Any undesirable changes in our surroundings which are harmful for plants, animals and human beings are known as pollution. Any thing that causes pollution is known as pollutant. Pollutants can be solid, liquid or gas or in the form of noise in an extent greater than tolerable limits prescribed by medical science. Pollution can occur due to human activities and natural events.
Undesirable solid (such as dust, haze, fumes, smoke, smog etc) or gaseous particles (such as oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons and other oxidants.) in the air produce tropospheric pollution. Higher proportion of CO2 in the atmospheric air is the principal cause of global warming. This may ultimately lead to melting of ice in the North and South Pole and over a period of time certain coastal areas may go under water.
A layer of ozone in the stratosphere absorbs about 99.5 per cent of ultraviolet (UV) rays of sun and offers protection to humans and other animals from its harmful effect. Ozone layer is damaged by the effect of certain gases like nitrogen dioxide, methane, chlorine monoxide and CFCs. Environmental scientists working in Antarctica learned about the depletion of ozone layer (ozone hole) over the South Pole. With the depletion of ozone layer, more UV radiation is available to all living beings on earth which causes ageing of skin, cataract, sunburn, skin cancer in humans and damages aquatic life. Quality of plant proteins deteriorates because of undesirable mutation of cells. It enhances the evaporation of water through leaves and decreases the moisture of the soil.
Acid rain is the effect of pollutants. Use of fossil fuels (rich in sulphur and nitrogenous matter) like coal and oil in power stations and furnaces or petrol and diesel in motor engines emit sulphur dioxide and nitrogen oxides, SO2 and NO2 which after oxidation and reaction with water cause acid rain. Many human activities which generate release sulphur and nitrogen oxides are also responsible for acid rains. Ammonium salts are also responsible for creating haze in atmosphere.
Acid rain washes out the nutrients needed for growth of agricultural plantations, trees and plants. Acid rain can precipitate respiratory disorders humans and animals. Acid rain mixes with the rivers, lakes etc. and affects the life of aquatic plants and animals and brings disorder in the ecosystem. It causes corrosion of the pipelines carrying water causing leaching of contaminants into the drinking water. Structures built from stone or metal are degraded by acid rains.
The major effect of pollution which is most visible to common man is the effect of water pollution. The origin of water pollution is human activities. Microorganisms, organic wastes, plant nutrients, toxic heavy metals, sediments, pesticides, chemicals, radioactive substances are the common pollutants found in polluted water. Pollutants reach surface water or ground water through leaking from municipal sewage pipes or deficiency is industrial waste disposal system. Presence of metals in water is detrimental to humans because they cannot be excreted. Over prolonged exposure, they accumulate in kidneys, central nervous system and liver and cause damage to these organs. Wastes from pesticides and dyes manufacturing factories are carcinogenic and capable of casing cancer in the human beings.
Effects of pollution have necessitated the need for judicious use of chemicals in agricultural activities for sustainable development. It has also triggered the need for developing strategies for control of pollution by employing proper system of waste management by reducing the waste as well as adopting proper disposal methods. It has also created a need for recycling of materials and energy. It has given rise to a new branch of chemistry, i.e. green chemistry which utilizes the existing knowledge to reduce the pollution.