Environmental Issues Revision Notes For NEET


        Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water and soil.

        Pollutants are chemical or biological substances that deteriorate our natural environment.

        Primary pollutants are emitted directly from a source, e.g. SO₂, NO₂, CO, etc.

        Secondary pollutants are formed by reaction between primary pollutants in the atmosphere, e.g. O₃, PAN, etc.

        Any undesirable change in the physical, chemical and biological characteristics of air that causes adverse effects on living things is called air pollution. It is mainly caused by combustion of fossil fuels, automobiles, etc.

        Photochemical smog was first reported in los Angeles in 1946. It contains secondary pollutants, e.g. O₃, PAN, etc.

        Air pollution causes fruit damage, leaf damage, chlorosis, etc. In plants. Carbon monoxide combines with haemoglobin and reduces the oxygen carrying capacity of blood.

        Acid rain is caused by oxides of sulphur and nitrogen. The pH of acid rain is less than 5.65.

        Catalytic convertors are fitted into the automobiles exhaust. They have expensive metals (platinum-palladium and rhodium) as the catalyst, that can convert unburnt hydrocarbons into carbon dioxides and water.

        Electrostatic precipitator can remove over 99% particulate matter present in the exhaust from a thermal power plant.

        Water pollution is the contamination of water bodies due to the changes in physical, chemical and biological properties of water that affect the living beings adversely. Sources of water pollution are of two types, i.e. natural sources, anthropogenic or man-made sources. Domestic sewage, industrial waste and agricultural runoff are the main source of water pollution.

        Biochemical oxygen demand (BOD) is the amount of oxygen in mg required to decompose organic matter present in one litre of water. Microorganisms use BOD to decompose organic matter in the water. These consume lot of oxygen and as a result there is a sharp decline in dissolved oxygen in the water body. They can cause death of fishes and aquatic creatures. It is higher in polluted water and lesser in drinking water.

        Eutrophication refers to the ageing of a lake by nutrient enrichment of its water. Nutrient rich in phosphates and nitrogen promote algal growth. Organic matter in water acts as a food source and promotes growth of planktonic algae, called algal bloom. It imparts a distinct colour to the water bodies and causes deterioration of the water quality, fish mortality, etc.

        Biomagnification is the increase in concentration of the toxic substance at successive trophic level, in the food chain. It is indicator of water pollution.

        Ecosan is a sustainable system for handling human excreta by using compositing toilets. It is cost effective also.

        Thermal pollution is warming of an aquatic ecosystem to the point, where desirable organisms are adversely affected. It is caused by the water released from power plants, oil refineries, etc.

        Noise pollution is caused by loud disturbing sounds dumped into the ambient atmosphere. Any value more than 80 dB causes noise pollution. The intensity of sound in normal conversation is 30-60 dB. Hatching of birds is disturbed due to noise pollution.

        Soil pollution is the alternation in soil quality caused by the removal or addition of substance. It is of two types, i.e. negative and positive soil pollution. Soil pollution can be reduced by incineration and pyrolysis.

        Radioactive pollution is physical pollution of air, water and soil due to radioactive materials. Some elements such as radium 224, uranium 235, thorium 232, etc. Naturally emit radiations. Accidental leakage may also cause radioactive pollution.

        Radioactive wastes are released from radioactivity emission of alpha-particles, betta-particles or gamma-rays from nuclides of their elements. Radiation causes mutations very frequently and also increase the chances of cancer.

        Solid wastes are discarded or leftover solid materials. The various wastes are municipal wastes, industrial wastes, mining wastes, hazardous wastes, etc. Solid wastes can be reduced by recovery and recycling, burning and dumping.

        Incineration is controlled aerobic combustion of wastes inside chambers at temperature of 900-1200℃.Pyrolysis is combustion inside chamber in the absence of oxygen.

        Ozone layer depletion is caused by the action of chlorine released from chloroflurocarbons on ozone. Ozone hole particularly marked over Antarctica region.

        Greenhouse effect is the increase in global temperature mainly due to CO₂ concentration. Greenhouse gases like CO₂, CH₄, CFCs, etc. are produced by various human activities.

        Global warming is the gradual increase in average temperature of surface of the earth as a result of increased concentration of greenhouse gases.

        Ozone is found in the upper part of atmosphere. It is continuously formed by the action of UV rays on molecular oxygen.

        Various laws are passed for the environment protection, e.g. Environment act, 1986; Insectiside act, 1968; Air prevention and control of pollution act, 1981, etc.

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