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The most frequently heard of and talked about word, internationally in the present times, is pollution, that is, pollution of the environments: air, water, biosphere and so forth. Ecological crisis or environmental deterioration is one of the most formidable dangers that confront mankind today. Unfortunately, injudicious pursuit for technological and industrial progress by overambitious persons has created multidirectional environmental issues which have brought unforeseen hindrances in efforts towards welfare of mankind. The situation has so much worsened that all living organisms are now exposed to incumbent hazard of pollution of water, air and soil to a greater or less extent. The use of poisonous chemicals in agriculture is increasing uninterruptedly. Large quantities of these and many other chemicals are in use in domestic establishments and industries many of which also release various sorts of waste chemicals as by-products. Accumulation and bio magnification of these pollutants in the biosphere pose a serious problem. The concentration of carbon monoxide, carbon dioxide, oxides of sulphur, nitrogen, and other gases, injurious to the living organisms, is rising in the atmosphere. All these aspects which are linked with environmental degradation due to presence of various pollutants are referred to as environmental toxicology. In the fold of this discipline is the occurrence of incidental exposure of a biological system to chemicals which are basically contaminants of the air, food, and water supplies, and study of causes, conditions and air, food, and water supplies, and study of causes in conditions and effects of such chemicals on a living system and biosphere is included in it. Under this branch are covered studies which involve chemicals intentionally, that is, purposely used on various biological systems either to suppress some kind of life or to achieve certain specific objective responses. By and large, these chemicals are promoted by economic considerations. Both natural chemicals and those which are synthetically manufactured possess the property of selectivity in their action on various living beings. For example, anti-biotics can preferentially harm or kill many bacterial populations while inducing or causing little harm to the organisms in which these bacteria live or thrive.

The use of insecticides and pesticides is based on their selective action which harms the undesirable organisms, leaving economically important species free to grow and multiply. It has been found that a number of chemicals are capable of selectively affecting specific tissues or organs or certain specific functions within the organism. Such chemicals are often used as drugs.

Scientists and technical experts including engineers have realised the severity of the consequences and are now engaged in exerting efforts to make progress in technological and industrial aspects but, at the same time, are applying skill towards ways and means for the abatement of pollution. Now-a-days several national and international agencies are involved with heavy investment of money in project works to control pollution. Endeavour for technological and industrial progress are generally multi-directional. Air pollution is most commonly heard of environmental pollution that has been reported in most industrial towns and metropolis of India and abroad.