Essay on Water Pollution for Students

Essay on Water Pollution! Learn about: 1. Essay on Ground Water Pollution 2. Essay on Surface Water Pollution 3. Essay on Lake Water Pollution 4. Essay on River Water Pollution 5. Essay on Sea Water Pollution 6. Essay on Domestic Water Pollution 7. Essay on Industrial Water Pollution 8. Essay on Agricultural Water Pollution 9. Essay on Solid Waste Pollution 10. Essay on Thermal Pollution 11. Oil Pollution.

Essay on Water Pollution for Students

Essay Contents:

  1. Essay on Ground Water Pollution
  2. Essay on Surface Water Pollution
  3. Essay on Lake Water Pollution
  4. Essay on River Water Pollution
  5. Essay on Sea Water Pollution
  6. Essay on Domestic Water Pollution
  7. Essay on Industrial Water Pollution
  8. Essay on Agricultural Water Pollution
  9. Essay on Solid Waste Pollution
  10. Essay on Thermal Pollution
  11. Essay on Oil Pollution


  1. Essay on Ground Water Pollution for students:

Today human activities are constantly adding industrial, domestic and agricultural wastes to ground water reservoirs at an alarming rate. Ground water contamination is generally irreversible i.e. once it is contaminated; it is difficult to restore the original water quality of the aquifer. Excessive mineralisation of ground water degrades water quality producing an objectionable taste, odour and excessive hardness.

Although the soil mantle through which water passes acts as an adsorbent retaining a large part of colloidal and soluble ions with its cation exchange capacity, but ground water is not completely free from the menace of chronic pollution.


We have long believed that ground water in general is quite pure and safe to drink. Therefore, it may be alarming for some people to learn that groundwater infact may easily be polluted by any one of the following sources. Problem of groundwater pollution can be understood by two examples i.e. Love Canal episode (1976-77) and arsenic poisoning in West Bengal (India).

In most of the cases the quality of groundwater is good and it can be safely used without any elaborate treatment, because the water before getting stored in the groundwater reservoir, undergoes natural filtration during percolation through the soil pores. Further the groundwater is generally free from suspended impurities and organic matters which are responsible for the development of disease producing bacteria.

The groundwater is therefore less likely to be contaminated by bacteria. In some cases depending on the characteristics of the geological formations with which the water comes in contact, the groundwater may contain large amount of dissolved salts, minerals, gases, etc., which may impart different taste, odour, and certain properties such as hardness etc., to the water. However, the quality of groundwater may be considerably deteriorated if it gets polluted.

The various causes of groundwater pollution and consequent deterioration of its quality are as indicated below:

1. The groundwater may get polluted on account of infiltration and percolation of-

(i) Domestic and municipal sewage from septic tanks, waste water disposal ponds, etc.

(ii) Industrial wastes;

(iii) Organic wastes from food processing, industries, lumber processing industries, etc.

(iv) Mineral wastes from metal processing industries, mining and ore extraction industries, etc.;

(v) Wastes from oil industries, chemical industries, etc.

(vi) Rain falling on sanitary land fills (i.e., dumping ground for solid and semi­solid refuses), chemical land fills (i.e., dumping ground for solid and semi­solid waste from chemical industries), etc.;

2. The quality of ground water may get degraded due to-

(i) Infiltration and percolation of irrigation return water contaminated with dissolved fertilizers and disinfectants used for cultivation;

(ii) Interchange between aquifers due to improperly constructed, defective or abandoned wells;

(iii) Interchange between aquifers due to differentials in pressure levels resulting from excessive withdrawal;

(iv) Overdraft conditions, i.e., withdrawal far in excess of the quantity of water recharged or recouped;

(v) Sea water intrusion into the aquifer;

(vi) Upward or lateral diffusion of connate brines and/or juvenile water due to over pumping;

(vii) Contamination from the dirty surface water, (resulting from washing of clothes, utensils, etc., at or near the wells) entering the improperly constructed wells;

(viii) Inflow and/or percolation of juvenile water from highly mineralized springs and streams;

(ix) Mineralization resulting from plant transpiration and/or evaporation.

Measures to Control Groundwater Pollution:

The most important measure which may be adopted to control groundwater pollution is to locate the well in such a way that the minimum distances from the well to the possible sources of pollution are great enough to provide reasonable assurance that subsurface flow or seepage of contaminated water will not reach the well. The following minimum distances are recommended to be kept between the well and the possible source of pollution.

A well should be at least:

1. 45.7 m (150 feet) from a storage area of spray materials, commercial fertilizers or chemicals that may cause contamination of the soil or groundwater.

2. 30.5 m (100 feet) from a low grade manure storage area.

3. 22.9 m (75 feet) from cess pools (pools in which filthy water collects), leaching pits and dry wells.

4. 15.2 m (50 feet) from a buried sewer, septic tank, subsurface disposal field, grave, animal or poultry yard or building, privy or other contaminants that may drain into the soil. Recent research has, however, shown that the distance between a septic tank, leach field and a down gradient well should be greater than 30.5 m (100 feet) if the soil is coarser than fine sand and the groundwater flow rate is greater than 0.01 m/day (0.03 feet/day).

5. 6.1m (20 feet) from a buried sewer constructed of cast iron pipe or plastic pipe with tested water tight joints, a pit or unfilled space below ground surface, petroleum storage tank, a water tight tank which receives sewage or liquid waste.

6. Wells with casings less than 15.2 m (50 feet) depth and encountering less than 3 m (10 feet) of impervious material must be located at least 45.7 m (150 feet) from cess pools, leaching pits or dry wells and at least 30.5 m (100 feet) from subsurface disposal fields, manure storage piles or similar sources of contamination.

The other measures which may be adopted to avoid the pollution of ground water are as indicated below:

1. The top of the well should be properly covered to prevent the entry of surface water into the well. The ground must slope away from the well.

2. The washing of clothes, utensils, etc., at or near the well should not be allowed.

3. The pumping rate from the well should be normal and not excessive.

4. No trees should be allowed to be grown over or near the well since the fallen leaves etc., may cause the contamination of the well water.

5. In the case of drilled wells, the annular space between the well hole and casing should be filled up by cement grout to a depth of at least 3 m.

6. The casing should extend by about 3 m below the water table.

7. The priming of pump should not be carried out by using contaminated or unsafe water.

8. The pump house should be adequately drained and it should be protected against flooding.

9. The pumps should not be installed below ground in pits.

10. The connection between casing and pumping unit should be water tight.

11. The wells should be provided with enough vents so as to prevent the suction of contaminated water into the wells.

2. Short Essay on Surface Water Pollution:

Surface water pollution should be free from the following contaminants:

(i) Compounds which impart colour, odour and turbidity e.g. oils, greases, phenols, toxic metals and organics etc.

(ii) Substances which may precipitate to form objectionable deposits or float on the surface as oil, scum or debris.

(iii) Toxic radionuclides which acutely affect the physiology of men, animals and aquatic organisms.

(iv) Substances which are likely to result in enhancing the growth of undesirable aquatic life.

(v) Heavy materials that check the growth of aquatic flora and fauna.

(vi) Thermal effluents should not increase the water temperature by 3 to 5°F.

(vii) Chlorinated compounds, chloroform and chloramines used during chlorination of surface water should not exceed the permissible dose (1000 ppb.) fixed by ‘EPA’.

(viii) Ozonisation instead of chlorination of water should be applied as in France and Switzerland. However, the method is rather expensive and ozone rapidly converts to oxygen. 

Factors Affecting Surface Water:

The nature and extent of surface water pollution depends on following factors:

(i) Hydrological characteristics of diluting biocides and the extent of self-purification.

(ii) Vegetation, soil type and degree of weathering rocks.

(iii) Wastewater disposal systems and techniques for treatment of domestic and urban sewage including pretreatment of industrial wastewaters.

(iv) Physical, chemical and biological characteristics of waste water entering the surface waters.

(v) Hygienic and health situation of the communities residing near surface waters.

Sources of Surface Water Pollution:

Surface water comes in direct contact with the atmosphere, seasonal, streams, rivulets and surface drains. So there occurs a continuous exchange of dissolved and atmospheric gases while the wastes are added through water conveyances.

The chief sources of surface water pollution are as follows:

(i) Sewage and waste

(ii) Infectious agents

(iii) Particulate soil and mineral matters

(iv) Dissolved toxic pollutants,

(v) Mineral and chemical compounds

(vi) Radioactive nuclides

(vii) Thermal pollutants

(viii) Organic chemical exotics.

Generally surface waters near the cities and industrial complexes where the atmosphere is contaminated by CO2, CO, SO2, NH3, NOx, H2S, factory smoke and vehicular exhaust are more polluted water than those of rural areas. In flowing polluted water, the DO content varies with the distance and depth. Generally oxygen solubility in distilled water is 9.1 mg/l which decreases with increase of temperature.

In polluted surface waters, the ions like Na+, K+, Mg2+, SO42 H2PO4 and H4P2O72interact again forming a variety of complexes, thereby deteriorating the quality of surface water. Chemical processes like ion exchange, chelation, precipitation, coagulation, aggregation, oxidation, reduction and dissolution are operating simultaneously making the polluted water an extremely complex system. 

Factors Affecting Nutrient Loss in Surface Water:

Polluted surface water is highly degraded and contains much less nutrient content.

Main factors affecting nutrient loss in water are as follows:

(i) Irrigation practices

(ii) Rainfall patterns

(iii) Topography

(iv) Temperature and evaporation

(v) Soil erosion, sedimentation and siltation

(vi) Nature of vegetation cover

(vii) Soil conservation practices

(viii) Amount of run-off and percolation

(ix) Hydrological features of the sea.

Processes Aggravating the Pollution Problems in Water:

The surface and ground water pollution is complex due to numerous processes which occur simultaneously in nature as:

(i) Nature of industrial effluents.

(ii) Naturally occurring radionuclides in water.

(iii) Chemical chain of reactions occurring in water.

(iv) Variation in the rate of flow of water.

(v) Toxic resulting products in water.

(vi) Biological activities of aquatic flora and fauna.

(vii) Extent of water quality modification with time and space.

Water Pollution is More Complex than Air Pollution:

Water pollution is more dangerous and critical than air pollution due to the following reasons:

(i) Sources of water contaminants being more diverse.

(ii) Slower rate of self-purification.

(iii) Contamination of water is more sensitive to propagation of life as compared to air.

Protection of Surface Water from Pollution:

Water is an indispensable need of life. It is therefore extremely necessary to develop a suitable technology to protect, at least, the quality of drinking water not only against biological hazardous pollutants and biodegradable organics but also against toxic inorganic complexes and non-biodegradable wastes. Hence the whole water system should be examined as a whole and then to develop an efficient workable model to preserve and maintain best quality of surface water.


Essay on Lake Water Pollution

Essay on Lake Water Pollution

3. Essay on Lake Water Pollution for Class 5 Students:

In India, coastal lakes and estuaries cover about 2.6 million hectares of water area. The rapid pace of industrialisation and urbanisation has posed a serious threat to these vast varieties of water resources.

Following sources are responsible for pollution in lake water:

Sources of Pollutants in Lake Water:

(i) The discharge of organic wastes from hills and toxic effluents from urban areas has polluted the lakes to such an extent that fish mortality is raised from 80,000 to 100,000 per year.

(ii) Waste sludges from factories as well as washings and dumping of tailings constitute the important sources of lake water pollution.

(iii) Sewage treatment plants also contribute to toxic organic matters in the lake water.

(iv) Toxic and hazardous effluents from industries pose serious pollution of lake water which decreases the lake population considerably.

(v) Siltation of lakes due to dumping of enormous quantities of sediments is the major source of lake water pollution.

(vi) Surface run off, rivulets and streams bring inorganic nutrients from agricultural lands into lakes. These effluents consist of excessive concentration of nitrates and phosphates causing well known lake eutrophication disrupting the whole aquatic environment.

4. Essay on River Water Pollution :

Today pollution of water resources have been most exploited due to increasing population, industrialisation, urbanisation, increasing living standards and broad spheres of human activities.

Major Indian rivers, such as Ganga, Yamuna, Tapti, Narmada, Sone, Chambal, Daha, Damodar, Krishna, Cauvery, Brahmaputra, Mahi and other rivers are severely polluted.

The following important conclusions were drawn from the river water pollution:

(i) Water quality is deteriorated everywhere.

(ii) Rivers were severely polluted during the monsoon periods and minimum during the winter.

(iii) The effect of effluents and discharge varies with the distance and nature.

(iv) Damodar River (River of sorrow) is extremely polluted. Chambal River is extremely polluted up to 32 kms.

(v) Water resources contain toxic metals such as As, Hg and other chemicals such as ammonia, cyanide, organic matter etc. in different concentration.

(vi) Suspended solids, odour and turbidity get increased abruptly in rainy seasons.

(vii) Coliform content also increases upto 100 fold in the river water during monsoon.

5. Essay on Sea Water Pollution:

Oceans are the major source of water supply in the world. More than 70% of the earth’s surface is covered by water bodies. Within this vast liquid expanse lie inexhaustible amount of food, mineral, energy, salinity gradients besides coal, oil and gas. Compelled by the impending depletion of land resources, man looks to the sea in a frantic search for more and more resources to meet the increasing demand of population.

In this pursuit man is prone to destroy the aquatic environment either by mismanaging or by over exploitation. Man’s activities are largely responsible for measurable and detrimental effects on the aquatic environment. Oil pollution in the sea appears to be the main factor which poses serious threat to the marine ecosystem and fisheries of the world. Now the oil pollution of harbours, bays, rivers, beaches and open oceans has been increasing tremendously every day.

Marine pollution is defined as the discharge of waste substances into the sea resulting in harm to living resources, hazards to human health, hindrance to fishery and impairment of quality for use of sea water. Marine pollution is associated with the changes in physical, chemical and biological conditions of the sea water. This water is also unfit for human consumption and industrial purposes because of high salt content. Chemically it is a solution of 0.5 m NaCl and 0.005 m MgSO4 containing traces of all conceivable matter in the universe.

Like the land, the air, the rivers, the lakes, our seas and oceans also suffer from pollution. One of the commonest pollutants of the sea is raw or treated sewage. It is interesting to note that in reasonable quantities sewage can be harmless or even beneficial. For example, nitrates and phosphates in sewage fertilise sea water, leading to increase in the growth of microscopic plant life, phytoplankton in the sea. This acts as a food for minute animals which in their turn, end up as food for fish and large sea animals.

On the other hand, overburden of nutrients gives rise to eutrophication. The excessive nutrients lead to prolific breeding of the minute plants near the sea surface. This algal bloom prevents the sunlight from reaching deep in the sea. As a result, photosynthesis is either reduced or stopped.

The plants start taking in oxygen and giving out CO2, thus using up more oxygen. Thus they die in large numbers and are decomposed by bacteria, further decreasing the oxygen content. As a result, fish which requires about 3 mg of dissolved oxygen per litre of water, and other animals start to die.

Organic pollution also causes the excessive multiplication of harmful organisms, such as dinoflagellates, which sometimes give water a red tinge. The resulting red tides lead to large scale mortality of fish or they may be eaten up by fish. When such fish are consumed by man it results in severe poisoning, ciguatera or even death.

Another rich sources of phosphorus are the synthetic detergents which have widely been used now as a replacement of soap. Sodium tripolyphosphate, Na5P3O10 (STP) used as filler adjusts pH to make the water alkaline and soften hard water. It has now been replaced by trisodium nitrilotriacetate (NTA) which is biodegradable, but capable of forming complexes with Hg, Pb, Cd and As.

Another source of nuisance is the foaming agent used in synthetic detergents. The danger of sewage lies in harmful bacteria which cause typhoid, dysentery, diarrhoea, cholera and other diseases. While these cannot survive long in sea water, they may be taken by animals such as oysters and clams. Once these harmful germs get into these filter feeders, they live inside them. If these oysters or clams are eaten without sufficiently cooking to destroy the germs, we may also suffer diseases.

Serious pollution occurs when sewage contains man-made chemicals such as pesticides, fertilisers or heavy metals. DDT, banned in developed countries, is still used in developing countries. It tends to get more and more concentrated as one moves up in the food chain.

Thus fish, growing in sea water with 0.1 part of DDT per billion parts of water will have about 57 mg of DDT per kg body weight. It increases to 800 mg per kg for sea gulls which feed on these fish. DDT is known to affect calcium metabolism. As a result, sea gulls lay eggs with thin shells, which break down when the mother birds sit on them and no baby gulls are hatched.

6. Essay on Domestic Water Pollution:

It includes waste water from homes and commercial esta­blishments. Domestic waste water arises from many small sources spread over a fairly wide area but is transmitted by sewers to a municipal waste treatment plant.

Generally, the impurities in domestic wastes get diluted and seldom total more than 0.1% of the total mass. This material has been largely organic and gets oxidized by bacterial decom­position to nitrate, phosphate, carbon dioxide, and water. As this type of decomposition needs the use of dissolved oxygen, it places an oxygen demand on the system. Because of this tendency to remove oxygen in the decomposition process, a common indicator used to monitor this type of input in receiving water has been the BOD (Biological Oxygen Demand) Test.

In this analysis, the amount of oxygen for decomposition is measured over a 5-day period. In systems receiving significant amount of organic material, the bacterial decomposition will remove large amounts of dissolved oxygen, which causes oxygen depletion. These systems are considered to have a high BOD. Conversely, when the input of contaminants in absent or mini­mal, the oxygen levels will not be drastically reduced because the bacteria will not need an excessive-amount of oxygen to decompose small amounts of materials. In these cases there would be a low BOD on the system.

Domestic water requirements differ from season to season and from rural to urban areas. We use more water in summer than winter. Water consumption in cities is greater than rural areas. Factors like standard of living and habits of the people determine the per capita use of water.

In India the per capita consumption of water in both rural and urban areas is generally not known because citizens in addition to municipal supplies do use private wells, rivers and lakes for their water demands. Per capita consumption of water has been assumed to increase with the standard of living however, water services are available only for 2 to 3 hours per day. As a result per capita water use has declined in many cities due to tremendous growth in their population.

The starting point of domestic water pollution is urbanization. It is rapidly progressing throughout the world. Urban waters often have elevated nutrient levels, especially phosphorus. Many urban water surfaces are covered with a thin film of oil and grease. In a planned city the run off is channeled into two ways.

In the first, storm and domestic sewers are separate systems. In the second, storm and domestic sewers are combined. The leakage of sewers is very common in big cities. The consumption of this water by poor people specially those living in slums close to sewers leads to diseases that often take the shape of an epidemic.

Domestic water pollution is mainly caused by sewage. Sewage is defined as the water-borne waste derived from home, animal or food processing plants and includes human excreta, soaps, organic materials, different types of solids, waste food, oil detergents, paper and cloth. They are the largest group of water pollutants.

Water pollution is caused by uncontrolled dumping of waste collected from villages, towns and cities into ponds, streams, lakes and rivers. A major ingredient of most detergents is phosphate. Phosphates support luxurious growth of algae. Algae withdraw large quantities of oxygen from water. It becomes detrimental to other organisms. Domestic waters are the primary sources of water pollution. The domestic sewage contributes to the largest amount of waste and it has been estimated that approximately 20,000 million litres per day reach the coastal environment of the country.

Bombay has the capacity to treat only 390 mid against 1200 mid of domestic sewage. Due to such partial sewage treatment, waste water retains the original characteristics: that result into severe damage to water quality.

The huge discharge of sewage allows following events that lead to water pollution:

i. Depletion of Oxygen Contents:

The aerobic bacteria present in water are responsible for the decomposition of organic matter. The quantity of oxygen utilized by the bacteria for the degradation of organic substance is called biological oxygen demand (BOD). Thus BOD value can be used as an indicator of water pollution. Alongwith BOD, the quantity of oxygen dissolved in a water body (DO), indicates the quality of bio-life in a water system. DO below 4 to 5 ppm is detrimental to the system.

ii. Promotion of Algal Growth:

Stimulation of heavy algal growth and shift in the algal flora to the blue green algae, leading to the formation of obnoxious blooms, floating scums or blankets of algae results into eutrophication. Most of the algal bloom does not seem to be utilized as food by the invertebrates or zooplankton, thereby, minimizing the predatory control. Biological decomposition of such algal masses in turn leads to oxygen depletion. In a poorly oxygenated condition, fish and other animal die and clean river is turned into a stinking drain.

iii. Spread of Infections/Diseases:

Micro-organisms, usually viruses, bacteria, some protozoans and helminthes occur in water bodies as a result of sewage disposal. Consumption of contaminated water causes water borne infectious diseases.

7. Essay on Industrial Water Pollution:

Pollution mainly caused by the discharge of industrial effluents into the water body is known as industrial pollution. These effluents contain a wide variety of inorganic and organic substances such as oils, greases, plastics, plasticizers, methylic wastes, suspended solids, phenols, pesticides, heavy metals and acids. Major industries of the country are located on or near the coastline or riversides.

The discharge of industrial wastes results into the following:

i. Organic substances deplete the oxygen content.

ii. Inorganic substances render the water unfit for drinking and other purposes.

iii. Acids and alkalies adversely affect the growth of fish and other aquatic organisms.

iv. Dye change the colour of water and affect the aquatic life.

v. Toxic substances cause serious damage to flora and fauna.

vi. Oil and other greasy substances interfere with the self-purification mechanism of water.

This occurs in large amounts in specific locations, making collection and treatment fairly simple to accomplish. There are water-using factories which are discharging wastes with a total BOD load about three to four times as large as the load from the sewered population. Only about 7 or 8% of industrial waste waters have been disposed of in municipal sewer system.

Wastes from textile manufacturing processes could be generated from the washing out of the impurities in the fibers, as well as in the discarding of chemicals used in the processing of the fibers. Generally, these wastes have been organic, have a high BOD, and are extremely alkaline.

Food-processing wastes from meat, dairy, and sugar beet processing, as well as brewing, distilling and canning operations, generate large amounts of organic by-products that have been disposed of in waste-water. When the waste-water is discarded, along with these by-products, it leads to high BODs and a consequent oxygen depletion in the receiving water via the same bacterial process involved in the decomposition of domestic wastes.

The effluent released from pulp and paper processing opera­tions has been a mixture of chemicals used in the digestion of raw wood chips, cellulose fibres, and dissolved lignin. This waste-water also has paper and wood preservatives, like penta- chlorophenol and sodium pentachlorophenate, as well as methyl mercaptan, all of which have been toxic to fish. This effluent has been brownish in colour and lowers the photosynthetic rate of aquatic communities by hindering sunlight penetration into the water column.

Consequently, the organic wastes from these plants increase the BOD of the receiving water, while colour imparted to the water interferes with sunlight penetration reduces photosynthesis, and further lowers oxygen levels.

Metal industries keep a wide array of contaminants in their waste-water. The specific contaminants and concentrations depend solely on the particular manufacturing process employed.

For example, steel mills employ and contaminate water in the coking of coal, the pickling of steel, and the washing of flue gases from blast furnaces. These waters, after use tends to be acidic and have various deleterious substances, like phenol, cyanogen, ore, coke, and fine suspended solids. Other indus­tries release traces of the metals produced or plated in their waste-water. Metals commonly found in these waste-waters have been chromium, mercury, nickel, lead, copper, and cadmium.

A variety of contaminants enter marine and fresh water environments in the effluents release from the various chemi­cal manufacturing plants. The release of acids results not only from acid manufacturing processes but from practically all other chemical manufacturing processes as well. In addition, synthetic fibres (e.g., rayons), bases, pesticides, and other organic and inorganic chemicals have been added, depending on the products being manufactured.

Most of the Indian rivers and fresh-water streams are seri­ously polluted by industrial wastes or effluents which come along waste-waters of different industries such as petro­chemical complexes; fertilizer factories; oil refineries; pulp, paper, textile, sugar and steel mills, tanneries’ distilleries, coal washeries, synthetic material plants for drugs, fibres, rubber, plastics, etc.

The industrial wastes of these industries and mills include metals (copper, zinc, lead, mercury, etc.), detergents, petroleum, acids, alkalies, phenols, carbamates, alcohols, cyanide, arsenic, chlorine and many other inorganic and organic toxicants. All of these chemicals of industrial wastes have been toxic to animals and may bring about death or sub lethal patho­logy of the liver, kidneys, reproductive systems, respiratory systems, or nervous systems in both in vertebrate and vertebrate aquatic animals.

Chlorine which is added to water to control growth of algae and bacteria in the cooling system of power station, may persist in streams to cause morta­lity of plankton and fish. Heavy fish motility in river Sone near Dehrion-on-sone in Bihar is reported to cause by free chlorine content of the chemical wastes discharged by factories near Mirzapur in U.P.

Mercury like other heavy metals such as lead and cadmium has cropped up as a toxic agent of serious nature. Mercury, a by-product of the production of vinyl-chloride, is used in many chemical industries and it is also a by-product of some incinerators, power plants, laboratories and even hospital. In Japan, illness and even death occurred in the 1950s among fishermen who ingested fish, crabs, and shell-fish contaminated with methyl mercury from Japanese coastal industries. This mercury poisoning produced a crippling and often fatal disease called Minamata disease.

Initial symp­toms of minamata disease included numbness of the limbs, lips, and tongue, impairment of motor control, deafness, and blurring of vision. Cellular degeneration occurred in the cerebellum, mid-brain, and cerebral cortex and this led to spasticity, figidity, stupor and coma. In Japan in 1953, due to Minamata disease 17 person died and 23 were become permanently disabled.

In India, all the 14 major rivers have become polluted. The river Damodar is perhaps the most heavily polluted river. River Mini-Mahi in Baroda has been other heavily polluted river which is having a variety of industrial and petrochemical wastes. The river Cooum flowing through Madras has been got polluted by sewage so much that not even the zooplanktons have been able to thrive in it. One litre of Cooum water is having as much as 900 mg or iron, 275 mg of lead, 1313 mg of nickel and 32 mg of zinc.

Besides heavy metals, very high level of phosphates, silicates and nitrates also occur in the water. Sul­phate levels ranging from 80-408 mg l–1 were the highest recor­ded among Indian rivers (The Times of India, May 27, 1987). The river Ganga from Hardwar to Calcutta is regarded as one unending sewer which is fit only to carry urban liquid waste, half burnt dead bodies, carrion, pesticides and insecticides.

Nearly 312 industrial units are dumping their waste into the river, only a dozen have effluent treatment facilities. The 27 cities contribute 902 million litres of waste-water to the river each day. The water of Ganga affect the health of 250 million people of northern India.

Many of our lakes, notably the Dal Lake, are becoming darkened, smelly and choked with excessive growth of algae.

8. Essay on Agricultural Water Pollution:

It includes sediments, fertilizers, and farm-animal wastes. These pollutants can all enter waterways as runoff from agri­cultural lands but farm animal wastes are an especially large problem near the large feedlots on which thousands of animals are concentrated.

Agricultural waste includes the pesticides that are sprayed on crops, as well as sediment, fertilizers, and plant and animal debris that are carried into waterways during periods of rainfall or as runoff and during the irrigation of farmland. Wastes generated by farm animals are also included in this category.

The practice of keeping large numbers of animals in a small area has led to an excess of animal wastes generated in and confined to a given area, where it has been economically impossible to distribute wastes for reuse as fertilizers. These materials become a problem when they are allowed to enter waterways during the cleaning of the confinement areas or during periods of heavy rainfall, when runoff carries them into adjacent waterways. Since these wastes are organic, they increase the BOD of the receiving waters.

Inorganic fertilizers, being plant nutrients, lead to over- fertilization of waterways when they enter these systems through runoff or during irrigation. The addition of excess plant nutrients can lead to a disturbance of the phosphorus/nitrogen balance in these systems as well as excessive plant growth. When the plants die, they settle to the bottom and, since they are organic, increase the BOD of the system during decomposition.

Soil erosion poses a fourfold problem. It increases the normal rate of filling of the waterways into which it washes, decreases the amount of fertile land for crop production, carries pesticide coated soil particles into the water, and decreases the transparency of the water, which limits photosynthesis. In addition, the sediment carried into fresh water systems tends to clog the gills of adult fish and settles out over incubating eggs, causing suffocation.

A remarkably large number of pesticides have come into widespread use in recent years. Many of these compounds have been not only non-biodegradable but are also only slightly soluble in water. Consequently, when sprayed on cropland they remain in the soil for long period of time.

During periods of heavy rainfall or when the crops are irrigated, they tend to be carried, as suspended particles, into surface, marine, or groundwater systems. In both fresh and marine systems they enter the food chain, undergo concentration in non-target organisms, and increase in animal tissue to alarming levels. In surface, fresh, and groundwater systems they may also enter the drinking-water supplies of various communities.

Water pollution can be caused by agricultural wastes such as fertilizers, pesticides, soil additives and animal wastes that are washed off from the land to the aquatic system through irrigation, rainfall and leaching. India uses about 16 kg/ha of fertilizers on an average. However, average all over the world is 54 kg/ha.

Netherlands alone uses 709 kg/ha. However, an increased use of pesticides has been observed in India from 2.8 Mt in 1975-76 to 6 Mt in 1994-95 and 9.7 Mt in 1994-95. The demand for fertilizers is non-biodegradable. In both fresh and marine systems they enter the food chain, accumulate in non-target organisms and increase in animal tissue to alarming concentrations. They may find entry into the drinking water supplies.

9. Essay on Solid Waste Pollution:

Solid waste varies in composition with the socioeconomic status of the generating community.

The following materials could be classified as solid waste:

(a) Garbage, which includes all decomposable wastes from households, as well as from food, canning, freezing, and meat-processing operations that are not disposed of in wastewater.

(b) Rubbish includes all non-decomposable wastes. These materials may be either combustible or noncombustible. Combustible materials would include garden wastes, cloth, and paper. Non-combustible materials include masonry, some chemicals, metals, and glass.

(c) Sewage sludge is generated from the settling processes in primary, secondary, and tertiary treatment methods as well as the solids from cesspools, which must be removed periodically.

(d) Miscellaneous materials include industrial wastes, like chemicals, paint, and explosives, as well as mining wastes, such as slag heaps and mine tailings.

The disposal of solid waste poses many problems, depending upon both the type of waste and the disposal method employed. The majority of the waste classified as combustible – rubbish, garbage, and sewage sludge has been disposed of by one of three major methods – incineration, using it as landfill, or disposal by ocean dumping. Incineration generally gives to air pollution; landfill operations or ocean dumping lead to water contamination.

If landfill disposal is used, the material, as it decomposes, will dissolve in or become suspended in the rain­water percolating into the ground and thus into subsurface aquifers. This tends to contaminate not only groundwater but also surface waters, since the two systems are ultimately inter­connected.

Because of the highly organic nature of this material, a large BOD is placed on the receiving waters, and the sediment becomes coated with a highly organic ooze. Non-combustible materials are generally disposed of in landfill sites or by ocean dumping.

Solid waste varies in composition with the socio-economic status of the generating community.

The following materials could be classified as solid waste:

i. Garbage – Decomposable wastes from households, food, canning, freezing and meat processing operations that are not disposed-off in wastewater.

ii. Rubbish – All non-decomposable wastes, garden wastes, cloth, paper, glass, metals and chemicals.

iii. Sewage Sludge.

iv. Miscellaneous Materials – chemicals, paints, explosives and mining wastes.

River or ocean dumping of these materials leads to water pollution. This tends to contaminate surface as well as ground water. Because of a high organic nature of this material, a large BOD is placed on the receiving waters and the sediment becomes coated with a highly organic ooze. Non-combustible materials are generally disposed-off by ocean dumping.

The National Environmental Engineering Research Institute (Nagpur, India) has categorized sea off Mumbai upto 5 km as one of the most polluted coastline where 1,800 million liters of city’s discharge is dumped every day. In 1994, 800 truckloads of garbage was washed onto the Juhu beach in a single night. Others adding to the coastal pollution include foreign liners docking along the Bombay Port Trust (BPT) which openly dump their wastes into the sea and leave a huge trail of fuel along the coastal stretches while departing.

10. Essay on Thermal Pollution: (401 Words)

Thermal pollution takes place because many electric generating companies use water in the process of cooling their generators. This heated water is then released into the system from which it was drawn, causing a warming trend of the surface waters. Thermal pollution results when the heated effluent is released into poorly flushed systems. In these cases permanent temperature increases often result, which tend to decrease the solubility of dissolved oxygen. In lakes it also becomes possible to bring about nutrient redistributions and prolong summer stagnation periods.

When heated water gets released into large, well-flushed marine systems there is little if any permanent temperature rise. There are, however, problems related to the operation of plants utilizing marine waters in the cooling process. Evidence reveals that sea water tends to corrode the cooling pipes, which are generally constructed of a copper nickel alloy termed Monel. These metals readily dissolve in the heated seawater and are then released into the marine environment together with the heated effluent. This adds to the nickel and copper concentra­tions of these systems.

In addition, the screens covering the water-intake pipes rapidly foul with marine organisms, which decreases the flow of water into the plant. The screens have been commonly cleaned by using a concentrated detergent solution or copper sulfate. These cleaning materials have been then released into and contaminated the surrounding waters.

An increase in the optimum water temperature by industrial processes (steel factories, electric power houses and atomic power plants) may be called as thermal pollution. Many industries generate their own power and use water to cool their generators.

This hot water is released into the system from where it was drawn, causing a warming trend of surface waters. If the system is poorly flushed, a permanent increase in the temperature may result. However, if the water is released into the well flushed systems, permanent increase in temperature does not occur.

Many organisms are killed instantly by the hot water resulting into a high mortality. It may bring other disturbance in the ecosystem. The eggs of fish may hatch early or fail to hatch at all. It may change the diurnal and seasonal behaviour and metabolic responses of organisms. It may lead to unplanned migration of aquatic animals. Macrophytic population may also be changed. As temperature is an important limiting factor, serious changes may be brought about even by a slight increase in temperature in a population.

11. Essay on Oil Pollution: (352 words)

There are about 15 million water crafts on navigable waters throughout the world. Their combined waste discharges are equivalent to a city with a population of 2,000,000. Thus oil pollution, an oxygen demanding waste, is of concern not only from sensational major spills from ships and offshore drilling rigs but also from small spills and cleaning operations.

The information available on oil pollution in Indian Ocean is fragmentary. In all, 6,689 observations were made on oil slicks and other floating pollutions along the tanker and trade routes across the northern Indian Ocean, of these, oil was sighted on 5582 occasions. The percentage of oil sightings ranged from 51 to 96. The number increased away from the source of oil, that is from the ballast and bilge washings and northern Indian Ocean is well known for oil slicks.

Observations on the floating petroleum residues from the Indian Ocean region show variations in time and are fairly high occasionally along the tanker routes. In the Arabian Sea, the concentration ranged from 0 to 6.0 mg/m2 with a mean of 0.59 mg/m2. The range in the Bay of Bengal tanker route varied from 0 to 69.75 mg/m2. These figures indicate that the tanker route in the Bay of Bengal is relatively more polluted than the Arabian Sea.

A layer of oil floating on the ocean surface can interfere with the exchange of oxygen and carbondioxide and reduce the rate of photosynthesis of marine plankton and the respiration of marine animals. Fuel oil added to sea water in very low concentration (199 ppb) depresses photosynthesis.

The death of birds from oil spills has attracted much attention. In the Torrey Canyon incident in 1967, an estimated 40,000 to 100,000 birds died. The Fort Mercer and Pendleton Collision in 1952 reduced the wintering population of eider ducks from 5,00,000 to 1,50,000.

Some believe that the jackars penguin, which lives in South Africa, is endangered because floating oil from tankers rounding the Cape of Good Hope is killing hundreds of thousands of these birds each year. The chronic effects of oil spills appear less serious than the acute effects.

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