied CO₂ along with suitable detergent
(ii) Use of liquefied CO₂ along with detergent will not be completely safe because most of the detergents are non-biodegradable and they cause water pollution. Moreover, liquefied CO₂ will ultimately enter into the atmosphere and contribute to the green house effect.

If domestic waste in a city is not properly managed, it may finds its way into sewers or may be eaten up by the cattle. The non-biodegradable waste like polythene bags, metal scrap etc., choke the sewers. The polythene bags if swallowed by the cattle can result into their death. Similarly, if industrial waste is not properly managed, it will cause pollution of the air, soil and water.

Pesticides from the soil are transferred into the crops and from the crops these are transferred into fish food. through the run-off water from fields and enter the bodies of fishes. Therefore, pesticides are transferred from lower trophic level to higher trophic level through food chain. Over the time, the concentration of pesticides in fishes reach a level which causes serious metabolic and physiological disorders.

The processes which are responsible for the reduction of dissolved oxygen in water are excessive use of phosphatic and nitrate fertilisers, detergents, the discharge of human sewage and organic waste from food, paper and pulp industries. The microorganisms which oxidise organic matter also use oxygen dissolved in water. Moreover, during night, photosynthesis stops bu the aquatic plants continue to respire, resulting in reduction of dissolved oxygen.