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Environmental Pollution and Its Control

Preprint · September 2018

DOI: 10.13140/RG.2.2.26048.17927




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University of Calcutta


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Environmental Pollution and Its Control


Pollution is an unfavourable alteration in the physical, chemical or biological characteristics of air, water and land that may or will adversely affect human life, industrial life, industrial progress, living conditions and cultural assets.

Thus it is a sort of negative stress exerted on the positive health of the ecosystem.

The substances that cause the undesirable changes in the air, water and land are referred to as the pollutants. Thus, pollutant is a substance (e.g., dust, smoke), chemicals (e.g., SO2 or Methyl mercury) or factor (like heat, noise etc.) that on release into the environment has an actual or potential adverse effect on human interests. According to the Indian Protection Act (1986) “… a pollutant has been defined as any solid, liquid or gaseous substance present in such concentration as may be or tend to be injurious to the environment…” Various types of pollutants ranging from gaseous pollutants to radioactive wastes exist in nature. However for convenience, the entire pollutant spectrum may be dived into two broad categories namely biodegradable and non-biodegradable pollutants.

Substances like aluminium cans, heavy metals (like Zn, Cu, Mn, Fe, Co, ni, Pb, Hg,

etc.) long-chain phenolic chemicals and DDT either do not undergo microbial degradation or degrade at extremely slow rates. Such substances are grouped under the category of non-degradable pollutants. These groups of pollutants often accumulate within the living tissues (a phenomenon called bioaccumulation) and get “biologically magnified” while they move along the food chains towards the members of higher tropical level.

The biodegradable pollutants include domestic sewage which can be easily decomposed by microbial actions into smaller fragments or elements that can be again recycled.


According to WHO, air pollution is defined as “.... Phenomenon in which substances put into air by the activity of mankind into concentration sufficient to cause harmful effect to his health, vegetables, property or interfere with the enjoyment of his property ...”

Causes of Air Pollution

The various sources of air pollution are highlighted here:

1. Industrial pollutants: CO, CO2, SO2, H2S and hydrocarbons are most common


air pollutants which are discharged into air from industrial chimneys and power houses. These gases are produced due to burning of fossil fuels and by combustion of lignite at thermal power stations. Various fluorine compounds (HF, F2, SiF4, H2SiF6 etc.) are emitted from phosphate fertilizer manufacturing plants (since large amounts of fluorine are present in phosphate rock), aluminium extraction (where cryolite i.e., Na3AlF6 is used to lower the melting point of the mixture of CaF2, Al2O3 and Na3AlF6), ceramic firing, steel making and some chemical processing. Many metallurgical processes release dust and fumes which are loaded with Pb, Cr, Ni etc. Many chemical industries release hydrochloric acid, chlorine, oxides of nitrogen, Zn, Pb, As, oxides of Cu, in addition to SO2, CO and H2S. It has been observed that industrial processors like metallurgical plants and smelters, chemical plants, petroleum refineries, pulp and paper mills, sugar mills and cotton mills and synthetic rubber manufacturing plants are responsible for about one-fifth of the air pollution.

2. Automobiles: Automobiles (cars, scooters, motor cycle etc.) have been regarded as the greatest sources of air pollution. They produce nearly two-thirds of the carbon monoxide and one half of the hydrocarbons and nitrous oxides. The automobile exhaust has also leaded gas and particulate lead.

The combustion of petroleum emits particulate lead compounds. The particulate lead compounds emitted from petroleum combustion have profound adverse influence on biotic community.

Benzene, toluene and xylene are the three volatile organic compounds (VOC) present in urban atmosphere mainly due to use of petrol and diesel in automobiles.

Out of these three organic compounds, the concentrations of benzene in air showed strong correlations with the incidence of cancer. The limit value of benzene in air for health safety should not exceed 10 µg/m3.

3. Burning of Fuels: Fossil fuels are the sources of energy for cooking, heating, lightening our houses, washing clothes through washing machine, or for running TV etc. Coal and a variety of hydrocarbons including methane and soot, ashes and SO2 are also the products of coal burning. It has been recorded that electrical power plants, burning fossil fuels, particularly coal and sometimes petrol or diesel, produce two- thirds of the SO2.

In majority of the Indian cities, towns and villages cooking is done by burning colas, which is an important cause behind the increment of benzene concentration in the atmosphere. While in most of the developed countries, the most toxic benzene is much less than toluene and xylene in the urban air, in the third world countries, the picture is totally reverse. In Kolkata, more that 70% of the families still use coal chullas which account for high benzene load in the city air.

4. Aircraft Emissions: The pollution from the aircraft is also an important component of the total air pollution problem in the world. Aircrafts are responsible for about 2.5% of the CO emissions and about 1%

of the hydrocarbon emissions, but only negligible amounts of the other major air pollutants. The smoke emitted from jet aircraft is composed largely of fine particles approximately 0.5µm in diameter, which are completely burnt. As these particles scatter light quiet well, they often reduce visibility.

5. Agricultural Activities: Burning of forest areas, grasslands etc. for pastures and croplands produces about 60 to 65% of CO2. About 40% of methane is produced from paddy fields, guts of livestocks and also from burning of biomass.

Crop spraying and dusting for pest and weed control are responsible for emitting organic phosphates, chlorinated hydrocarbons, arsenic and lead into air.


6. Ionizing Radiation: These radiations are characterized by sufficiently great energy to ionize atoms and molecules. Ionizing radiation like alpha and beta particles are produced during nuclear explosions, scientific experiments where radio-isotopes are used and atomic weapon testing.

Radiations are also caused by naturally occurring radioactive substances.

7. Cosmic Radiation: Cosmic rays are high energy charged particles (mostly protons) of extra terrestrial origin, which are important source of natural radiations. The earth’s atmosphere is under the continuous bombardment of high energy particles coming from outer space. These particles are the primary cosmic rays. As they penetrate into the atmosphere, primary cosmic rays loss energy and gradually disappear on colliding against the oxygen and nitrogen atoms of the air. At the same time, however, they give rise to secondary rays mostly different in nature from the primary particles and, of course, of lower average energy. Thus, at each point with the atmosphere, one finds a radiation consisting partly of primary particles, and partly of secondary particles. This radiation may be denoted as local cosmic radiation.

8. Suspended Particulate Matter (SPM): SPM is a major air pollutant. Dust is generated from sources such as coal dust (from oil refineries, power plants etc.,) cement dust, silica dust (from stone crushing). A huge amount of dust is also blown by transport vehicles.

Incidences of high lead dust were recorded in some pockets of the city of Kolkata. In Picnic Garden area of Kolkata, there are a number of lead factories producing lead ingots and lead alloys. In the dining table of some local houses, the concentration of lead in the dust exceeded 5,000µg/gm (Chakraborti, 1996).

Effects of Air Pollution

Dust, smoke and other suspended particulate matter reduce the visibility. Some of the aerosols as H2SO4 mist, (NH4)2SO4 mist and water vapour influence the vertical temperature profile in the atmosphere. It affects the thermal mixing and also leads to green house effects and depletion of ozone layer. Air pollution also reduces the aesthetic value of places and exerts considerable adverse effects on the health of biota. The various effects of air pollution are discussed separately.

Effects of Air Pollution on Climate

In urban areas air pollution causes several effects like increase of air temperature, lowering of wind speed, attenuation of solar radiation etc. The particulate matter in the atmosphere, whose urban concentrations are typically 10 times those of rural areas, is capable of reducing the amount of solar radiation falling on the city by 15 to 20%.

Green house effect is also a direct consequence of air pollution. A large amount of CO2 gets introduced into the atmosphere due to burning of fossil fuels, furnaces etc. The gas gets confined exclusively to troposphere.

In dense concentration, it can act as a serious pollutant. The temperature at the surface of the earth is being maintained by the energy balance between the sun’s rays that strike the planet and the heat that gets radiated back into the space.

Some of the sun’s rays that penetrate the thick layer of CO2 are able to strike the earth and get converted into heat. The heated earth is able to re-radiate this absorbed energy as radiations of longer wavelengths. Much of this does not pass through CO2 layer to the outer space but gets absorbed by the CO2 layer creating an addition of extra heat. An increased heating of earth may result in melting of the polar ice caps and finally cause a rise in the sea level. This phenomenon is termed as green house effect. Many workers have predicted that there is a high probability


of increment of the global temperature by 1.5 to 4.5°C by the year 2050.

Sometimes, in the presence of sunlight, atomic oxygen from the photochemical reduction of NO2 also react with a number of hydrocarbons (such as methane, ethane, toluene etc., all of which originate from burning of fossil fuels or directly from plants) to form reactive intermediates called radicals. These radicals then take part in a series of reactions to form still more radicals that combine with oxygen, hydrocarbons and NO2. This results in the regeneration of NO2, disappearance of nitric oxide, accumulations of ozone and formation of a number of secondary pollutants like formaldehyde, aldehydes and peroxyacetyl nitrate or PAN (C2H3O5N). All these collectively form photochemical smog.

The increased use of CFCs by human beings in recent times has another cause in air pollution. These obnoxious compounds emitted mainly by aerosols escape to stratosphere and react with ozone. A sharp drop in the protective ozone layer (about 40%) over Antarctica could have been caused by human produced pollutants. This may ultimately pave the way of global temperature rise.

Effects of Air Pollution on Human Health Human health is seriously affected by air pollution and in extreme cases many diseases may be fatal. Diseases like asthma, bronchitis, pollen allergies, lung cancer are all associated with air pollution. Baker et al. (1968) reported that in many American cities along the Eastern Seaboard increasing frequencies of bronchitis, cough, soar throat, wheezes, eye irritations and general ill health in people occurred as air pollution level increased. Mountain et al.

(1968) reported the occurrence of respiratory problems in children less than 8 years in the city of New York.

Air pollution can also be the cause of cancer.

Higher benzene soluble organic matter (BSOM) in city air means that the air is more polluted and usually automobiles and coal burning are responsible for higher BSOM value. In BSOM, there lie a group of compounds known as Polynuclear Aromatic Hydrocarbon (PAH) and many of them are suspected carcinogens (like benzapyrene). Evidences from epidemiological studies suggest an increase of one benzapyrene unit corresponds to an increase of 5% in the lung cancer death rate.

The pathological effects of various air pollutants along with their sources are given in Table 7.1

Table 7.1: Pathological effects of some common air pollutants (After Southwick, 1976)

Pollutants Source Pathological effect

Aldehydes Thermal decomposition of fats, oil and

glycerol Irritate nasal and respiratory tracts

Ammonia Chemical processes, dye making, explo-

sives, fertilizer Inflames upper respiratory passages Arsine Processes involving metals or acids

containing arsenic soldering Breaks down red cells in blood, damages kidneys and causes jaundice

Carbon monoxide Gasoline motor exhausts, burning of coal Reduces oxygen carrying capacity of blood Chlorine Bleaching cotton and flour, many other

chemical processes Attacks entire respiratory tract and mucous membranes of eyes, cause pulmonary edema

Hydrogen cyanide Fumigation, blast furnaces, chemical

manufacturing, metal plating Interferes with nerve cells, produces dry throat, indistinct vision and headache



Effects of Air Pollution on Aesthetic Value 1. Coal dusts are a source of nuisance for

household articles and impart a dirty look.

2. The stone in Parthenon in Athens has deteriorated in the past 50 years for air pollution. Similarly statue of Liberty is corroded from SO2 and NO2 and Taj Mahal from SO2 emitted from Mathura refineries.

Soot and tar stick to the building stones and painted surface, which are very difficult to remove completely.

Prevention and Control of Air Pollution Air pollution is regarded as a grave danger for the healthy sustenance of all forms of life on this earth. The various measures to control air pollution are given below:

1. Pollution caused by two stroke engines can only be minimized by using the technology for four stroke engines. In case of three wheelers, the Government can insist to design their engine in such a way so that they can run on LPG.

2. Sulphur free and lead free fuel should be used for motor vehicles.

3. The height of the chimneys of factory should be tall enough to reduce the rate of pollution at the ground level.

4. To remove the particulate matter in the smoke, it should be filtered before releasing into the air.

5. Plantation should be done on a large scale.

Plants like Ficus variegata, Phaseolus vulgaris, Coleus bulmeri can fix CO easily.

Some other plants like Pinus sp., Juniperus sp., Quercus sp., Vitis sp. can use oxides of nitrogen. To reduce the effects of automobile pollution, the free space of the city area may be given a vegetation cover on the basis of the Air Pollution Tolerance Index (APTI) of trees. Some city plants has been identified to store carbon in considerable amount in their Above ground Biomass that can be planted in large scale to reduce the level of carbon dioxide in the atmosphere.

6. Control equipments like gravity settling tanks porous filters and electrostatic precipitators should be installed in factories to minimize air pollution. The method used for pollutant separation is dependent on the size of the pollutant particles. Gravity settling chambers are used for particles having size more than 50 µm. Electrostatic precipitators or Cyclone collectors are used for small sized particles.

Cyclones collectors contain a camber in which gas stream with particulate matter is whorled round through a tight circular spiral. Thus particulate pollutants are centrifuged, collected and removed. In electrostatic precipitators, precipitation is due to electric charging of particles and collecting surface bears an opposite charge to attract them.

Pollutants Source Pathological effect

Hydrogen fluoride Petroleum refining, glass etching, Al and

fertilizer production Irritates and corrodes all body passages Hydrogen sulphide Refineries and chemical industries,

bituminous fuels Causes nausea, irritates eyes and throats Nitrogen oxides Motor vehicles exhausts, soft coal Inhibits cilia action so that soot and dusts

penetrates far into the lungs Phosgene

(Carbonyl chloride) Chemical and dye manufacturing Induces coughing irritation and sometimes fatal pulmonary edema

Sulphur dioxide Coal and oil combustion Causes chest constriction headache, vomit- ing and respiratory ailments


particles Incinerators, any manufacturing units Causes emphysema, eye irritations and possibly cancer


Through this technique, particles with size of 5-20 µm can be removed to the extent of 95%.

7. Permanent air monitoring stations should be set up in the core area of the city to monitor the air quality throughout the year.


The term water pollution may be defined as the addition of substances or heat to such a level, which is harmful to humans, animals or any desirable aquatic life, or otherwise causes significant departures from the normal activities of various living communities in or near bodies of water. In practical, the term water pollution refers to several types of aquatic contamination like enrichment of nutrient in lakes and rivers from sewage and fertilizer, introduction of toxic chemicals in water bodies to such a level that the biota are affected to considerable extent etc.

Causes of Water Pollution

The various causes of water pollution may be described on the basis of origin of pollutants that deteriorate the water quality. The important sources of such pollutants are discussed here.

1. Domestic Wastes: These wastes arise from small sources, but ultimately spread over a

large area. These include waste water from homes and commercial establishments. The domestic wastes are usually contaminated with nitrates and phosphates and are often responsible for eutrophication - a phenomenon of rise of algal density due to enrichment of nutrient in the ambient water. When domestic wastes are dumped into water bodies, the aquatic community in the immediate vicinity do not show any significant alteration. This is because the organic wastes do not get time to decay just at the outfall site and therefore the dissolved oxygen level does not show any considerable variation. However, somewhat further away, conditions become worse as bacteria and fungi start degrading the organic sewage at the expense of dissolved oxygen.

2. Industrial Wastes: Industries are major sources of water pollution. A large number of factories and industries located on the banks of rivers and also in the coastal areas discharge their effluents without adequate treatment into the surrounding water bodies. Most of the Indian rivers are polluted by various types of industries (Table 7.2).

Sometimes the industrial wastes carry bulk of conservative wastes (non-degradable TABLE 7.2: Sources of pollution of some major Indian rivers

River Sources of Pollution

Kali at Meerut Sugar mills; distilleries; paint, soap, rayon, silk, tin and glycerine industries.

Jamuna near Delhi DDT factory, sewage, Indraprastha Power Station (Delhi).

Ganga at Kanpur Jute, chemical, metal and surgical industries; tanneries, textile mills and great bulk of domestic sewage having high organic matter.

Gomti near Lucknow (U.P.) Paper and pulp mills; sewage.

Dajora in Bareilley (U.P.) Synthetic rubber factories

Damodar between Bokaro and Panchet Fertilizers, fly ash from steel mills, suspended coal articles from washeries, and thermal power station.

Hooghly near Kolkata Power stations; paper pulp, jute, textiles, chemical mills, paints, varnishes, metal, steel, hydrogenated vegetable oils, rayons, and soap, match, shellac and polythene indus- tries and sewage.



pollutants), which accumulate inside the body tissue of flora and fauna inhabiting the aquatic system where the industrial wastes are discharged. Such process is highly dangerous as it can pose threat to human health through food chain. A recent study conducted by Banerjee et al. (2000) in the north eastern Bay of Bengal showed considerable accumulation of heavy metals in some edible fishes of coastal waters (Table 7.3).

3. Agricultural Wastes: The agricultural wastes include sediments, fertilizers, and farm animal wastes. These pollutants can enter the adjacent water bodies as runoff from agricultural lands. In recent years there has been an increased use of agricultural chemicals, notably pesticides and fertilizers.

The availability of low priced chemical fertilizers has led to rapid increase in their usage. Agricultural wastes can also lead

to eutrophication as plant nutrients and fertilizers contribute appreciable amount of nitrates and phosphates to the ambient media. The greatest agricultural pollution at present is probably due to soil erosion by water and wind, as many agricultural pollutants like pesticides and phosphates are transported by sediments to water bodies.

4. Shipping Wastes: These include both human sewage and other wastes, the most important of which is oil. About half of the crude oil produced per year is transported by sea. After unloading a cargo of oil from a tanker, it carries sea water as ballast. It is a general practice to fill several of the tanks (25% to 30% of the total capacity of the tanker) with sea water to ballast the ship for the voyage back to loading terminal. These ballast water are discharged prior to filling the tanks with new oil. When a tanker is unloaded it cannot be completely cleaned Table 7.3: Concentration of Pb in the muscle tissue of fish samples collected from Frasergaunge

Fin fish species Common local name Pb (in µg/gm dry wt.)

Tenualosa ilisha Ilish 14.84

Pampus argenteus Pomfret 3.82

Liza parsia Parse 10.65

Liza tade Bhangone 19.11

Polynemus paradiseus Tapse 7.62

Thunnus albacares Tuna 3.38

Coilia neglecta Ruli 2.65

Cynoglossus sp. Banspata 4.16

Scatophagus argus Paira chanda 6.43

Ilisha elongata Dhala 18.08

River Sources of Pollution

Sone at Dalmianagar (Bihar) Cement, pulp and paper mills.

Bhadra (Karnataka) Pulp, paper and steel industries.

Coom, Adyar and Buckinghum canal (Madras) Domestic sewage, automobile workshops.

Cauvery (Tamil Nadu) Sewage, tanneries, distilleries, paper and rayon mills.

Godavari Paper mills.

Siwan (Bihar) Paper, sulphur, cement, sugar mills.

Kulu (between Bombay and Kalyan) Chemical factories, rayon mills and tanneries.

Suwao (in Balrampur) Sugar industries.


because some oil remains on the bottom and some cling to the sides of the tank. The ballast water inevitably become contaminated with this remaining oil and is responsible for the deterioration of water quality.

5. Radioactive Wastes: The marine and estuarine systems receive radioactive wastes mainly from the nuclear power plants, nuclear power ships and sub-marines. Also extensive use of radio isotopes as tracers in the fields of medicine, biology, chemistry and biotechnology contribute radioactive substances in the city’s drainage system.

Other major sources of radioactive pollutants in the marine and estuarine compartments originate from weapon testing and leaching of radioactive material from soil or sediment which adds to the amount of radiation of the sea.

6. Aquaculture Wastes: Aquaculture encompasses the culture of aquatic organisms like finfish, shellfish, seaweeds, algae etc. in a controlled condition. Although fresh water aquaculture has not flourished yet to the expected target, but the coastal aquaculture, particularly the shrimp culture has achieved a unique position in the Indian sub-continent. A variety of finfishes, oysters, mussels, sea cucumbers, crabs and lobsters are in the export list of India, but shrimp is the single dominant item in the export basket of our marine food which accounts for almost two-thirds of the total export earnings. To increase the rate of shrimp production (which is usually expressed in tonnes per hectare) from the shrimp culture farms, the stocking density is also greatly increased along with simultaneous input of artificial feed and fertilizers. All these processes greatly increase the nutrient concentrations and organic load per unit area or percent weight of shrimp production which often exceeds the assimilatory capacity of system and results in aquatic pollution. The left over artificial feed supplied for the shrimp growth also generates H2S in the pond bed through

microbial action. The uses of antibiotics like oxytetracycline to fight back the prawn diseases also pollute the water bodies to a great extent.

7. Heat: A large volume of water find use for cooling purposes by various industries, mainly the steam electric power plants.

Cooling water is discharged at a raised temperature, and this has profound adverse effect on the growth and physiology of aquatic biota. This is mainly due to the fact that enzymes of organisms exhibit a particular temperature range for their optimum activity, and beyond this range there is a high probability of enzyme denaturation.

Effects of Water Pollution

Water pollution causes several water borne infectious diseases like Cholera, typhoid etc. Plant nutrients and aquaculture wastes contribute NO3, PO4 and NH3 in the aquatic phase, which trigger the growth of algae leading to eutrophication. Nitrates in drinking water can cause methemoglobinemia in babies (blue babies), as in an infant’s stomach, the nitrate is transformed into nitrite, which acts on the blood haemoglobin to form methemoglobin.

The heavy metals discharged from various industries also accumulate in the body tissues of the aquatic organisms and affect their normal physiological processes and growth. The growth of tiger prawns Penaeus monodon cultured with the waste wasters of the Kolkata city have been reduced to a significant level in comparison to their normal growth (Mitra et al., 1999). The diversity of fish juveniles is also reduced by the presence of various pollutants particularly lead, which originate from antifouling paints used for conditioning fishing vessels and trawlers in coastal areas (Mitra et al., 2000). The organic wastes not only reduce the dissolved oxygen concentration to the aquatic phase, but also promote the growth of anaerobic bacteria. This ultimately poses a negative stress on the fish population of the water bodies. Oil pollution in coastal zone or estuarine area, often affects light


penetration and oxygen level in the column water by creating a film on the surface water.

This affects the biotic community structure

in the oil spilled area. The important adverse effects caused by water pollutants are shown in (Table 7.4)

Table 7.4: Water Pollutants: sources, effects and residence times

Pollutants Major anthropogenic

sources Adverse effects Residence time

Oxygen demand- ing organic wastes (biodegradable)

Domestic sewage, industrial wastes, animal wastes

Depletion of dissolved oxygen, death of fish, damage to plant life, foul smell

Days to weeks.

Pathogens Domestic sewage, animal

wastes Outbreak of water borne diseases Days to months.

Acids Industrial wastes, acidic

deposition Death of aquatic organisms, solubility of harmful substances increases

Up to years

Salts Irrigation, Industrial

wastes Increase of salinity, death of aquat- ic organisms, becomes unfit for drinking purpose, domestic use, industrial use and agricultural use


Heavy metals, arse-

nic etc. Industrial wastes, leach- ing from soils by acidic substances

Toxic to humans, animals and

aquatic life Months to years

Plant nutrients (NO3,

PO4) Agricultural, domestic

and industrial wastes Eutrophication, fish death, disrup-

tion of community structure Decades

Heat Cooling water from power

plants and other indus- tries

Solubility of oxygen decreases,

harmful to aquatic life Days Radioactive sub-

stances Mining of radioactive sub- stances, nuclear power generation

Carcinogenic and mutagenic Days to years

Chlorine and its

compounds Paper and other indus-

tries, water disinfection Fatal to fish possibly carcinogenic Variable Oil and grease Lubricants and solvents

etc., petroleum wastes Potential damage to ecosystem, taste and odour problems for drinking water

Days to years

Pesticides and

herbicides Agriculture, pesticide and herbicide manufacturing units

Toxic to aquatic life, mammals and humans, some chemicals are carcinogenic and mutagenic

Days to years

Other synthetic organics (Phenols ethers, chloroform nitrosamines etc.)

Industrial effluents Toxic to aquatic life, mammals and humans, some chemicals are carcinogenic

Months to years

Source: Viessman et al., 1985


Prevention and Control of Water Pollution Biodegradable pollutants present in water are easy to remove with microbial technology, but conservative pollutants like heavy metals cannot be degraded or decomposed and hence require expensive technologies for their removal.

Water is often referred to as universal solvent. Hence it is practically impossible to get water in pure state in nature. Modern society utilizes water as principle and stable resource for domestic, industrial and agricultural purposes, power supply and aquaculture and even for recreation by enclosing it in artificial reservoirs.

Pollution of water will definitely minimize these uses of water and will pose a negative impact on mankind. The various methods for minimizing and controlling water pollution are discussed here.

I. The existing sewage treatment methods (like primary, secondary and tertiary treatment) are very effective in removing selective pollutants from contaminated water.

Primary treatment is a mechanical process which simply removes solids. The relatively larger solid particles are separated by means of metal screens; sands and small stones settle in grit chamber from which the water passes to the sedimentation tank, where the velocity of water is drastically reduced and the small particles settle as sludge. Scum is removed from the upper most layers.

Secondary treatment is essentially biological process which has the efficiency to remove most of the organic matter. In the activated sludge process of secondary treatment, the incoming sewage is mixed with decomposer bacteria and air or oxygen. Thus the complex organic matter through this treatment is broken down into simpler forms. One important drawback of this method is that if any toxic, industrial chemicals enter the sewage, then the decomposer bacteria may be killed and the entire operation may be inhibited.

Tertiary treatment is able to remove virtually all the remaining contaminants.

Water leaving conventional secondary treatment still has most of the original phosphates and nitrates, many persistent insecticides and herbicides, disease causing bacteria and viruses, and perhaps a number of industrial, organic compounds.

Waste water that is not subjected to tertiary treatment contains the nutrients on which algae thrive.

II. The various physicochemical techniques used for removal of chemical, biological radiobiological pollutants are adsorption, electro-dialysis, ion exchange and reverse- osmosis. Of the various techniques, the reverse-osmosis technique is based on the removal of salts and other substances from water by forcing the later through a semi-permeable membrane under a pressure that exceeds the osmotic pressure so that the flow is in the reverse direction to the normal osmosis flow. In practice, this involves a porous membrane whose chemical nature has been such that it has a preferential attraction for solvent while repulsion for the solute. Reverse-osmosis is commonly used to desalinate brackish water and also finds suitable, effective and economical method for the purification of water polluted by sewage effluents.

Electrodialysis is one of the membrane processes developed commercially for desalting saline water to get portable water. This technique can be applied for treatment of wash effluents, especially in electroplating industries (Mayr et al., 1992). The method is used to separate and recover the valuable metals in the form of ions in solution also enable low ion concentration to be brought up to higher level, which can be reused in the process (Thampy et al., 1997).

Mercury discharge from chlor-alkali plants can be removed and recovered by mercury selective ion exchange resin. Phenolics in waste water produced from industries


such as pulp and paper mills, petroleum refineries, tanning industries and resin manufacturing units are removed by the use of polymeric adsorbents.

The polluted water can also be treated biologically by reusing it for fish culture, oyster culture, algal culture and for plant growth. A recent work done by Niyogi et al., (1997) in the Haldia industrial zone of West Bengal, has revealed the excellent growth of some mangrove species in the estuarine water contaminated with heavy metals.

Inspite of considerable concentrations of zinc, copper and lead in the aquatic phase and vegetative parts (root, stem and leaves) of the mangrove species Sonneratia apetala, the growth rate has been accelerated, proving its excellent absorbing capacity of heavy metals. These plants (the woody part) can later be used as source of wood for fencing, boat manufacturing etc. The water hyacinth (menace in the fresh water aquatic ecosystem) is also very effective in absorbing heavy metals in fresh water systems.

In order to control the water pollution, strict implementation of the laws like water (Prevention and Control of Water Pollution) Act, 1974 and the Environmental (Protection) Act, 1986 are extremely important. As a part of protecting and improving the quality of the environment, the standards for emission or discharge of environmental pollutants from the industries, operations or processes has been specified. Any deviation from these specified values must be seriously treated to discourage pollution from point and non-point sources.

The legal actions to ban the semi-intensive shrimp culture farms in the coastal zone of India is a strict step in controlling the environmental pollution due to aquacultural industries. Considering the

various negative impacts like salinization of agricultural land (due to saline water intrusion), deterioration of land fertility, release of excessive nutrients and antibiotics in the coastal water etc., The Supreme Court of India ordered the coastal states on 11th December, 1996 that all aquacultural farms other than the traditional and improved traditional ones, operating within 500 metres of the high tide level (HTL) in the coastal zone be demolished by March, 1997.

The court also directed that no shrimp farm could be set up within 500 metres of HTL in the zone. In accordance with the principles of ‘sustainable development’ and

‘polluter pays’, the court also directed the government to set up a body under cause (3) of Section 3 of the Environment Protection Act, 1986. The said body will issue permits to the farmers of traditional aquaculture to adopt improved traditional farming system. Aqua-farming in mangrove areas, estuaries, wetlands salt pans and public land is also prohibited. Furthermore, the court ruled that the owners of the closed aquaculture units would be liable to pay six years wages as compensation to the workers as well as for eco-restoration of the affected areas by way of creating an Environmental Protection Fund.


The term ‘noise’ may be defined as ‘sound without value’ and is an unpleasant sound that is detrimental to health. Noise is capable of acting as a physiological stress in the human system and this can contribute to the onset of diseases depending on the neural-humoral stress response. Perhaps a better definition of noise is ‘wrong sound’ in the ‘wrong place’ and at the ‘wrong time’.

Noise pollution is basically unwanted and unpleasant sound, which gets dumped in the atmosphere causing an adverse effect to the surrounding with respect to the physical, chemical and biological characteristics.


Measurement of Noise

The acoustical measurement of noise involves the intensity, frequency and duration of the undesired sound. The physical measurement of sound involves its pressure related to the base or reference threshold. The difference indicates the intensity of a particular sound and is expressed as SPL. The ‘SPL’ is expressed in the following way.

SPL = 20 log10 P/P0

Where, SPL = pressure level of sound which is measured in units of decibels (db), P = average pressure of a measured sound and P0 = reference pressure which in physical measure is 0.0002 microbars.

This basic reference sound level (0.0002 microbars) again is considered to be the weakest audible pressure a young normal ear can detect under ideal listening conditions. In establishing decibel scale, the reference pressure P0 is assigned an intensity of 0 db, and more intense the sound is, the greater is the decibel level. Sound pressure and sound intensity at the limit of audibility naturally have been found to vary from person to person. For the sake of standardization they have been assigned the values of 2×10–5 N/m2 and 10–12 N/m2 respectively. Therefore when the sound pressure equals to 10–12 W/m2 and the intensity o sound equals to 10–12 W/m2, the intensity level of the sound equals to 0 decibels (Table 7.5).

Table 7.5: Sounds pressure, intensity and respective intensity level

Sounds pres-

sure N/m2 Intensity W/m2 Intensity level Decibels (dB)

2×10–5 10–12 0

2×10–4 10–10 20

2×10–3 10–8 40

2×10–2 10–6 60

2×10–1 10–4 80

2 (2×100) 10–2 100

2 (2×101) 1 (100) 120

2 (2×102) 100 (102) 140

Causes of Noise Pollution

With the advancement of technology, the pollution due to unwanted and unpleasant sound has become very common. The various sources of noise pollution are discussed here.

1. The noise pollution from aircraft is increasing steadily during recent years and especially close to international airport, already constitutes a very serious problem.

This problem has mainly arisen because of the widespread use of heavy long-range jet aircraft. Noise made by jet planes has been intrinsically more disturbing than that of propeller driven aircraft because it is of far higher pitch. Jet noise is caused by the violent mixing of the jet gases from the engine with the surrounding air. The intensity of the process becomes high during the take off stage when the engine delivers maximum thrust, and falls away rapidly as the aircraft climbs. During landing, the main source of high frequency noise has been the whine of the air compressor and turbine blades as the engine is throttled back. Aircraft pass close to the ground for quite a distance during the landing operation and this noise often constitutes a more sustained environmental nuisance than the intense noise of shorter duration produced during take off. Military aircraft often make annoyance in areas away from airfields because they are to be flown at low altitudes as part of normal training procedures.

2. Loud speakers used in various functions and occasions often cause noise pollution.

3. Sounds of crackers used in various festivals or for celebrating any success or victory are also the source of noise pollution. Diwali crackers often produce a noise of 120 db.

4. Electric horns used in vehicles often exceed the critical sound level and cause noise pollution.

5. Noise from construction sites has been generally far worse than noise originating from factories. This is mainly because the construction is carried out anywhere the


erection of roads, bridges and buildings become necessary. A list of various equipments that generate noise is given in (Table 7.6).

Table 7.6: Noise level generated from various equipment

Equipment Noise level at 15 metre

Tractor-scrapper 93 dB

Rock drill 87 dB

Unmuffled concrete

breaker 85 dB

Hand-held tree saw 82 dB

Large rotary diesel

compressor 80 db

One and half tonne

dumper truck 75 dB

Diesel concrete mixer 75 dB

6. Piling is another very noisy civil engineering operation that produces loud noise when the pile driver makes its impact.

7. In the industrial sector noises originate from processes causing impact, vibration or reciprocation movements, friction and turbulence in air or gas streams.

Effects of Noise Pollution

The generation of unnecessary noise in the environment is a type of pollution because it lowers the quality of life. The various adverse effects of noise on human beings are discussed here.

1. Noise pollution leads to development of cardiovascular problems like heart diseases and high blood pressure. Workers exposed to high noise level are having more circulatory problems, cardiac disturbances, neurosensory and motor impairment. The digital plethymography studies or the finger pulse amplitude tests indicate the extent or arteriolar constriction upon exposure to noise.

2. Noise may be decisive contributory factor in such diseases as peptic ulcer, hypertension, colitis, migraine headaches and nervous disorder.

3. Hearing loss is considered the major evil of a noisy environment. This can be classified into

i. Acoustic trauma denoting injury to ear due to the exposure of a very high intensity impact noise.

ii. Noise induced hearing loss (NIHL).

The hearing loss may occur due to an acoustic trauma following the impact of one or a few sudden exposures, or in other words, an intense release of acoustic energy as in the case of blasts and explosions. In such situations one or both the ears may be affected and it may involve the conductive as well as the sensorineural part of the ear.

4. Noise pollution is also affects the process of sleeping of an individual. Normally an individual requires about five hours of sleep which has an appreciable recuperative value.

Sleep helps recuperation of the cells worn out during the diurnal activities. The depth, duration and continuity are important for this congenial process. Noise, my however, interfere with all these three. Experiments undertaken at Canada have detected that a person’s sleep is altered when he exposed to a vehicle noise of 55dBA. When this increases to 60dBA, the intensity affects the deepest stage of sleep.

5. External loud sound often interferes with conversation and use of the telephones as well as enjoyment of radio TV programmes.

In places like office, school, colleges, universities and educational campuses.

Loud sound from external sources can create considerable disturbances as communications is of vital importance in these sectors.

Prevention and Control of Noise Pollution The various ways of controlling noise pollution are listed here.

1. Noise can be reduced at source by designing and fabricating of silencing devices for their use in aircraft engines, trucks, cars.

Motorcycles, industrial machines and home appliances.


2. The intensity of sound can be reduced by making a change in design and operation of machines, vibration control, introducing sound proof cabins and sound absorbing materials.

3. The noise pollution can be reduced by prescribing noise limits for vehicular traffic, ban on electric horns in certain areas and planning main traffic arteries, residential colonies, industrial establishments, amusement areas, creating of silent zones near hospitals and schools and redesigning of building to make them noise proof.

4. The penetration of noise from outdoor environment can be reduced by the following methods.

• Trees and shrubs may be planted in front of building to provide some absorption of sound.

• Construction of non-critical areas such as corridors, kitchens, bathrooms, elevators and service spaces in the noisy side and critical areas like bedrooms and living spaces on the quite side.

• Bathrooms walls, floor and ceiling should be sound insulated using construction of high sound insulation glasses.

5. Vegetation buffer zones must be created in several parts of the city. Efforts should be

taken to create roadside plantation using specific noise absorbing plants like ashok, neem, coconut etc.

6. Strict implementation of laws and disciplinary actions should be taken on the following aspects.

• The truck movement in the old cities should be prohibited from 6 a.m. to 12 midnight.

• A new plan of city should be done with the provision of truck terminal outside the city.

• Major transportation corridors should not be taken though the sectors.

• Entry of noise making vehicles in the sectors should be strictly restricted.

• The noise standard as prescribed by the Federal Highway Administration (FHWA) in 1973 for several categories of land use (Table 7.7) should be strictly followed.


Thermal pollution is defined as sudden increase or decrease in temperature of a natural body of water which may be ocean, lake, river or pond by human influence. This normally occurs when a plant or facility takes in water from a natural resource and puts it back with an altered temperature. Usually, these facilities use it as a Table 7.7: FHWA Noise Standard

Land Use Category Design noise level Description of land Category

A 60 dBA (exterior) Tracts of land in which serenity and quietness are of extraordinary significance and serve an important public need, and where the preservation of those qualities is essential if the area is to continue to serve its intended purpose. Such areas could include amphitheatres, particular parks or portions of parks, or open spaces which are dedicated or recognised by appropriate local official for activities requiring special qualities of serenity.

B 70 dBA (exterior) Residences, hotels, motels, public meeting rooms, school, churches, libraries, hospital, picnic areas etc.

C 75 dBA (exterior) Developed lands, properties or activities not included in category A and B

D For requirements on undeveloped lands

E 55 dBA (interior) Residences, hotels, motels, libraries, churches, hospitals and auditoriums.


cooling method for their machinery or to help better produce their products.

Causes of Thermal Pollution

1. Water as cooling agent in power, manu- facturing and industrial plants: Production and Manufacturing plants are biggest source of thermal pollution. These plants draw water from nearby source to keep machines cool and then release back to the source with higher temperature. When heated water returns to the river or ocean, the water temperature rises sharply. When oxygen levels are altered in the water, this can also degrade the quality and longevity of life in wildlife that lives underwater. This process can also wipe away streamside vegetation, which constantly depends on constant levels of oxygen and temperature. By altering these natural environments, industries are essentially helping decrease the quality of life for these marines based life forms and can ultimately destroy habitats if they are not controlled and careful about their practices.

2. Soil erosion: Soil erosion is another major factor that causes thermal pollution.

Consistent soil erosion causes water bodies to rise, making them more exposed to sunlight. The high temperature could prove fatal for aquatic biomes as it may give rise to anaerobic conditions.

3. Deforestation: Trees and plants prevent sunlight from falling directly on lakes, ponds or rivers. When deforestation takes place, these water bodies are directly exposed to sunlight, thus absorbing more heat and raising its temperature. Deforestation is also a main cause of the higher concentrations of greenhouse gases i.e. global warming in the atmosphere.

4. Runoff from paved surfaces: Urban runoff discharged to surface waters from paved surfaces like roads and parking lots can make water warmer. During summer seasons, the pavement gets quite hot, which creates warm runoff that gets into the sewer systems and water bodies.

5. Natural causes: Natural causes like volcanoes and geothermal activity under the oceans and seas can trigger warm lava to raise the temperature of water bodies.

Lightening can also introduce massive amount of heat into the oceans. This means that the overall temperature of the water source will rise, having significant impacts on the environment.

Effects of Thermal Pollution

Among recognized scientists and scholars, there are generally two schools of thought when it comes to the effects of thermal pollution. Some lean on the side of the negatives of this pollution on marine ecosystems and how it is detrimental to positive environmental practices. However, some lean towards the side that without these industries operating the way they do, then some of the most basic parts of human life would be completely obsolete. Waste water would not be able to be properly maintained, we would have no industries that could produce the goods we need, and so on. The effects of thermal pollution on ecosystems, however, greatly outweigh the benefits that industries have by participating in the act.

1. Decrease in DO (Dissolved Oxygen) levels:

The warm temperature reduces the levels of DO (Dissolved Oxygen) in water. The warm water holds relatively less oxygen than cold water. The decrease in DO can create suffocation for plants and animals such as fish, amphibians and copepods, which may give rise to anaerobic conditions. Warmer water allows algae to flourish on surface of water and over the long term growing algae can decrease oxygen levels in the water.

2. Increase in toxins: With the constant flow of high temperature discharge from industries, there is a huge increase in toxins that are being regurgitated into the natural body of water. These toxins may contain chemicals or radiation that may have harsh impact on the local ecology and make them susceptible to various diseases.


3. Loss of biodiversity: A dent in the biological activity in the water may cause significant loss of biodiversity. Changes in the environment may cause certain species of organisms to shift their base to some other place while their could be significant number of species that may shift in because of warmer waters.

Organisms that can adapt easily may have an advantage over organisms that are not used to the warmer temperatures.

4. Ecological impact: A sudden thermal shock can result in mass killings of fish, insects, plants or amphibians. Hotter water may prove favorable for some species while it could be lethal for other species. Small water temperature increases the level of activity while higher temperature decreases the level of activity. Many aquatic species are sensitive to small temperature changes such as one degree Celsius that can cause significant changes in organism metabolism and other adverse cellular biology effects.

5. Affects reproductive systems: A significant halt in the reproduction of marine wildlife (although this may be true, reproduction can still occur between fish – but the likelihood of defects in newborns is significantly higher) can happen due to increasing temperatures as reproduction can happen with in certain range of temperature. Excessive temperature can cause the release of immature eggs or can prevent normal development of certain eggs.

6. Increases metabolic rate: Thermal pollution increases the metabolic rate of organisms as increasing enzyme activity occurs that causes organisms to consume more food than what is normally required, if their environment were not changed. It disrupts the stability of food chain and alter the balance of species composition.

7. Migration: The warm water can also cause particular species of organisms to migrate to suitable environment that would cater to its requirements for survival. This can result in loss for those species that depend on them

for their daily food as their food chain is interrupted.

Control of Thermal Pollution

The following methods can be adapted to control high temperature caused by thermal discharges:

1. Cooling towers: Use of water from water systems for cooling systems for cooling purposes, with subsequent return to the water way after passage through a condenser, is called cooling process. Cooling towers transfer heat from hot water to the atmosphere by evaporation. Cooling towers are of two types:

i. Wet cooling tower: Hot water coming out from the condenser (reactor) is allowed to spray over baffles. Cool air, with a very high velocity, is passed from sides, which takes away the heat (from the hot water) and cools the water.

ii. Dry cooling tower: In this case hot water is allowed to flow in long spiral pipes. Cool air with the help of a fan is passed over these hot pipes, which cools down hot water. This cool water can be recycled.

2. Cooling ponds: Cooling ponds are the best way to cool thermal discharges. Heated effluents on the surface of the water in cooling ponds maximize dissipation of heat to the atmosphere and minimize the water area and volume.

3. Spray ponds: The water coming out from condensers is allowed to pass into the ponds through sprayers. Here water is sprayed through nozzles as fine droplets. Heat from the fine droplets gets dissipated to the atmosphere.

4. Artificial lakes: Artificial lakes are man made water bodies that offer once-through cooling. The heated effluents can be discharged into the lake at one end and water for cooling purposes may be withdrawn from the other end. The heat is eventually dissipated through evaporation.



Marine pollution has been defined as “the introduction by human, directly or indirectly of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities including fishing, impairment of quality for use of sea water and reduction of amenities”. Thus marine pollution is the harmful entry of chemicals, energy or particles into the ocean compartment. A big problem is that many toxins adhere to tiny particles, which are taken up by plankton and benthic organisms, most of which are filter feeders in nature. This results in bioaccumulation and biomagnification, while going up the ocean food chain.

The problems of global marine pollution are examined in terms of both short-term, acute, local effects and long-term, chronic, cumulative, world-wide effects of pollutants in the world’s oceans. The present pollution problems are most serious in coastal waters, which constitute only 10 per cent of the area of the oceans yet, together with the upwelling areas of the world, produce 99 per cent of the world fish catch. However, the long-term consequences of persistent, cumulative substances pose the greatest concern. The critical marine pollutants can be conveniently classified into five categories: (1) metals; (2) synthetic chemicals;

(3) petroleum hydrocarbons; (4) radionuclides;

and (5) solid wastes. Pollutants may enter the sea through rivers, atmospheric transport, ocean outfalls, ocean dumping, ships and such marine activities as mining. Atmospheric transport of pollutants and entry into the sea through fallout, rainout and washout have been considered an important rapid route for certain pollutants fromman’s activities on land to the world oceans. This particularly applies to the radionuclides and the polyhalogenated hydrocarbons, e.g. DDT and PCB’s, but may also be important to world-wide dispersion of metals and petroleum hydrocarbons.

Problems of marine pollution from ships, especially by oil, and from ocean dumping, are rapidly coming under control through national legislation and international conventions, such as the International Convention for the Prevention of Pollution from Ships, 1973, and the International Convention for the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, 1972. Control of atmospheric testing of nuclear weapons among the major nuclear powers, under the Treaty Banning Nuclear Weapons Tests in the Atmosphere, in Outer Space and Underwater, 1963, has largely stopped entry of radionuclides into the sea from fallout. There are stringent controls on nuclear power reactors, and other peaceful uses of atomic energy, so that in the absence of accidents, there is minimal entry of radionuclides into the sea from these sources.

Many scientific conferences on the marine environment are identifying the major pollution problems, examining the critical issues and determining ways in which a meaningful base- line survey can be conducted and a useful monitoring programme established. All the United Nations Specialized Agencies concerned with the marine environment continue to review certain pollution problems within their areas of responsibility. The MCO /FAO/Unesco/

WMO/WHO/IAEA/United Nations/UNEP(1) Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) examines some of the problems on an interdisciplinary basis in annual meetings, and in intersessional working groups. It advises member agencies and/or member governments, through the agencies, on marine pollution matters. The IOC/WMO IGOSS Pilot Project on Marine Pollution (Petroleum) Monitoring commenced in January 1975, with are view of the first year’s results in May and June 1976, and another review is planned for an indefinite date after 1977. (ICG) for the Global Investigation of Pollution in the Marine Environment (GIPME) met for its third and last session at Unesco, Paris, in July 1975 and prepared a comprehensive plan for the


global investigation of pollution in the marine environment and baseline study guidelines. The working committee for GIPME, which replaced ICG, met for its first session in Hamburg, from 18 to 22 October 1976. Progress is being made on scientific data exchange in marine pollution. Training courses and workshops are providing a means of educating technical people in developing countries on techniques of measuring and assessing marine pollution and in initiating regional projects investigating problems of marine pollution.

Different substances find their entry in the marine and estuarine environment in three basic forms namely solid, liquid and gas. The major categories of waste that enter into the ocean are listed in Table 7.8.

The pollutants discharged from these sources pose considerable effects on the community, species, cellular and even genetic levels. The magnitude of hazard ranges from moderate to extreme depending on the nature of the chemicals. A list of major marine pollutants and their effects are presented in Table 7.9.

Table 7.8: Potential sources of marine and estuarine pollution

S.No. Major sources of pollution

1 Domestic sewage

2 Sewage sludge

3 Industrial wastes

4 Solid wastes

5 Shipboard wastes

6 Aquacultural farms

7 Pesticides and Fertilizers

8 Offshore oil exploration and production wastes

9 Oil spills

10 Radioactive wastes

11 Heat: Thermal pollution from power plants

12 Fly ash from thermal power plants

13 Continental run-off

14 Antifouling paints

15 Barges and other metallic structures

16 Ocean mining

17 Precipitation of air borne pollutants

18 Oil from tanker cleaning and deballasting

19 Weathering of the earth’s crust

20 Volcanic eruptions

21 Natural submarine oil seeps

22 Dredge spoils

23 Military wastes (Weapon testing etc.)

24 Tourism and recreational activities


Table 7.9: Ranking of the major marine pollutants (Johnston, 1976)

Harm to living

resources Hazard to human

health Hindrance to maritime activi-


Reduction of amenity

Domestic sewage Important Important Slight Important

Pesticides Important Significant Negligible Negligible

Inorganic trade wastes Mainly slight Slight except Hg Negligible Negligible to slight Radioactive wastes Negligible Significant Negligible Negligible

Petroleum Significant Uncertain Significant Important

Organic chemicals Highly variable Some significant Negligible to slight Variable Organic trade wastes Some Important/

Significant Negligible Negligible to slight Significant to Im- portant

Military wastes Uncertain Uncertain Negligible Negligible

Waste heat Significant Negligible Negligible Negligible

Detergents Uncertain Negligible Important Important

Solid objects Slight Negligible Uncertain Significant

Inert solids and

dredged spoil Significant Negligible Uncertain Significant

Notes: “Important”—requires restrictive or preventive measures.

Slight”—caution required further study needed.

Negligible”—no restrictive action needed.

Uncertain”—special situations apart, no restrictive action needed.

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