POLLUTION AND POLLUTANTS
· Pollution may be defined as addition of undesirable material into the environment as a result of human activities.
· The agents which cause environmental pollution are called pollutants.
· A pollutants may be defined as a physical, chemical or biological substance unintentionally released into the environment which is directly or indirectly harmful to humans and other living organisms.
TYPES OF POLLUTION
Pollution may be of the following types:
· Air pollution
· Noise pollution
· Water pollution
· Soil pollution
· Thermal pollution
· Radiation pollution
· Air pollution is a result of industrial and certain domestic activity.
· An ever increasing use of fossil fuels in power plants, industries, transportation, mining, construction of buildings, stone quarries had led to air pollution.
· Air pollution may be defined as the presence of any solid, liquid or gaseous substance including noise and radioactive radiation in the atmosphere in such concentration that may be directly and indirectly injurious to humans or other living organisms, plants, property or interferes with the normal environmental processes.
· Air pollutants are of two types :
(1) suspended particulate matter, and
(2) gaseous pollutants like carbon dioxide (CO2), NOx etc.
Particulate pollutants :
· Particulate matter suspended in air are dust and soot released from the industrial chimneys.
· Their size ranges from 0.001 to 500 μm in diameter.
· Particles less than 10μm float and move freely with the air current.
· Particles which are more than 10μm in diameter settle down.
· Particles less than 0.02 μm form persisent aerosols.
· Major source of SPM (suspended particulate matter) are vehicles, power plants, construction activities, oil refinery, railway yard, market place, industries, etc.
Fly ash : (2015 prelims)
· Fly ash is ejected mostly by thermal power plants as by products of coal burning operations.
· Fly ash pollutes air and water and may cause heavy metal pollution in water bodies.
· Fly ash affects vegetation as a result of its direct deposition on leaf surfaces or indirectly through its deposition on soil.
· Fly ash is now being used for making bricks and as a land fill material.
Lead and other metals particles :
· Tetraethyl lead (TEL) is used as an anti-knock agent in petrol for smooth and easy running of vehicles.
· The lead particles coming out from the exhaust pipes of vehicles is mixed with air.
· If inhaled it produces injurious effects on kidney and liver and interferes with development of red blood cells.
· Lead mixed with water and food can create cumulative poisoning.
· It has long term effects on children as it lowers intelligence.
· Oxides of iron, aluminum, manganese, magnesium, zinc and other metals have adverse effect due to deposition of dust on plants during mining operations and metallurgical processes.
· They create physiological, biochemical and developmental disorders in plants
and also contribute towards reproductive failure in plants.
Gaseous pollutants :
Power plants, industries, different types of vehicles – both private and commercial use
petrol, diesel as fuel and release gaseous pollutants such as carbon dioxide, oxides of
nitrogen and sulphur dioxide along with particulate matter in the form of smoke.
All of these have harmful effects on plants and humans.
Table lists some of these pollutants, their sources and harmful effects.
Gaseous air pollutants: their sources and effects :
(CO and CO2)
burning of wood and coal
· Respiratory problems
· Green house effect
Sulphur compounds (SO2 and H2S)
Power plants and refineries
· Respiratory problems in humans
· Loss of chlorophyll in plants (chlorosis)
· Acid rain
Nitrogen Compound (NO and N2O)
Motor vehicle exhaust
· Irritation in eyes and lungs
· Low productivity in plants
· Acid rain damages material (metals and stone)
Hydrocarbons (benzene, ethylene)
Automobiles and petroleum industries
· Respiratory problem
· Cancer causing properties
Particulate Matter) (Any soild and liquid)
particles suspended in the air, (flush, dust, lead)
Thermal power plants,
metalurgical processes and automobiles
· Poor visibility, breathing problems
· Lead interfers with the development of red blood diseases and cancer.
· Smoge (skoke & fog) formation leads to poor visibility and aggravates asthma in patients
Fibres (Cotton, wool)
Textiles and carpet weaving industries
· Lung disorders
Prevention and control of air pollution
(i) Indoor air pollution :
· Poor ventilation due to faulty design of buildings leads to pollution of the confined space.
· Paints, carpets, furniture, etc. in rooms may give out volatile organic compounds (VOCs).
· Use of disinfectants, fumigants, etc. may release hazardous gases.
· In hospitals, pathogens present in waste remain in the air in the form of spores.
· This can result in hospital acquired infections and is an occupational health hazard.
· In congested areas, slums and rural areas burning of firewood and biomass results in lot of smoke.
· Children and ladies exposed to smoke may suffer from acute respiratory problems which include running nose, cough, sore throat, lung infection, asthama, difficulty in breathing, noisy respiration and wheezing.
(ii) Prevention and control of indoor air pollution :
· Use of wood and dung cakes should be replaced by cleaner fuels such as biogas, limited kerosene or limited electricity.
· The house designs should incorporate a well ventilated kitchen.
· Use of biogas and CNG (Compressed Natural Gas) need to be encouraged.
· Those species of trees such as baval (Acacia nilotica) which are least smoky should be planted and used.
· Charcoal is a comparatively cleaner fuel.
(iii) Prevention and control of industrial pollution
Industrial pollution can be greatly reduced by:
· use of cleaner fuels such as liquefied natural gas (LNG) in power plants, fertilizer
plants etc. which is cheaper in addition to being environmentally friendly.
· installing devices which reduce release of pollutants.
· Devices like filters, electrostatic precipitators, inertial collectors, scrubbers, gravel bed filters or dry scrubbers are described below:
(i) Filters :
· Filters remove particulate matter from the gas stream.
· The medium of a filter may be made of fibrous materials like cloth, granular material like sand, a rigid material like screen, or any mat like felt pad.
· Baghouse filtration system is the most common one and is made of cotton or synthetic fibres ( for low temperatures) or glass cloth fabrics (for higher temperature up to 290oC).
(ii) Electrostatic precipitators (ESP) :
· The emanating dust is charged with ions and the ionized particulate matter is collected on an oppositely charged surface.
· The particles are removed from the collection surface by occasional shaking or by rapping the surface.
· ESPs are used in boilers, furnaces, and many other units of thermal power plants, cement factories, steel plants, etc.
(iii) Inertial collectors :
· It works on the principle that inertia of SPM in a gas is higher than its solvent and as inertia is a function of the mass of the particulate matter this device collects heavier particles more efficiently.
· ‘Cyclone’ is a common inertial collector used in gas cleaning plants.
(iv) Scrubbers :
· Scrubbers are wet collectors.
· They remove aerosols from a stream of gas either by collecting wet particles on a surface followed by their removal, or else the particles are wetted by a scrubbing liquid.
(iv) Control of vehicular pollution :
· In cities like Delhi, motor vehicles need to obtain Pollution Under Control (PUC) certificate at regular intervals.
· This ensures that levels of pollutants emitted from vehicle exhaust are not beyond the prescribed legal limits.
· The price of diesel is much cheaper than petrol which promotes use of diesel.
· To reduce emission of sulphurdioxide, sulphur content in diesel has been reduced to 0.05%.
· Earlier lead in the form of tetraethyl lead was added in the petrol to raise octane level for smooth running of engines.
· Addition of lead in petrol has been banned to prevent emission of lead particles with the vehicular emission.
OZONE HOLE-CAUSES AND HARM DUE TO OZONE DEPLETION :
· The stratosphere has an ozone layer which protects the earth’s surface from excessive ultraviolet (UV) radiation from the Sun.
· Chlorine from chemicals such as chlorofluorocarbons (CFCs) used for refrigeration, air conditioning, fire extinguishers, cleaning solvents, aerosols (spray cans of perfumes, medicine, insecticide) cause damage to ozone layer chlorine contained in the CFCs on reaching the ozone (O3) layer split the ozone molecules to form oxygen (O2).
· Amount of ozone, thus gets reduced and cannot prevent the entry of UV radiation.
· There has been a reduction of ozone umbrella or shield over the Arctic and Antarctic regions. This is known as ozone hole.
· This permits passage of UV radiation on earth’s atmosphere which causes sunburn, cataract in eyes leading to blindness, skin cancer, reduced productivity of forests, etc.
· Under the “Montreal Protocol” amended in 1990 it was decided to completely phase out CFCs to prevent damage of ozone layer.
GLOBAL WARMING AND GREENHOUSE EFFECT :
· Atmospheric gases like carbondioxide, methane, nitrous oxide, water vapour, and chlorofluorocarbons are capable of trapping the out-going infrared radiation from the earth.
· Infra-red radiations trapped by the earth’s surface cannot pass through these gases and to increase thermal energy or heat in the atmosphere.
· Thus, the temperature of the global atmosphere is increased.
· As this phenomenon of increase in temperature is observed in green houses, in the botanical gardens these gases are known as green house gases and the heating effect is known as green house effect.
· If greenhouse gases are not checked, by the turn of the century the temperature may rise by 50C.
· This will melt the polar ice caps and increase the sea level leading to coastal flooding, loss of coastal areas and ecosystems like swamps and marshes, etc.
NOISE POLLUTION :
· Noise is one of the most pervasive pollutant. A musical clock may be nice to listen during the day, but may be an irritant during sleep at night.
· Noise by definition is “sound without value” or “any noise that is unwanted by the recipient”.
· Noise in industries such as stone cutting and crushing, steel forgings , loudspeakers, shouting by hawkers selling their wares, movement of heavy transport vehicles, railways and airports leads to irritation and an increased blood pressure, loss of temper, decrease in work efficiency, loss of hearing which may be first temporary but can become permanent in the noise stress continues.
· Noise level is measured in terms of decibels (dB). W.H.O. (World Health Organization) has prescribed optimum noise level as 45 dB by day and 35 dB by night. Anything above 80 dB is hazardous.
Effects of noise pollution :
· Noise pollution is highly annoying and irritating.
· Noise disturbs sleep, causes hypertension (high blood pressure), emotional problems such as aggression, mental depression and annoyance.
· Noise pollution adversely affects efficiency and performance of individuals.
WATER POLLUTION :
· Addition or presence of undesirable substances in water is called water pollution.
· Water pollution is one of the most serious environmental problems.
· Water pollution is caused by a variety of human activities such as industrial, agricultural and domestic.
· Agricultural run off laden with excess fertilizers and pesticides, industrial effluents with toxic substances and sewage water with human and animal wastes pollute our water thoroughly.
· Natural sources of pollution of water are soil erosion, leaching of minerals from rocks and decaying of organic matter.
· Rivers, lakes, seas, oceans, estuaries and ground water sources may be polluted by point or non-point sources.
· When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into a water body it represents point source pollution.
· In contrast non-point sources include discharge of pollutants from diffused sources or from a larger area such as run off from agricultural fields, grazing lands, construction sites, abandoned mines and pits, roads and streets.
Pollution due to pesticides and inorganic chemicals :
· Pesticides like DDT and others used in agriculture may contaminate water bodies.
· Aquatic organisms take up pesticides from water get into the food chain (aquatic in this case) and move up the food chain.
· At higher trophic level they get concentrated and may reach the upper end of the food chain.
· Metals like lead, zinc, arsenic, copper, mercury and cadmium in industrial waste waters adversely affect humans and other animals.
· Arsenic pollution of ground water has been reported from West Bengal, Orissa, Bihar, Western U.P.
· Consumption of such arsenic polluted water leads to accumulation of arsenic in the body parts like blood, nails and hairs causing skin lesions, rough skin, dry and thickening of skin and ultimately skin cancer.
· Pollution of water bodies by mercury causes Minamata disease in humans and dropsy in fishes.
· Lead causes displexia, cadmium poisoning causes Itai – Itai disease etc.
· Oil pollution of sea occurs from leakage from ships, oil tankers, rigs and pipelines.
· Accidents of oil tankers spill large quantity of oil in seas which kills marine birds and adversely affects other marine life and beaches.
(ii) Thermal pollution :
· Power plants- thermal and nuclear, chemical and other industries use lot of water (about 30 % of all abstracted water) for cooling purposes and the used hot water is discharged into rivers, streams or oceans.
· The waste heat from the boilers and heating processes increases the temperature of the cooling water.
· Discharge of hot water may increase the temperature of the receiving water by 10 to 15 °C above the ambient water temperature. This is thermal pollution.
· Increase in water temperature decreases dissolved oxygen in water which adversely affects aquatic life.
· Unlike terrestrial ecosystems, the temperature of water bodies remain steady and does not change very much.
· Accordingly, aquatic organisms are adopted to a uniform steady temperature of environment and any fluctuation in water temperature severely affects aquatic plants and animals.
· Hence discharge of hot water from power plants adversely affects aquatic organisms.
· Aquatic plants and animals in the warm tropical water live dangerously close to their upper limit of temperature, particularly during the warm summer months.
· It requires only a slight deviation from this limit to cause a thermal stress to these organisms.
· Discharge of hot water in water body affects feeding in fishes, increases their metabolism and affects their growth.
· Their resistance to diseases and parasites decreases.
· Due to thermal pollution biological diversity is reduced.
· One of the best methods of reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body .