Chapter 17: Sources Of Pollution
The bus halts at a red light and twenty horns start at once. On the pavement, a mechanical breaker is chewing through concrete, and a loudspeaker tied to a pole is announcing a shop sale over the top of it. Behind the row of flats, a small metal works has been running since morning on the ground floor of a residential building. At the edge of the colony, a heap of household refuse is burning slowly, sending a thin grey line into the air. Water from every kitchen and bathroom in the colony runs into a municipal drain, and the drain runs into the river a few kilometres away. Beyond the last houses, smoke drifts across the fields from crop residue burning after the harvest. Every one of these is a source of pollution, but they are not the same kind of source. Some you can walk up to, point at, measure and shut down. Others have no single place at all — they are spread across a hundred fields, ten thousand vehicles and a whole city’s drains, and no inspector can switch them off. That difference decides what can be done about them.
Diagram
Fig. 17.A1 Caption: Sources of pollution in one city scene, some easy to point at and some spread across the whole picture. Brief: A single wide urban scene with rural edge — traffic at a signal, a construction site, a small factory in a residential block, a loudspeaker, a burning refuse heap, a drain running to a river, smoke over distant fields; label each source, arrows pointing away from each source into air or water, and mark which sources sit at one identifiable spot and which are spread out.
17.1 Point And Non-Point Sources Of Pollution
Pollution does not occur in only one form. It appears wherever waste matter or waste energy enters a part of the environment and makes it unfit for the life that depends on it.
This chapter deals with five forms of pollution, each named after the part of the environment that receives the pollutant. (a) Noise pollution enters the air as unwanted sound. (b) Air pollution enters the atmosphere as gases and fine solid matter. (c) Water pollution enters rivers, lakes and the sea through drains and discharges. (d) Soil pollution enters the ground, where the pollutant stays in the material that plants grow in. (e) Radioactive pollution enters air, water and soil alike as radiation and as radioactive matter.
Two Kinds Of Source
Whatever its form, a pollutant has to be released from somewhere, and every release belongs to one of two kinds of source.
Point sources are direct sources of pollutants. The pollutant leaves from one fixed, identifiable place, so it is easy to identify, monitor and control. Non-point sources are indirect sources. The pollutant does not leave from any single outlet but from a large number of scattered places at once, and such sources are therefore difficult to control. What the two share is the pollutant itself: the same gas, the same waste, the same sound may come from either. The difference is not in what is released but in where the release happens, and that difference decides how much can be done about it.
Why The Difference Decides The Remedy
A point source can be walked up to. An instrument can be fixed at its outlet, a reading can be taken at intervals, and a limit can be set for that one outlet and checked against the reading. If the limit is crossed, there is a single place to act on.
A non-point source offers no such outlet. There is nothing to stand an instrument beside, because the release is spread over an area rather than concentrated at a spot. Control has to work indirectly, by changing the practice that causes the release across the whole area, which is slower and much harder to enforce.
The chapter now takes each form of pollution in turn and traces it back to the sources that produce it.
Flowchart
Fig. 17.A2 Caption: Every form of pollution is released either from one identifiable place or from many scattered ones. Nodes: pollution → noise pollution / air pollution / water pollution / soil pollution / radioactive pollution → each of these five branches again into two: point sources (direct, one fixed outlet, easy to identify, monitor and control) and non-point sources (indirect, release spread over an area, difficult to control)
17.2 Noise Pollution
Noise pollution is unwanted sound that produces unpleasant effects and discomfort. Sound is not noise merely because it is loud. It becomes unwanted when it interferes with normal activities such as sleeping or conversation, or when it disrupts a person’s quality of life.
This makes noise pollution different from the other forms in this chapter. Nothing solid is left behind and nothing is added to the air that can be collected in a jar. What is released is energy, and it does its damage while it is being produced. The moment the source stops, the pollution stops with it, which is why the argument is always about the source rather than about cleaning up afterwards.
Fig. 17.1 gathers the main sources of noise pollution around a single centre, and the sections that follow take them one at a time.
Diagram
Fig. 17.1 Caption: Sources of noise pollution. Brief: Redraw the book’s wheel figure — a central circle labelled ‘Noise Pollution Sources’ with eight coloured circles around it, labelled traffic, factories, construction sites, airports, agricultural equipment, household sounds, defence and loudspeakers; arrows running from each outer circle inward to the centre.
17.2.1 Sources Of Noise Pollution
Noise From Traffic
The rapidly increasing number of vehicles on the roads is a big source of noise pollution. The noise does not come from the engines alone. Increasing traffic jams in congested areas lead to repeated hooting of horns by impatient drivers, and it is this hooting that turns a busy road into a noisy one.
Traffic noise is also the clearest everyday example of a non-point source. No single vehicle can be blamed and no single outlet can be fitted with a control, because the sound is produced by thousands of moving vehicles at once.
Noise From Factories
Factories produce a great deal of noise pollution. Textile mills, printing presses, engineering establishments and metal works contribute heavily towards it, because each of them runs heavy machinery for long hours at a stretch.
The trouble is made worse by where these factories stand. In industrial cities the industrial zones are often located within the residential zones of the city, especially in the case of small scale industries. These factories are usually located on the ground floors of residential buildings, so the noise reaches the people living directly above and around them, causing annoyance, discomfort and irritation to residents who cannot get away from it.
The situation is quite different in modern planned cities such as Chandigarh, in northern India, where the whole layout of the city was decided before it was built. There the industrial area is kept away from the residential area, and the two are separated from each other by a sufficiently wide green belt — a strip of open, planted land on which no building is allowed. The distance and the belt of trees between them mean the noise never reaches the homes at full strength.
Noise From Construction Sites
Noise from construction sites is generally far worse than noise originating from factories. There are two reasons for this. Construction itself causes high noise emissions, and the equipment used is inherently noisy — it is built to break, drill and move heavy material, and it cannot do that quietly.
In the era of fast urbanisation, demolition and repair activities add to this. The huge machines used for these purposes create a great deal of noise, to the annoyance of the people living near the sites of construction. A factory at least stands in one place and can be built with its noise in mind; construction arrives beside people who were already living there.
Noise From Loudspeakers
In India loudspeakers are often used during religious functions, at births, marriages, elections and demonstrations, and for commercial advertising. Loudspeakers are therefore a major source of noise pollution.
A loudspeaker is a source of a particular kind, because the noise is not a by-product of some other work. The whole purpose of the equipment is to make sound travel further than it naturally would, and to reach people who never chose to listen.
Noise From Aircraft And Airports
Noise pollution caused by airplanes has been increasing steadily during recent years, especially in the areas close to international airports. The problem has mainly arisen because of the widespread use of heavy long-range jet aircraft.
Noise made by jet planes is more disturbing than that of the old propeller driven aircraft, because it is of far higher pitch. Jet noise is caused by the violent mixing of the jet of gases from the engine with the surrounding air. It is at maximum level during take-off, when the engine delivers maximum thrust, and it reduces rapidly as the aircraft climbs away from the ground.
Landing works the other way. During landing, the main source of high-frequency noise is the sound made by the air compressor and the turbine blades. 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.
Diagram
Fig. 17.A3 Caption: Take-off noise is intense and short-lived, while landing noise is less intense but lasts far longer over the ground. Brief: Two side-by-side profiles of an aircraft path over a row of houses — take-off rising steeply away from the runway with a short, deep band of noise marked below it, landing approaching in a long low path with a longer, shallower band of noise marked below it; label the sources as jet of gases mixing with air at take-off and air compressor and turbine blades at landing; arrows show direction of flight.
17.2.2 Other Sources
Besides the sources described above, noise pollution comes from four further groups of sources. (a) Household sources produce many indoor noises, such as the banging of doors, the noise of playing children, the crying of infants and the moving of furniture. Entertainment equipment such as radios, record-players and television sets adds to it, as do domestic gadgets like mixer-grinders, pressure cookers, desert coolers, air-conditioners, exhaust fans, vacuum cleaners, and sewing and washing machines. (b) Agricultural equipment generates noise during usage, including tractors, thrashers, harvesters, tube wells and powered tillers. (c) Defence activity adds a great deal of noise pollution to the atmosphere through artillery, tanks, the launching of rockets, explosions, the exercising of military airplanes and shooting practices. The screams of jet engines and sonic booms — the sharp crack heard on the ground when an aircraft passes overhead at very high speed — have a deafening impact on the ears, and in extreme cases have been known to shatter window panes and old dilapidated buildings. (d) Miscellaneous sources include the noise from automobile repair shops, and from blasting, bulldozing and stone crushing.
Household noise is worth a second look, because it is the one group on this list that a person creates for themselves. It shows that noise pollution is not only something done to people by factories and aircraft. Every gadget that saves labour does so by putting a motor in the room, and a motor makes sound.
17.3 Air Pollution
Air pollution is the contamination of air by pollutants like dust, smoke and harmful gases, which cause adverse effects on human beings, plants, animals and the environment. The air itself is not changed into something else. Matter is added to it that does not belong there, and the mixture we breathe is no longer the clean mixture the atmosphere would hold on its own.
Air pollutants are so varied that no single list can hold them in a useful order. They are therefore classified in three different ways, and each way asks a different question of the same pollutant: where did it come from, what state is it in, and who released it. Fig. 17.2 sets out the three classifications together.
Diagram
Fig. 17.2 Caption: Air pollution classified in three ways — by origin, by state of matter and by source. Brief: Redraw the book’s circular figure — a central circle labelled ‘Air Pollution’ with an outer ring divided into three labelled arcs, origin, state of matter and sources; inside the ring, six segments paired to their arc, primary pollutants and secondary pollutants under origin, gaseous and particulate under state of matter, natural and man-made under sources.
17.3.1 According To Origin
The first classification asks whether the pollutant came out of the source in the form we find it in.
Primary pollutants are the pollutants that are emitted directly from the sources and are found in the atmosphere in the form in which they are emitted. Ash, smoke, dust, radioactive compounds and the oxides of sulphur and nitrogen are all primary pollutants: whatever left the chimney or the exhaust is what the air now holds.
Secondary pollutants are the pollutants that are formed in the atmosphere by chemical interactions between primary pollutants and atmospheric constituents. Sulphur trioxide, ozone, Peroxyacetyl Nitrate (PAN) and ketones are examples. No source releases them. They are made in the air after the release, out of substances that were released.
This distinction matters for control. A primary pollutant can be traced back to the outlet it came from and stopped there. A secondary pollutant has no outlet of its own, and the only way to reduce it is to reduce the primary pollutants that go on to form it.
Flowchart
Fig. 17.A4 Caption: Secondary pollutants are not released by any source; they are made in the air out of what was released. Nodes: source → primary pollutants emitted directly (ash, smoke, dust, radioactive compounds, oxides of sulphur and nitrogen) → mix with atmospheric constituents → chemical interaction in the atmosphere → secondary pollutants formed (sulphur trioxide, ozone, Peroxyacetyl Nitrate, ketones)
17.3.2 According To State Of Matter
The second classification asks what physical state the pollutant is in as it travels through the air.
Gaseous air pollutants are those that exist in a gaseous state at normal temperature and pressure. They include carbon dioxide (CO₂), the nitrogen oxides (NOₓ) and the sulphur oxides (SOₓ). Being gases, they spread through the air and cannot be filtered out of it by anything as simple as a cloth.
Particulate air pollutants are not gaseous substances. They are suspended droplets, solid particles, or mixtures of the two, and they include dust, fumes, smoke, soot and fly ash. Being matter in solid or liquid form, they eventually settle out of the air onto surfaces, which is why they can be seen on a windowsill in a way that a gas never can.
17.3.3 According To Sources
The third classification asks who or what released the pollutant.
Natural sources release pollutants without any human hand in it. They include volcanic eruptions, the deflation of sand and dust — the lifting and carrying away of loose material by wind — as well as forest or wild fires of natural vegetation.
Man-made sources are human activities. They include activities related with industries, urban centres, aircraft, nuclear experiments, automobiles, agriculture and power plants.
The difference is not in the pollutants themselves. A wild fire and a burning refuse heap put much the same smoke into the air. The difference is that a natural source can only be prepared for, while a man-made source can, in principle, be changed. Fig. 17.3 shows a fire in natural vegetation, one of the natural sources listed above.
Diagram
Fig. 17.3 Caption: Forest fire. Brief: Photograph of a fire burning through natural vegetation on open ground, flames and a thick plume of smoke rising, to be sourced; label the smoke plume as pollutants entering the atmosphere from a natural source.
17.4 Sources Of Air Pollution
Many types of pollutants are released into the air from various sources. The major man-made sources of air pollution are automobiles, industries, the burning of garbage, and brick kilns. Between them these sources release oxides of carbon, oxides of sulphur, oxides of nitrogen, hydrocarbons, ozone and chlorofluoromethanes, among others.
The list is worth reading slowly, because the same few sources keep returning under different pollutants. A city does not have a separate cause for each gas in its air. It has a small number of activities, each releasing several pollutants at once. Fig. 17.4 shows two of them at work.
Diagram
Fig. 17.4 Caption: Sources of air pollution — vehicular exhaust on a city road, and building material production. Brief: Two photographs side by side, to be sourced; the first showing traffic at a road junction with exhaust smoke around the vehicles, labelled ‘Vehicular Pollution’, the second showing building material being handled with dust rising from the heap, labelled ‘Building Material Production’.
17.4.1 Vehicular Pollution
Vehicles are mainly responsible for more than 80 per cent of total air pollution. The major pollutants released from automobiles, locomotives, aircraft and the like include carbon monoxide (CO), unburnt hydrocarbons and nitrogen monoxide. Each of these comes out of the exhaust because the fuel has not burnt completely, or because the heat of the engine has made the nitrogen and oxygen of the air combine.
In the major metropolitan cities of Delhi, Mumbai and Kolkata, vehicular exhaust accounts for 75 per cent of all CO, 45 per cent of all hydrocarbons, 40 per cent of all oxides and 30 per cent of all suspended particulate matter.
The four shares do not rise and fall together, and that is the useful part. Vehicles dominate the carbon monoxide in a metro’s air, so removing vehicles from a road would clear most of it. They contribute less than a third of the suspended particulate matter, so the same step would leave most of the dust untouched, because it is coming from elsewhere. A single figure for pollution from vehicles would have hidden all of this; the pollutant has to be named before the share means anything.
Hydrocarbons And The Making Of Smog
Air pollution is also caused by gaseous and volatile hydrocarbons such as methane, acetylene and ethylene. Some hydrocarbons like ethylene undergo chemical reactions in the presence of sunlight and nitrogen oxide to form photochemical oxidants, such as ozone, that are harmful. Fuel combustion in automobiles also produces nitrogen dioxide.
These lead to the formation of smog, a hanging mixture of smoke and fog that sits over a city instead of dispersing. In some cities like Delhi, smog severity is aggravated by stubble burning in neighbouring agricultural areas, where crop residue left after the harvest is set alight and the smoke drifts in.
Smog is harmful for health, as it causes asthma, bronchitis, shortness of breath, and eye and nose irritation. It also reduces visibility, and so leads to problems in traffic movement — the traffic that helped create it then moves more slowly through it.
Flowchart
Fig. 17.A5 Caption: Sunlight turns two ordinary exhaust pollutants into a third one that no engine ever released. Nodes: fuel burnt in automobiles → unburnt hydrocarbons such as ethylene released + nitrogen oxide released → sunlight falls on the mixture → chemical reaction in the air → photochemical oxidants formed, including ozone → these, with smoke and fog, build up as smog → reduced visibility and traffic problems; and → asthma, bronchitis, shortness of breath, eye and nose irritation
17.4.2 Industrial Pollution
Industries such as chemical industries, paper and pulp mills, cotton mills and petroleum refineries produce most air pollution. Cement factories emit dust, which is a potential health hazard for anyone working or living near them.
The smoke coming out from factories is not simply a dark gas. It carries small particles of dust, carbon, metals, and other solids, liquids and radioactive materials, which get mixed in the smoke and pollute the air. Whatever the process inside uses, some of it leaves through the chimney.
From Coal To Acid Rain
The burning of sulphur in coal or heavy oil in thermal power plants releases sulphur dioxide (SO₂) into the air. Sulphur dioxide then combines with oxygen and water to form sulphuric acid (H₂SO₄) in the atmosphere. The acid is a health hazard, and besides that, it produces acid rain.
This is a secondary pollutant at work, of the kind described earlier in the chapter. Nothing releases sulphuric acid from a chimney. What is released is sulphur dioxide, and the atmosphere itself supplies the oxygen and the water that turn it into an acid before it falls. Fig. 17.5 shows what that fall does to the leaves it lands on.
Diagram
Fig. 17.5 Caption: Effects of sulphur dioxide on leaves. Brief: Photograph of leaves on a plant showing pale yellow and brown blotching between the veins, to be sourced; label two or three damaged patches and keep one healthy green leaf in frame for comparison.
Why Winter Is Worse
Kanpur, an industrial city on the Ganga plain in Uttar Pradesh, has the heaviest air pollution due to the dust and smoke of its factories. In winter, smog, a combination of smoke and fog, envelopes many cities, creating health hazards and traffic problems.
Winter adds to the load rather than removing it. During the winter months, because of severe cold, the use of coal and fossil fuels to heat homes and for other purposes increases, so more smoke enters the air at exactly the season when fog is already there to hold it.
17.4.3 Burning Of Garbage
Burning of garbage pollutes the atmosphere by emitting such gases as carbon dioxide, sulphur dioxide and nitrogen oxides, along with particulate matter such as dust and smoke. The open burning of refuse and burning in municipal incinerators are both responsible for air pollution.
Biomass burning, such as forest fires, produces nitrogen dioxide (NO₂) in the atmosphere. Nitrogen dioxide is readily soluble in water and forms nitric acid, which falls out in the rain. Here again the pollutant that reaches the ground is not the one that left the fire.
Burning is also the reason a heap of waste is so hard to regulate. A chimney has an owner and a fixed place; a refuse fire at the edge of a colony has neither, which is what puts it among the non-point sources described at the start of this chapter.
The pollutants discussed so far, and the sources each of them comes from, are brought together in Table 17.1.
17.5 Sources Of Water Pollution
The sources of water pollution can be divided into two categories, domestic and industrial. The division is useful because the two put very different things into the same river, and neither can be cleaned up by the method that works on the other.
17.5.1 Domestic
People use water for drinking, for the preparation of food, for bathing and for cleaning the house. Almost none of that water is used up. Most of the used water is drained out through municipal drains and poured into a river or a lake, which means the river receives whatever the household put into it.
By the time it leaves the colony, that water is carrying more than soap. Domestic wastewater that is mixed with other wastes such as plastic, detergents, animal dung and human faecal material is known as municipal waste.
Phosphates And The Green Lake
Many detergents and fertilisers contain phosphates. When phosphates are discharged into waterways, their remnants promote the rapid growth of algae, because a phosphate is a plant nutrient and the algae now have more of it than the water would ever naturally hold.
This enrichment process is known as eutrophication. Aquatic weeds multiply rapidly in many water bodies as a result, and once they cover the surface they interfere with fishing, with navigation and with irrigation. A drain that carried nothing more sinister than washing water has changed what can be done on the water it emptied into.
Flowchart
Fig. 17.A6 Caption: A nutrient meant for crops and for cleaning becomes a nutrient for algae once it reaches open water. Nodes: detergents and fertilisers containing phosphates → used in homes and on fields → discharged into waterways through municipal drains → phosphate remnants enrich the water → rapid growth of algae, called eutrophication → aquatic weeds multiply rapidly → fishing, navigation and irrigation obstructed
17.5.2 Industrial
Industries dealing with chemicals, with pulp and paper, and with food processing produce waste material such as heavy metals or synthetic organic compounds. Heavy metals are metals that stay in the body once taken in, instead of passing out of it.
This waste reaches water bodies in two ways. It arrives either through direct discharge, where an outlet empties into the water, or by leaching from waste dumps, where rain soaks through a heap of waste, dissolves what is in it, and carries it down into the water below. The first is a point source that can be found and measured; the second has no outlet at all. Fig. 17.6 shows the first kind at work.
Diagram
Fig. 17.6 Caption: Effluents from factories cause water pollution. Brief: Photograph of factory buildings behind an open channel carrying discoloured effluent across bare ground, to be sourced; label the outfall point and the direction of flow away from the factory.
The Heavy Metals
Among the heavy metals, cadmium, lead, mercury, copper and chromium get into water. Three of them are worth setting out in detail. (a) Lead is used in many industries and may accumulate in the biological system rather than passing through it. (b) Lead can enter water from many sources, such as the mining and smelting of lead-bearing ores and metals, lead plumbing, paints and ceramic glazes, and the disposal of lead-zinc batteries in the garbage. (c) Manganese has been found widely in nature and is used in manufacturing steel. (d) Mercury is used in plastic and chemical industries, and methyl mercury is the most common form of mercury found in the aquatic environment.
The mercury figure is the one to hold on to. It has been reported that the accumulation of mercury is as high as 5000 times the amount in fish, and that it is passed on to man. The metal does not stay where it was discharged. It moves into the living things in the water, builds up in them, and travels on to whoever eats them, which is why a factory outlet can reach a person who has never been near the factory.
17.6 Sources Of Soil Pollution
Soil pollution is the result of several sources, which can be categorised under three heads. (a) Chemical fertilisers, added to farmland to raise the nutrient content of the soil. (b) Biomedical waste, dumped on or into the ground after use. (c) Pesticides, sprayed on the farm to kill the pests and weeds growing there.
Soil is the slowest of the four receivers in this chapter. Air moves, and a river carries its load away, but soil stays where it is. Whatever is put into a field remains in that field, and each season’s addition is laid on top of the last one.
Chemical Fertilisers
Agricultural practices today use chemical fertilisers, which contain such plant nutrients as nitrogen, phosphorous and potassium. These are the three nutrients a growing crop draws most heavily from the soil, which is why they are the three that are put back.
The excessive use of chemical fertilisers creates pollution. The fertilisers are used to enrich the soil, but they also contaminate the soil with their impurities — the substances that come along with the nutrient and are of no use to the plant.
The damage does not stop at the soil. When the fertilisers are contaminated with other synthetic organic pollutants, the water in the soil gets polluted, and that water is the same water a root draws on and a well later reaches.
Biomedical Waste
Biomedical waste is the waste left behind by hospitals. It contains organic materials, chemicals, metal, needles and plastic, so a single dump can carry sharp objects, chemical residues and living matter all at once.
The dumping of domestic sewage and of hospital organic wastes contaminates the soil with pathogens — the organisms that cause disease — and these affect human health. The excreta of humans and of animals pollute the soil in the same way.
Where this waste is not collected and treated, intestinal parasites constitute the most serious soil pollution problem, and that burden falls hardest in the poorer countries of the world. The reason is not the soil there but the sanitation available to the people living on it.
Pesticides
Pesticides and weedicides are used to control pests and weeds on the farm — the first kill the insects and other animals that attack a crop, the second kill the plants competing with it. Both are applied to the field on purpose, and both contaminate the soil.
Pesticide residues change the chemical properties of the soil. They accumulate in the soil permanently, which means each spraying adds to what is already there rather than replacing it, and they introduce these toxic materials into plant products.
That last step is what makes a pesticide different from most other soil pollutants. It is designed to be taken up by living tissue, so once it is in the soil there is nothing to stop the crop taking it up as well.
Flowchart
Fig. 17.A7 Caption: A chemical sprayed to protect the crop ends up inside the crop it protected. Nodes: pesticide or weedicide sprayed on the farm → pests and weeds controlled → residues left in the soil → chemical properties of the soil changed → residues accumulate permanently, each spraying adding to the last → toxic materials introduced into plant products
17.7 Sources Of Radioactive Pollution
Radioactive pollution is the odd one out in this chapter. What is released cannot be seen, smelt or heard, and the material carrying it looks no different from ordinary dust or water. There are two main sources of it, one natural and one man-made.
17.7.1 Natural Sources
The natural sources are cosmic rays, energetic radiations reaching the earth from outer space. They arrive continuously, and nothing on the ground produces them.
Though they are a major hazard in space, they are not dangerous for organisms on earth. This is why the sources that matter for pollution on the ground are the man-made ones, and why the rest of this section is given to them.
17.7.2 Man-made Sources
Four kinds of human activity cause radioactive pollution.
X-Rays Waste
The use of X-rays is common for detecting skeletal disorders — the doctor uses them because they pass through soft tissue and show the bone beneath. Cancer patients undergo radium and other isotope radiations as part of their treatment.
The same property that makes the radiation useful makes it dangerous. The X-rays pass through genetic cells and affect the chromosomes, the structures that carry the instructions passed on to the next generation of cells, and the result is mutations, or changes in those instructions.
Radioactive Fallout From Nuclear Plants
In a nuclear power establishment, both the fuel elements and the coolants are sources of radiation pollution. The fuel is radioactive to begin with, and the coolant becomes radioactive by circulating around it.
Radioactive wastes from atomic reactors are hazardous to living organisms, and they are difficult to put anywhere. Even if radioactive wastes are buried underground, they may escape into the surroundings, and inert gases — gases that take part in no chemical reaction and so cannot be locked into any solid — escape as vapours and pollute the environment. Fig. 17.7 shows the towers of such an establishment.
Diagram
Fig. 17.7 Caption: Nuclear reactors. Brief: Photograph of a nuclear power establishment showing the cooling towers with vapour rising and a tall chimney alongside, to be sourced; label the cooling towers and keep the whole plant boundary in frame.
Nuclear Weapons
The testing of nuclear weapons involves using radioactive substances like Uranium 235 and Plutonium 239 for fission, the splitting of heavy atoms that releases the energy of the weapon.
The pollution does not end with the test itself. The radioactive waste emitted during these tests makes the surrounding materials radioactive, so ordinary soil, dust and structures near the site become sources in their own right.
Where The Fallout Travels
Radioactive particles are carried away to distant places by wind, so the pollution does not stay near the place it was released. They are brought down by rain, and raindrops containing these radioactive particles fall on the earth and affect the soil, causing soil pollution.
From the soil, the radioactive materials reach water sources. There the aquatic organisms absorb and accumulate them through the food chains, and pass them on to human beings. A single release therefore travels through air, soil, water and living tissue in turn, which is why radioactive pollution cannot be treated as a problem of one medium alone.
Flowchart
Fig. 17.A8 Caption: One release travels through air, rain, soil, water and living things before it reaches a person. Nodes: radioactive material released from a nuclear test or plant → radioactive particles carried to distant places by wind → brought down by rain → raindrops fall on the earth → soil polluted → radioactive materials reach water sources → aquatic organisms absorb and accumulate them → passed along the food chains → passed on to human beings
Radioactive Isotopes
Radioactive isotopes — forms of an element that are radioactive — are used in research laboratories. The waste from that work leaves the laboratory in its wastewater.
When the wastewater from these laboratories reaches the rivers, streams and lakes through the sewers, it causes water pollution. The laboratory is a point source, and the sewer is the direct route from it to the river.
17.8 Summary
- Pollution occurs in five forms — noise, air, water, soil and radioactive — each named after the part of the environment that receives the pollutant.
- Every form of pollution has two kinds of source, and the difference decides what can be done about it.
- Point sources are direct sources, releasing from one fixed place, and are easy to identify, monitor and control.
- Non-point sources are indirect, releasing from many scattered places at once, and are therefore difficult to control.
- Noise pollution is unwanted sound that produces unpleasant effects and discomfort, and sound becomes unwanted when it interferes with sleeping or conversation or disrupts a person’s quality of life.
- The main sources of noise pollution are traffic, factories, construction sites, loudspeakers and airports.
- Traffic noise comes chiefly from the repeated hooting of horns in congested areas.
- Factory noise troubles residents where industrial zones lie inside residential zones, and a planned city avoids this by separating the two with a wide green belt.
- Construction noise is worse than factory noise because construction itself emits high noise and the equipment is inherently noisy.
- Loudspeakers are used at religious functions, marriages, elections, demonstrations and for advertising.
- Jet aircraft are loudest at take-off, but landing noise lasts longer because the aircraft stays low over the ground.
- Other sources of noise pollution are household activity and gadgets, agricultural equipment, defence activity, and miscellaneous sources such as repair shops, blasting, bulldozing and stone crushing.
- Air pollution is the contamination of air by pollutants like dust, smoke and harmful gases that adversely affect human beings, plants, animals and the environment.
- Air pollutants are classified in three ways, and every pollutant carries an answer under all three.
- By origin, into primary pollutants, emitted directly in the form found, and secondary pollutants, formed in the atmosphere by chemical interaction.
- By state of matter, into gaseous pollutants and particulate pollutants such as dust, fumes, smoke, soot and fly ash.
- By source, into natural sources such as volcanic eruptions and wild fires, and man-made sources such as industries, automobiles and power plants.
- The major man-made sources of air pollution are automobiles, industries, the burning of garbage, and brick kilns.
- Vehicles are mainly responsible for more than 80 per cent of total air pollution, releasing carbon monoxide, unburnt hydrocarbons and nitrogen monoxide.
- Hydrocarbons such as ethylene react with nitrogen oxide in sunlight to form photochemical oxidants like ozone, which build up as smog.
- Industries release dust and smoke carrying solids, liquids and radioactive materials, and sulphur dioxide from coal turns into sulphuric acid and acid rain.
- Burning garbage emits carbon dioxide, sulphur dioxide, nitrogen oxides and particulate matter, and nitrogen dioxide from biomass burning returns as nitric acid in rain.
- Water pollution comes from two categories of source.
- Domestic sources send municipal waste through drains into rivers and lakes, and phosphates from detergents and fertilisers cause eutrophication, the rapid growth of algae and weeds.
- Industrial sources add heavy metals and synthetic organic compounds by direct discharge or by leaching from waste dumps.
- Soil pollution arises from chemical fertilisers, biomedical waste and pesticides, and what enters the soil stays there and builds up season by season.
- Radioactive pollution has natural sources in cosmic rays, which are not dangerous for organisms on earth, and man-made sources in X-rays waste, fallout from nuclear plants, nuclear weapons testing and laboratory isotopes.
- Radioactive particles travel by wind, come down in rain, pollute the soil, reach water sources, and are accumulated by aquatic organisms and passed along food chains to human beings.
Flowchart
Fig. 17.A9 Caption: The whole chapter in one chain — an activity releases a pollutant, and the pollutant then moves between air, water, soil and living things. Nodes: natural events or human activity → release from a point source (one fixed outlet, easy to monitor and control) or from a non-point source (scattered, difficult to control) → the pollutant enters air, water or soil, or is released as noise energy → in the air, primary pollutants may react with atmospheric constituents to form secondary pollutants such as ozone, sulphuric acid and nitric acid → wind carries particles to distant places and rain brings them down → soil receives them and passes them to water sources → aquatic organisms absorb and accumulate them → passed along food chains to human beings → back to the activity that released them, which is the only point at which the chain can be broken
What This Chapter Cannot Tell You
This chapter names sources; it does not weigh them. Table 17.1 lists which sources release which pollutant, but not how much each contributes, and it carries no year, so it cannot show whether any source has grown or shrunk.
The shares given for vehicular exhaust hold for three metropolitan cities and for four named pollutants only. They say nothing about a small town, a village or any other pollutant, and a figure for a whole city still hides the difference between one road and the next.
Naming a source is also not the same as measuring the harm it does or knowing what would reduce it. Those questions are asked elsewhere; here the work was to follow each pollutant back to where it came from.
17.9 Check Your Concepts
Study Table 17.1.
- Which source appears against the largest number of pollutants in the table?
- State one thing the table does not tell you about these sources.
Small factories in many industrial cities cause annoyance to residents, while the same kind of work causes no such complaint in a planned city like Chandigarh. Explain why, and state what would have to change for the complaint to return.
In the major metropolitan cities, vehicular exhaust accounts for 75 per cent of all carbon monoxide and 30 per cent of all suspended particulate matter.
- Work out the share contributed by all other sources together in each case.
- Using your answer, explain why taking vehicles off a road would clear one of these pollutants far more than the other.
A radioactive particle is released during the testing of a nuclear weapon. Trace, in order, the steps by which it can reach a human being who lives far from the test site.
Look at the two scenes in Fig. 17.4. For each scene, list the main pollutants being released and identify which type of pollution it causes. Give reasons to support your answers.
What is known as smog? What harm is done by smog, especially in winter?
In cities, flyovers are built with large sheets of fibre glass fixed along their outer sides. Give the reason for this.
With reference to noise pollution, answer the following:
- When does sound become a source of noise pollution?
- How does traffic contribute to noise pollution?
- Why are construction sites considered worse than factories in their contribution to noise pollution?
- How do airplanes cause noise pollution, and why is there more noise pollution during landing than during take-off?
Air pollution is the contamination of air by pollutants. In this context, answer the following:
- Based on their origin, how can air pollutants be classified?
- How does the use of automobiles cause air pollution?
- How do industries pollute the air?
- Name any three air pollutants and two sources of each.
With reference to the sources of water pollutants, answer the following:
- What are the domestic sources of water pollution?
- Why is it harmful to dispose of household detergents in water bodies?
- In what way does industrial waste pollute water?
- What are the sources of radioactive pollution? Describe each of them.