Question

Thermal pollution of water bodies is due to
A. Discharge of heat (hot water) from power plants
B. Discharge of chemicals from industries
C. Discharge of waste from mining
D. Discharge of agricultural run off

Answer 1

Hint: Pollution is the harmful changes in the normal existing environmental conditions. Pollutants or the pollution causing agents are responsible for alteration of several properties of water bodies such as temperature. The normal temperatures of the water bodies are maintained within an approximate level which remains ambient for the growing flora and fauna.

Complete answer:
Thermal pollution can be defined as the undo changes in the quality of water by any process due to changes in the ambient water temperature. The changes in the temperature may be the result of heat. Heat is the major pollutant that causes temperature changes in the water bodies and it leads to thermal pollution.
The main reason of thermal pollution is the heating of the water bodies due to discharges from power plants as hot waters. Industrial effluents which are the result of anthropogenic activities of humans are also responsible for increasing the water temperature and leading to thermal pollution.
Heat discharges into a waterbody directly influences the ecological balance in that system. The abrupt heating or hot water deplete the oxygen concentration and lowers the solubility of oxygen in water. It also affects the activity of the aerobic decomposers due to oxygen depletion which further affects the nutritional supply in the water bodies. In other words, the productivity of the water bodies is affected and adversely harms the living communities.
Chemicals that are discharged from the industries are a harmful source of pollution but are not direct sources of thermal pollution. When the chemicals enter the water bodies, they cause harmful chemical alteration in the physico chemical balance of the water bodies. They may also increase the temperature through several types of secondary reactions.
Mining waste brings about several changes in the quality of water and causes it unfit for human use or development of aquatic organisms. However, mining wastes are directly related to thermal pollution.
Several types of pesticides and insecticides which are used in agricultural practices enter the water bodies and are responsible for alteration of the water quality. They do not change the water temperature but they alter other physio-chemical properties of water.

Hence, the correct answer is option (A).

Note: The pollution causing agents or material that enter the water bodies and cause changes in the normal temperature or elevate the normal temperature is known as thermal pollution. The thermal pollution of water bodies is mostly caused by the hot water or discharge of heat (hot water) from power plants and related industries.