Today millions of people are without basic needs of cloth, shelter, health, education and employment. This is not due to overpopulation alone but also due to environmental consequences. The loss of forests, fertility of soil, productivity and energy crisis have created many problems. The pollution created by industries, technology etc. and over-consumption by the affluent society lead to the rapid depletion of basic natural resources. Many human problems are also due to mismanagement of environment which is created by man himself.
Environmental implications due to pollution are in various aspects. These produce serious problem for human beings to maintain its existence, protection, survival and for the improvement of general standard. The basic needs of human beings have disturbed natural resources and finally led to a situation which has threatened to be disastrous.
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In the recent years everyone has started thinking over the problem of over-population and its consequences, which is primarily concerned with the environmental pollution and every effort should be made to focus public attention to save mankind from self destruction and steps should be taken at national and international levels so that the consequences may not become worse.
The ecological state of biosphere is becoming more and more dis-balanced day by day due to technical and industrial advancements as well as population explosion. Vast changes are taking place in the environment due to interaction between human society and environment itself. Man is exploiting the natural resources for its own interest and many such instances are there as clearly indicate that man has disturbed the natural balance for the sake of small benefits and has changed the environment of many places to such an extent that they are not fit for inhabitation by living beings.
The environmental science is concerned with the study of all the systems of air, land, water, energy and life that surround us. Environmental problems are so diverse and diffused that virtually every activity of civilization interacts with the environment. The addition of extraneous materials or energy in a particular environment in concentrations greater than the normal renders the environment partially or wholly un-favourable for human life.
This is referred to as environmental pollution. “Environmental pollution is the un-favourable alteration of our surrounding, wholly or largely as by-products of man’s action through direct or indirect effects of changes in energy patterns, radiation levels, chemical and physical constitutions and abundance of organisms”. These changes may affect man directly or through his supplies, of water and agricultural and other biological products, his physical objects or possessions, or his opportunities for recreation and appreciation in nature—from U.S. Products Science Advisory Committee, Environmental Pollution Panel (1965)
Pollution and contamination are two terms sometimes used interchangeably. Contamination is the presence of harmful substances or organisms that may cause diseases or discomfort to human beings. Polluted material need not necessarily be contaminated. Dependent as he is on air, water and food from environment, man is the main culprit in polluting these natural resources to the point of no return.
Pollution is defined as the addition of extraneous materials to water, air or land which adversely affect the natural quality of the environment. In some cases, it may involve the removal, rather than addition, of constituents from the environment. A pollutant is a substance which may alter environmental constituents or cause a pollution. A pollutant can also be defined as constituent in the wrong amount at the wrong place or at the wrong time. For example, nitrogen, phosphorus and potassium are extensively used in agriculture to increase crop yields but sometimes they cause pollution of lakes and rivers by promoting algal growth.
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The natural sources of pollution are, no doubt, important on a global scale man generated pollutants may be more important in urban and industrial areas where the adverse effects of pollution are most severe. There is accumulating evidence that many types of pollutants can be distributed over the whole earth in relatively short period of time. Radioactive fallout from atmospheric nuclear explosion test is detectable throughout the world within a few days ‘or weeks; not even the polar regions are immune from fallout.
Comfort giving automobile’s are polluting the atmosphere with oxides of C, N, and other noxious gases. Coal, diesel oil and other fossil fuels are emitting suffocating SO2 and choking our lives. Synthetic chemicals like plastics are adding to the problem of solid waste disposal; while detergents that cannot be decomposed by micro-organisms are making the natural rivers and streams polluted bubble boxes. Some other effects of environmental pollution are problems of health, soil erosion, sanitation, water supply, energy crisis, population and depletion of natural resources.
The law of conservation of mass or material equally applies to the pollutants and while one cannot destroy them, they may be changed from one state to another or from one compound to a another. The presence of small amount of pollutants may make profound influence on human health even when the level of air pollutants is so low that they cannot be detected except with special instruments. Some pollutants may harm living creatures exposed for long periods of time.
Pollutants are divided into two categories:
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(i) Biodegradable pollutants:
These pollutants are natural organic compounds which are degraded by biological or microbial action sewage.
(ii) Non-biodegradable pollutants:
These are not acted upon by microbes but are oxidized and dissociated automatically.
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They are further divided into two classes:
(a) Wastes e.g., glass, plastics, phenolics, aluminium cans, etc.
(b) Poisons e.g., radioactive substances, pesticides, heavy metals like mercury, lead, cadmium etc.
As regards the nature of pollutants, the problem of pollution can be divided into the following categories:
1. Pollution caused by solid wastes
2. Pollution caused by liquid wastes
3. Pollution caused by gaseous wastes
4. Pollution caused by wastes without weights.
1. Pollution caused by solid wastes:
Solid wastes are useless and unwanted substances that are discarded by human society. Solid wastes include the heterogeneous mass of urban wastes as well as the more homogenous accumulation of agricultural, industrial and mining wastes. The proportions of different constituents of solid wastes vary from season to season, place to place, extent of industrial and commercial activities and so on.
1. Urban solid wastes are those which are collected and disposed of by municipal bodies. These include the following:
(i) Garbage such as wastes from kitchen, slaughter houses, canning and freezing industries.
(ii) Rubbish including the combustible wastes such as leaves, grasses, plants from the gardens, clothes, paper etc. and noncombustible wastes such as bottles, crockery and plastic materials, glass, metals etc., generated from households, commercial establishments and markets.
(iii) Ashes.
(iv) Wastes formed due to demolition and construction processes, as for example, bricks, stones, plaster, plastic materials, furniture’s etc.
(v) Dead animals.
(vi) Sludge, settled solid components of sewage wastes.
2. Agricultural Solid Wastes:
Agricultural Solid Wastes such as manure, crop residues, pesticides, insecticides, wastes of farm animals and so on.
3. Mining Wastes:
Mining Wastes such as wastes from coal mines, mines of metal ores, radioactive substances etc.
4. Industrial Solid Wastes (ISW):
These are generated by various industrial units such as chemical plants, paint industries, cement plants, metallurgical plants, power plants etc.
Industrial solid wastes can be broadly classified into the following two groups:
(i) Non-hazardous wastes.
(ii) Hazardous wastes.
Non-Hazardous Industrial Solid Wastes:
The major industries in urban areas that generate substantial amount of non-hazardous solid wastes are fruit and food processing plants, cotton mills, paper mills, sugar mills, textile mills etc. The wastes generated from these industries are biodegradable. Non-hazardous non-biodegradable solid wastes are coal ash or fly ash generated by thermal power plants, blast furnace slags, wastes of steel melting units, muds etc.
Hazardous Industrial Solid Wastes:
Some of solid wastes generated by industries are inflammable, corrosive, explosive, chemically highly reactive and toxic. The major industries that produce hazardous wastes are metal, chemical, drug or pharmaceutical, leather, pulp and paper, electroplating, refining, pesticide, dye, rubber etc. It is estimated that currently the industrial sector generates about 100 million tonnes of non- hazardous solid wastes and two million tonnes of hazardous wastes a year.
The surveys conducted by Environment Protection Training and Research Institute from 1971 to 1995 revealed that the urban population generated 375 g. of solid wastes per head per day in 1971 and in 1995 it was estimated to be 490 g. per head per day (Table 13.1). 
The problem of domestic solid waste whether it is garbage, litter or rubbish cannot be underestimated. In advanced countries it is estimated that at an average a city dweller produces more than half a ton of garbage per year.
2. Pollution caused by liquid wastes:
Major portion of water on the surface of earth is not in a form that can be used for domestic purposes by man since it is saline Man obtains fresh water from the well known hydrologic cycle. Surface runoff gathers minerals and organic impurities as it moves down to the sea. Under normal conditions river takes care of many polluting substances that enter its body. Green plants and algae take up CO2 from water and in presence of sunlight synthesize carbohydrates and O2 is produced by splitting of water molecules. Animals take up O2 and give up CO2 and other compounds which are used by the plants.
This is ecological balance in a natural stream. If some organic matters, that can be food materials for bacteria, enter water course then bacteria oxidize these materials and in that process take up O2 from water. If the process of re-oxygenation is slower than the process of de-oxygenation then river will be devoid of life sustaining dissolved oxygen and aquatic animals and plants will die and under anaerobic condition foul smelling hydrogen sulphide and other products are formed. The river can be termed dead in the sense that it cannot sustain normal aquatic life.
Sewage:
The important source of organic pollutants is sewage which contains faecal matter, urine, and kitchen washings and some soil washing. Sewage contains large number of bacteria! both pathogenic and harmless. The strength of organic waste materials of sewage is measured in terms of demand for dissolved oxygen required in oxidation of organic matter by microorganisms.
This value is expressed in terms of mg of O2 per litre of waste. Since biological reaction is dependent on time and temperature, this O2 demand (called biochemical O2 demand or B.O.D.) is given for 5 days at 20°C. If the value of B.O.D. is below 1500 mg per litre, the sewage is termed weak waste, if it is below 4000 mg per litre it is medium an above this value it is termed strong waste.
Domestic sewage in small quantities rarely gives trouble. However, if liquid industrial wastes enter the river along with acid or alkali and poisonous substances like cyanides, etc., the aquatic life in the river is affected and self-purification system of water is impaired.
Surface run-off from agricultural fields can carry nitrogen and phosphate fertilizers that enter the aquatic environment and later undergo decomposition adding to the organic loading of the stream. Pesticides, and herbicides which enter waters may kill some organisms or accumulate in the fishes which when consumed by man, pass on the chemicals giving rise to cumulative poisoning.
3. Pollution from gaseous wastes:
The gaseous wastes—most dangerous to people—are the ones that threaten the life of animals and plants. Carbon monoxide, SO2, NO2 (nitrogen dioxide), ozone and the so called “smog gases” made up of complex mixtures of hydrocarbons are common gaseous pollutants. These are the gases generally found in the atmosphere of industrial cities.
Carbon monoxide which is a product of incomplete combustion is deadly poisonous at high concentration. It has high affinity for haemoglobin in the blood and prevents that from transporting oxygen from the lungs to the tissue of the body. Fortunately, most of the times the amount of CO in the open air is too low to do much damage to human health.
Hydrogen sulphide is another deadly gas when it occurs in large concentration which is rare.
Sulphur dioxide of the common gaseous pollutants, (Sulphur-di-oxide SO2) is regarded as one of the most dangerous gases to human health. It attacks the respiratory tracts and interferes in the breathing mechanism. Concentrations above 1 ppm (part per million) can begin to affect people.
Nitrogen dioxide gas in sufficient quantities in air may attack lungs and cause eye irritation. Some hydrocarbons and nitrogen dioxide under the influence of sunlight produce complex substances affecting the eyes and mucous membrane.
Smog is the result of fog and the photochemical oxidation products of hydrocarbons and other organic compounds released from automobile exhaust.
4. Pollution caused by wastes without weight:
The fourth kind of pollution caused by “wastes without weight” can also be called pollution by energy waste. Certain types of pollution cannot be seen and these are included in this group.
Wastes without weight include the following:
(a) Radioactive substances and lethal radiations.
(b) Heat, and
(c) Noise.
(a) Radioactive substances:
The amount of radioactivity in this atomic age has increased in the environment many folds as compared to Thirties and Forties. According to one authority, man may be already having radioactive cesium in his muscles, radioactive strontium in his bones and radioactive iodine in his thyroid indicating the extent of radioactive pollution. Although every precaution is taken in the functioning and maintenance of nuclear reactors, it has been shown that minute yet measurable amount of radioactive waste material escapes into the environment.
From the mining operation of uranium to the use and final disposal of wastes from the reactors radioactive waste materials continuously escape out. Besides emission from nuclear installations there is worldwide fallout of radioactive substances from atomic explosions. This kind of radioactive pollution caused alarm in the late Fifties and Sixties leading to a moratonum on surface and aerial tests explosions by the super powers. China and France incidentally continue to make occasional tests.
The underground storage of radioactive material in concrete or steel containers still does not ensure complete safety. Radioactivity cannot be destroyed and hence it has cumulative effect. The minute radioactive atoms, molecules or ions in water to which they may have leaked out pass on to aquatic organisms and since they are part of food chain, the radioactivity goes on accumulating in the higher organisms.
In a survey of Columbia river into which cooling water of Plutonium producing reactors was dumped, it was estimated that compared to the radioactivity of river water the microscopic plants and animals had one thousand times more radioactivity, fly larvae had 35,000 times more radioactivity, while the eggs of ducks which fed on the larvae etc., had 40,000 times and some birds had almost 75,000 times more radioactivity than that of water.
(b) Heat:
A large quantity of waste heat energy by way of hot liquid streams or hot gases released by industries, automobiles etc., dissipates in to atmosphere and water and enhances the temperature.
(c) Noise:
Noise is unwanted sound. It has come to be regarded as an important pollutant of the environment. The sources of noise for the general public are the machine in the industry, traffic noise due to trucks and cars as well as due to the indiscriminate use of transistors, radios and public address systems. Processions, public broadcasting of films, music of high pitch on festive occasions are the noises that pollute the environment. Noise produced from the aircraft, especially the supersonic jets, is harmful.