Chapter 18: Effects of Pollution
A monument does not usually have an enemy you cannot see. The Taj Mahal stands in Agra, on the bank of the Yamuna, and it is built of marble — a stone that takes a polish so fine it seems to glow at first light. For most of its life that surface held. Then it began to change: it dulled, it discoloured, and in places the polished skin corroded away. Nothing had touched it. What reached the stone came out of the air. Sulphur dioxide, released when fuel burns, drifts into the atmosphere and meets moisture there. The two combine to form sulphuric acid, which comes down in rain and mist and settles on the marble. The acid then attacks the stone, discolouring it and eating into it grain by grain. The damage is done by a chemical no visitor can see, assembled in the sky above the city. That is the pattern this chapter follows. Pollution rarely stays where it is made. It travels through air, water, soil and the food chain, and it lands somewhere else — on a building, in a lung, in a lake, inside a fish. What follows is an account of where it lands, and what it does when it arrives.
Diagram
Fig. 18.A1 Caption: Sulphur dioxide in the air becomes acid in the rain, and the acid attacks the marble. Brief: Cross-section from sky to stone — label sulphur dioxide rising from burning fuel, moisture in the air, sulphuric acid forming, acid rain falling, and a discoloured and pitted marble surface below; all arrows point downward from air to stone.
18.1 Pollution And Its Effects
Pollution is not one problem but five, and each one travels by a different route. This chapter deals with all five, and the list below is the order in which they are taken up. (a) Noise pollution travels as sound through the air, and reaches anything that can be shaken by it. (b) Air pollution travels as gases and fine particles carried by the air itself. (c) Water pollution travels through rivers, lakes and seas, and through everything that lives in them. (d) Soil pollution travels through the ground, and reaches us mainly through the crops grown in it. (e) Radioactive pollution travels as radiation from radioactive material, and through the food chain that material enters.
Whichever route it takes, pollution has an impact on all living organisms and on their environment. The pollutants — the harmful substances or forms of energy released into the surroundings — are what actually do the damage. They are responsible for environmental degradation, meaning a steady lowering of the quality of air, water, soil and living things in an area, so that the environment supports life less well than it did before.
The Range Of Effects
The effects on human beings do not all arrive at the same strength or at the same speed. They cover a wide range. (a) At the mild end there is discomfort — the irritation and disturbance a person notices at once but recovers from. (b) At the severe end there are long term effects such as cancer and physical deformities, which appear only after years of exposure. (c) Increased pollution also causes psychological and behavioural disorders, so the harm is not confined to the body.
This range is worth holding on to, because it explains why pollution is easy to ignore. The effects a person feels immediately are usually the small ones, while the serious ones build quietly over years.
Flowchart
Fig. 18.A2 Caption: A pollutant is released in one place and does its damage in another. Nodes: pollutant released → enters the environment → air / water / soil → carried away from its source → acts on the environment, and on living organisms → mild discomfort, or long term illness after years of exposure → environmental degradation
The rest of the chapter takes each type of pollution in turn. For every one, the effects on the environment are set out first, and the effects on human beings after that.
18.2 Effects Of Noise Pollution
The effects of noise pollution are multifaceted and interrelated, which means they show up in many different forms and each one feeds into the others. A person who cannot sleep is also a person who is tired at work, and a tired worker in a noisy factory is a worker more likely to have an accident. Noise pollution has ill effects not only on human beings but also on the environment around them.
Sound level is measured in decibels, written dB. The numbers matter in this chapter, because the chapter itself marks out where the harm begins: below about 90 dB there is little physical effect, while continuous levels above about 100 dB begin to damage the ear. The chart below sets out the three directions in which those effects travel.
Flowchart
Fig. 18.A3 Caption: Noise damages the environment, human health and animal life, each in its own way. Nodes: noise pollution → effects on the environment: cracks in monuments, cracks in hills, broken glass panes, vibration in buildings / effects on human health: hearing loss, disturbed communication, disturbed sleep, mental and physical illness / effects on animals: migration avoided, miscarriage in mammals and fishes, birds stop laying eggs
18.2.1 Effects On Environment
Sound is a vibration travelling through the air, and a vibration strong enough will shake whatever it reaches. This is why noise damages structures that were never meant to move. (a) Noise booms cause cracks in national and archaeological monuments, which are often built of old stone that has already weathered. (b) Very high levels of noise are the cause of cracks in hills. (c) High intensity explosions can break glass panes and cause vibrations in buildings.
18.2.2 Effects On Human Health
Noise reaches human beings through the ear, but the harm does not stop at the ear. The effects on human health may be set out under five heads. (a) Effect on hearing or deafness. Continuous exposure to noise levels above 100 dB has an adverse effect on hearing ability within a fairly short time. Many workers exposed to the noise of jet aircraft or very noisy workshops, even for moderate periods, soon develop detectable hearing defects. (b) Effect on communication. External sounds interfere with conversation, with the use of the telephone, and with the enjoyment of radio and television programmes. This affects the efficiency of offices, schools and other places where communication is of vital importance. (c) Interference with sleep. Different people have different depths of sleep, and they can adjust to natural sounds. Noisy conditions near residential areas at night, however, cause real difficulties in sleeping. (d) Mental or physiological effects. Many people complain that noise makes them mentally ill, and experiments have been performed to confirm or disprove these claims. Doctors and scientists have now medically confirmed that noise disturbs living organisms. (e) Effects on physical health and psychological problems. Noise has little physical effect on biological performance provided the noise level is below about 90 dB. Damage to the inner ear may result if continuous noise levels exceed about 100 dB, and this can lead to physical illness.
What The Research Has Found
The fourth of these effects has been studied closely. Fire crackers and other excessive and continuous explosives become physically painful, giving rise to neurosis — a lasting state of anxiety and distress — along with mental illness, cardiovascular diseases, which are diseases of the heart and blood vessels, stomach ulcers and respiratory disorders. Together these reduce human life.
Recent researches have concluded that even short exposures to noise, in excess of about 100 dB, can have adverse effects on the foetus, the unborn baby developing in the womb. They can also cause headache, dizziness and stomach problems.
Psychiatrists and psychologists have in recent researches made observations that noise has a certain relation with physical health. It causes tension, and that tension results in problems such as speech interference, annoyance, fatigue, sleep interference and emotional distress. In industries, noise levels interfere with efficiency and communication, and so raise the possibility of accidents.
The table below sets out what has been observed at particular sound levels, and it is worth reading alongside the two thresholds already given, 90 dB and 100 dB.
18.2.3 Effects On Animals
Human beings can shut a window or leave a noisy street. Animals live in the place they live in, and noise reaches them there. Noise from industries, railways, crackers, explosions, the general commotion of cities and aircraft affects animals, birds, mice, fishes and domestic animals alike.
Two effects have been observed particularly clearly. (a) Birds avoid migrating to places where the noise level is above 100 dB, so a noisy stretch of country can be cut out of a migration route altogether. (b) The noise emissions caused by supersonic aircraft and railways may cause miscarriage in mammals and fishes, and some birds have been found to have stopped laying eggs due to noise pollution.
18.3 Effects Of Air Pollution
Air pollution is the presence in the air of one or more noxious gases and minute particles of solid and liquid matter, in harmful concentrations, of such duration and characteristics that it is injurious to plants, animals, human beings and other materials. The minute solid and liquid particles are called particulates — matter so fine that it stays suspended in the air instead of settling out of it.
That definition is doing more work than it looks. Three separate conditions have to be met before the air is said to be polluted. (a) Something harmful must be present — a noxious gas, or particulates, or both together. (b) It must be present in a harmful concentration, which means enough of it in a given volume of air to do damage. (c) It must stay long enough, and have the character, to injure plants, animals, human beings or materials.
The last two conditions explain why the same gas can be harmless in one place and dangerous in another. Air pollution is a question of how much and for how long, not merely of what is present.
18.3.1 Effects On Environment
The gases that change the environment most are not the ones that smell worst. They are the ones that change how the atmosphere handles heat.
The concentration of carbon dioxide (CO₂) in the air is increasing, and so is the concentration of other greenhouse gases like methane, nitrogen oxide, chlorofluorocarbons and water vapour. These gases trap the earth’s heat instead of letting it escape back to space, and so raise the temperature on the earth. This warming is called global warming, and the chapter sets out six effects it will have on the environment.
How A Warmer Earth Changes
The first two effects are about where and when the extra warmth is felt. (a) Due to global warming, the regions of the Northern hemisphere will heat up more than other areas of the planet, and in temperate mountains the snowlines will melt earlier. A snowline is the level on a mountain above which snow lies through the year, so an earlier melt means the mountain loses its snow cover sooner. (b) Winter and night time temperatures will likely rise more than those of summer and day time, so the warming is felt most at the cold end of the year and the cold end of the day.
The next two are about water leaving the surface. (c) Rising warmth will lead to an increase in the level of evaporation of surface water. The air will also expand, and this will increase its capacity to hold moisture. This in turn will affect water resources, forests and other natural ecological systems, agriculture, power generation, infrastructure, tourism and human health. (d) Due to excessive heat, water will evaporate quickly. Soil that is affected by erosion, and left without any vegetative cover, will not retain moisture for long. Hence there would be droughts.
The last two are about ice and coasts. (e) The rise in temperature would lead to the melting of glaciers. As a glacier slides, it leaves behind mounds of debris and rock, and natural lakes form between them. These lakes are fed by the melting ice faster than the rate at which they can be drained, which unbalances the outflow of water and makes glacier lakes flood more frequently. (f) Deltas will be threatened by flooding, erosion and salt intrusion, which is sea water pushing inland into fresh water and soil. The loss of coastal mangroves — the salt-tolerant forests that fringe such coasts and shelter young fish — will have an impact on fisheries. The major delta area of the Ganga, Brahmaputra and Indus rivers, which has large populations living on it, will be affected by floods, salt water intrusion and land loss.
Flowchart
Fig. 18.A4 Caption: Trapped heat sets off changes on mountains, in soils, on glaciers and along coasts. Nodes: carbon dioxide, methane, nitrogen oxide, chlorofluorocarbons and water vapour build up in the air → the gases trap the earth’s heat → global warming → snowlines in temperate mountains melt earlier / winter and night temperatures rise faster than summer and day temperatures / evaporation of surface water increases and warmer air holds more moisture → water resources, forests, agriculture, power generation, infrastructure, tourism and health affected / eroded and bare soil cannot retain moisture → droughts / glaciers melt and slide → lakes form between mounds of debris → lakes fill faster than they drain → glacier lakes flood more often / deltas flooded, eroded and invaded by salt water → coastal mangroves lost → fisheries affected
Notice that the same rise in temperature produces drought in one place and flooding in another. Heat drives water off the land in the interior and drives ice into the rivers at the source, and the two results meet at the coast, where a delta already close to sea level takes both.
18.3.2 Effects On Human Health
The extent to which human beings are affected by air pollution depends on two things: the duration of exposure and the concentration of the pollutants. A brief brush with dirty air is not the same as breathing it every day, and this is why the table below names the pollutant but cannot by itself tell you how badly a person will be harmed.
Short-Term And Long-Term Effects
Based on this criteria, air pollution has both short-term and long-term effects on human health. The short-term effects appear quickly and usually fade when the person leaves the polluted air. (a) Irritation in the eyes, nose and throat. (b) Respiratory infections such as bronchitis and pneumonia. (c) Headaches, nausea, vomiting, dizziness, convulsions and allergic reactions. (d) Slurring of speech.
The long-term effects are the ones that build up over years of exposure and do not go away. (a) Chronic respiratory disease, meaning disease of the breathing system that lasts a long time. (b) Lung cancer. (c) Cardiovascular diseases and coma. (d) Damage to the nerves, brain, liver and kidneys.
When It All Arrives At Once
Usually the concentration is low and the duration is long. Occasionally the reverse happens, and the chapter gives one instance of it.
Read that case against the two conditions this subsection began with. Bhopal was an extreme concentration acting over a very short duration, and it produced in one night the kind of damage — to the lungs, the nerves and the unborn — that ordinary air pollution takes decades to produce. The figure of 100 sq km matters just as much: the gas did not stop at the factory wall, because air carries whatever is put into it across whatever lies downwind.
Diagram
Fig. 18.1 Caption: Union Carbide factory, Bhopal. Brief: Photograph of the disused pesticide plant at Bhopal — show the rusted towers, pipework and sheds with vegetation grown up around them; no people in frame.
18.3.3 Effects Of Pollutants On Plants
Air pollutants affect the growth of plants and their metabolism by destroying chlorophyll and disrupting photosynthesis. Chlorophyll is the green colouring matter in a leaf, and photosynthesis is the process by which the leaf uses sunlight to make food. Damage the first and you have stopped the second, and a plant that cannot make food cannot grow.
The effects of air pollution on plants are as follows. (a) Sulphur dioxide (SO₂) bleaches the surface of the leaves and causes loss of chlorophyll, which results in yellowing of the leaves, especially in green leafy vegetables. (b) Nitrogen dioxide (NO₂) results in the premature falling of leaves and suppressed growth of plants, and this leads to reduced yield of crops. (c) Ozone damages the leaves of plants. (d) Peroxyacetyl Nitrate (PAN) damages leafy vegetables and causes premature fall, discolouration and curling of sepals. Sepals are the small green parts that enclose a flower bud.
18.3.4 Effects On Animals
Animals are harmed less by breathing polluted air than by eating what has settled out of it. Particulate matter drifts down and coats grass and plants, and the animals that feed on grass and plants take the pollution in with their food. (a) Animals feeding on grass and plants coated with polluted particulate matter are affected with arsenic poisoning. (b) Lead poisoning results in bronchitis and lack of appetite in pet animals.
18.3.5 Effects On Materials
Air pollution does not need anything living to damage. It attacks stone, metal, paper, leather and cloth as readily as it attacks lungs, and the effects on materials may be summarised as follows. (a) Soot, dust and fumes from air pollutants cause damage to painted surfaces, fabrics and buildings. (b) Sulphuric acid mist and acid rain — rain that has turned acidic because acid formed in the air has dissolved in it — damage marble and limestone. The Taj Mahal has suffered damage caused by sulphur dioxide (SO₂) in the atmosphere, and its marble structure is getting discoloured and corroded. (c) Sulphur dioxide (SO₂) together with moisture forms sulphuric acid (H₂SO₄), and this causes corrosion of metals like steel, copper and zinc. (d) Paper becomes brittle, and leather undergoes disintegration, by the action of SO₂ and acid gases. (e) Ozone, SO₂, NO₂ and similar gases discolour and deteriorate textiles, and reduce their strength.
The pattern running through this list is that the harm is chemical rather than physical. Nothing strikes the marble, the steel or the cloth. A gas released somewhere else meets moisture in the air, becomes an acid, and settles on a surface that has no defence against it.
18.4 Effects Of Water Pollution
Water pollution affects man, aquatic animals and the environment alike. It has one feature the other kinds of pollution do not: water carries whatever is put into it, and everything that lives in the water is bathed in it continuously, with no way out.
18.4.1 Effects On Environment — Animals, Marine Life And Vegetation
Due to water pollution, the process of photosynthesis is obstructed in the water, and this affects the growth of aquatic vegetation. All the chemicals that are drained into the water have harmful effects on every organism that lives there. The effect of water pollution on marine animals and plants is visible in two phenomena in particular — eutrophication and biomagnification.
The Process Of Eutrophication
Eutrophication is the process of depletion of oxygen from waterbodies, occurring either naturally or due to human activities. Fish and other water organisms breathe the oxygen dissolved in the water itself, so a water body losing its oxygen is a water body slowly becoming uninhabitable.
The process takes place due to the introduction of nutrients and chemicals into the water. These arrive through the discharge of domestic sewage, through industrial effluents, which is the waste liquid a factory releases, and through fertilisers washed off agricultural fields. The consequent nutrient accumulation results in a phenomenal growth of phytoplankton and algae — the tiny floating plants of the water surface — which spread into a thick layer.
That layer is what does the damage. It reduces the penetration of oxygen, light and heat into the water body below. As a result, most of the organisms die, draining the water of all its oxygen.
Flowchart
Fig. 18.A5 Caption: Feeding a lake is what starves it of oxygen. Nodes: domestic sewage, industrial effluents and fertilisers from fields enter the water → nutrients accumulate → phytoplankton and algae grow enormously → the surface layer blocks oxygen, light and heat from reaching the water below → most organisms die → the water is drained of all its oxygen
Diagram
Fig. 18.2 Caption: Eutrophication. Brief: Photograph of a lake surface almost wholly covered by green algal growth, with hills and forest behind — show the thickness and continuity of the surface layer.
Biomagnification And Bioaccumulation
The term biomagnification means increasing the concentration of various toxic substances along the food chain. Toxic substances present at the level of primary producers, which are the green plants at the base of the chain, get concentrated at each trophic level as they move up the food chain. A trophic level is simply one step in that chain — producers, then the animals that eat them, then the animals that eat those. The phenomenon of concentrated toxic deposition at the higher trophic level is known as bioaccumulation.
The reason this happens is that an animal eats many times its own weight over its lifetime, but the toxin does not leave its body. For example, if there are traces of toxic chemicals in water, then their concentration in algae will be much higher. When fish eat the algae, the concentration of toxins will increase further. Therefore, the accumulation of a small amount of toxic chemicals in water can have a serious impact on the fish that live in it.
Diagram
Fig. 18.3 Caption: Biomagnification. Brief: Vertical ladder of four trophic levels with an arrow pointing up the chain at each step — producers (water plants) 0.04 ppm, primary consumers (small fish) 0.23 ppm, secondary consumers (large predatory fish) 2.07 ppm, tertiary consumers (fish-eating bird of prey) 13.8 ppm; print the note that these are representative values of the concentration of DDT and its derivatives in the tissues, in parts per million.
The Elm Trees Of Illinois
An example of the phenomenon of biomagnification was first noticed in Illinois, in the United States, where elm trees were sprayed with DDT, a pesticide. A large number of birds like robins died near these trees.
It was later discovered that these birds perished due to DDT poisoning. The lethal dose came from the earthworms which they consumed, and the earthworms had concentrated the DDT residue by feeding on the fallen elm leaves. The birds had never been sprayed. The poison reached them along the food chain, three steps from where it was put down.
The last figure is the one to hold on to. The tertiary consumer carries 345 times the concentration the producers carried, and it did nothing different from any other animal — it simply ate at the top of the chain. This is why a level of pollution that looks harmlessly small in a water sample is not harmless at all, and why the animals that suffer first are usually the ones furthest from the pollution.
Other Effects On Water Bodies
The other effects of water pollution are as follows. (a) Phosphorus and nitrates from fertilisers and detergents contaminate surface water, where they act as nutrients and promote the growth of oxygen consuming algae. This in turn reduces the amount of dissolved oxygen in the water and kills fish and other aquatic organisms. (b) Industrial effluents result in the addition of poisonous chemicals such as arsenic, mercury, cadmium and lead, which kill aquatic organisms. These chemicals may reach the human body through contaminated food such as fishes. (c) Hot waste water released from power stations increases the temperature of water resources, reduces the oxygen level in them, and makes them incapable of supporting life. (d) Sea water polluted with crude oil leakage causes oil spills, which contaminate the sea water and lead to the death of marine organisms.
18.4.2 Effects On Human Health
Water reaches human beings by two routes — as drinking water, and as food that lived in the water. Both routes carry pollution, and they carry different kinds of it.
Pathogens In Drinking Water
Most of the waste waters, especially sewage, contain pathogens, which are disease causing organisms like bacteria, viruses and protozoa. These pathogens enter the human body from contaminated drinking water.
They are responsible for several water-borne diseases, and the chapter names seven of them: cholera, typhoid, diarrhoea, dysentery, hepatitis, polio and jaundice. What these have in common is not the organism but the route — every one of them travels from waste to water to a person drinking it.
Toxic Compounds In Water
Pollutants such as heavy metals, pesticides, cyanides and many other organic and inorganic compounds are harmful to all organisms. Some of these toxic substances do not undergo biodegradation, which means they are not broken down by living organisms in the soil and water, and so they remain in the environment for a long time.
Toxic substances polluting the water ultimately affect human health. Some heavy metals like lead, mercury and cadmium cause various types of diseases. (a) Mercury dumped into water is transformed into water soluble methyl mercury by bacterial action, and methyl mercury accumulates in fish. People in Japan suffered from a disease called Minamata, which resulted in numbness of body parts, vision and hearing problems and abnormal mental behaviour. It was caused by the consumption of methyl mercury contaminated fish caught from Minamata Bay in Japan. (b) Pollution by the heavy metal cadmium caused the disease called Itai-itai among the people in Japan. (c) Water contaminated with arsenic causes mental disorders, liver damage, known as cirrhosis, lung cancer, ulcers in the gastrointestinal tract, and kidney failure. (d) Fluoride containing pollutants cause a disease called fluorosis, which causes discolouring of dental enamel and black and brown stains on the teeth. It also causes respiratory and gastrointestinal problems.
The first of these deserves a second look, because it is biomagnification arriving at a human being. Nobody in Minamata drank mercury. The mercury was dumped in water, changed form, gathered in fish, and reached people at the end of a chain they could not see when they sat down to a meal.
18.5 Effects Of Soil Pollution
Soil pollution affects human beings and animals indirectly, through food chains. Nobody eats soil. What people eat is what grew in the soil, or what grazed on what grew in the soil, and that is the route by which a polluted field reaches a plate. The effects of soil pollution on the environment, on human health and on other organisms are discussed below.
Flowchart
Fig. 18.A6 Caption: A pollutant in the soil reaches people by four separate routes. Nodes: pollutant enters the soil → taken up by crops → eaten by human beings / taken up by fodder plants → eaten by grazing animals → livestock → human beings / percolates downward → groundwater → drinking water / carried off by agricultural run-off → nearby water bodies → eutrophication
18.5.1 Effects On Environment
The soil does not hold a pollutant still. Water moving down through it and water running off it both carry the pollutant somewhere else, which is why the effects listed here are found in the plants above the soil and in the water below it. (a) Nitrogenous fertilisers produce a toxic concentration of nitrate and nitrite in the leaves of the plants growing in that soil. (b) Industrial and chemical wastes cause pollution of underground water, the water held in the spaces and cracks of the rock beneath the surface. (c) Nitrogen and phosphorous from the fertilisers accumulate in nearby water bodies along with agricultural run-off and cause eutrophication. Chemicals may also percolate, meaning seep slowly downward through the soil, and contaminate groundwater resources. (d) Land and soil pollution is responsible for the loss of fertility and productivity of soil, so the same field yields less than it once did.
18.5.2 Effects On Human Health
The harm reaches human health mostly through what is grown and eaten. (a) Soil contains many pathogenic bacteria, viruses and intestinal worms, which are transmitted to human beings by the consumption of fruits and vegetables. These pathogens cause various types of diseases. (b) Radioactive fallout on vegetation is the source of radioisotopes, which enter the food chain through the grazing animals. Fallout is the radioactive material that settles out of the air onto the ground, and a radioisotope is a form of an element that gives off radiation. Some of these radioisotopes cause abnormalities. (c) The use of human and animal excreta as manure pollutes the soil. Excreta contains pathogens that contaminate the soil and vegetable crops, and so affect the health of human beings.
Washing a vegetable deals with what is on its surface. It does not deal with what the plant has taken up through its roots, and that is the difference between soil pollution and dirt.
18.5.3 Effects On Other Organisms
Soil is not merely a material. It is full of micro-organisms — living things far too small to see — and it is their work that keeps the soil fertile. Pollution reaches them first. (a) Particles in the sewage may clog the small pores of the soil and destroy the micro-organisms there, which are the organisms responsible for soil enrichment. (b) Radioactive material enters the food chain from the soil through the crops cultivated, and passes to livestock and human beings. (c) Many pesticides are absorbed by plants and reach animals and human beings via food chains.
18.6 Effects Of Radioactive Pollution
Radioactive pollution is different from the other four in one important way. There is nothing to see, nothing to smell and nothing to taste, because what is released is radiation — energy given off by certain unstable substances — rather than a gas, a liquid or a dust.
Radioactive pollution is caused by several activities, and the chapter names four of them. (a) The testing of nuclear weapons. (b) The establishment of nuclear power plants. (c) The mining and refining of radioactive substances like uranium, thorium and plutonium. (d) Medical treatment using X-rays.
18.6.1 Effects On Environment
Radiations emitted from radioactive materials, and the disposal of radioactive wastes, cause pollution and damage the environment. Disposal is part of the problem rather than the end of it, because the high level products of nuclear wastes remain in the environment for several hundred years.
Other radioactive threats to the environment are the accidents connected with the activities of nuclear reactors, nuclear-powered vessels and satellites. These are threats of a particular kind: they are unlikely, but when one occurs it releases a large quantity of radioactive material at a single place in a very short time.
18.6.2 Effects On Human Health
Radiations affect living organisms. They cause harmful changes in the body cells, and also at the genetic level, which means in the instructions a cell passes on when it divides. The chapter separates the two kinds of damage, and the difference between them is worth holding clearly. (a) Genetic variation. The damage caused by radiations is often seen in the offspring, and may be transmitted to many generations. (b) Somatic variation. Short term exposures to radiation can cause damage to organs of the body. The harm done includes breast cancer, thyroid cancer, lung cancer and brain cancer, sterility, which is the inability to have children, and defective eyesight.
The two are told apart by who carries the damage. Somatic variation stays in the body that was exposed, and shows up as illness in that person’s own organs. Genetic variation is carried in what that person passes on, so it appears in children and grandchildren who were never exposed to anything. What they share is the cause: in both, radiation has altered cells that would otherwise have worked normally.
Flowchart
Fig. 18.A7 Caption: Radiation reaches the body directly, and reaches it again through the food chain. Nodes: radioactive substance released → radiation reaches the body directly / substance penetrates the soil → enters the food chain → concentrates in the body tissue of animals → reaches human beings as food → damage to cells → somatic variation: cancers, sterility, defective eyesight in the person exposed / genetic variation: damage in the offspring, passed on for many generations
18.6.3 Effects On Animals
Radioactive substances resulting from the explosion of nuclear devices, or from nuclear wastes, penetrate the soil. From the soil they enter into the food chain, get concentrated in the body tissue of animals, and have adverse effects on them. This is the same climb up the food chain seen earlier with toxic chemicals, working now with radioactive material.
The Chernobyl accident is considered the most disastrous nuclear power plant accident, both in terms of cost and casualties. What the case shows, though, is not only its scale. The people, the pine forest and the animals were harmed by the same release at the same time, which is what makes radioactive pollution so hard to contain: it does not act on one target and spare the rest. And because high level nuclear waste stays radioactive for several hundred years, the area’s problem long outlasts the day the reactor exploded.
Diagram
Fig. 18.4 Caption: Chernobyl disaster. Brief: Aerial photograph of the wrecked reactor building at Chernobyl — show the collapsed roof, scattered debris and the intact chimney stack alongside; no people in frame.
18.7 Summary
- All types of pollution — noise, air, water, soil and radioactive — have an impact on all living organisms and on their environment, and the pollutants released are responsible for environmental degradation.
- The effects on human beings cover a wide range.
- At the mild end there is discomfort, felt at once and recovered from.
- At the severe end there are long term effects such as cancer and physical deformities.
- Increased pollution also causes psychological and behavioural disorders.
- Noise pollution damages the environment because sound is a vibration that shakes whatever it reaches.
- Noise booms cause cracks in national and archaeological monuments.
- Very high levels of noise cause cracks in hills.
- High intensity explosions break glass panes and cause vibrations in buildings.
- Noise affects human health in five ways: loss of hearing, interference with communication, interference with sleep, mental or physiological effects, and effects on physical health with psychological problems.
- Continuous exposure above 100 dB harms hearing within a fairly short time, and continuous levels above about 100 dB may damage the inner ear.
- Below about 90 dB, noise has little physical effect on biological performance.
- Noise in industries interferes with efficiency and communication and raises the possibility of accidents.
- Table 18.1 records what has been observed at particular sound levels, from the threshold of audibility below 90 dB to permanent damage to hearing at 190 dB.
- Noise also affects animals: birds avoid migrating to places where the noise level is above 100 dB, supersonic aircraft and railway noise may cause miscarriage in mammals and fishes, and some birds have stopped laying eggs.
- Air pollution is the presence in the air of noxious gases and particulates, in harmful concentrations and of such duration and characteristics as to injure plants, animals, human beings and materials.
- Carbon dioxide and other greenhouse gases trap the earth’s heat and cause global warming, which has six stated effects on the environment.
- The Northern hemisphere heats more than other regions, and snowlines in temperate mountains melt earlier.
- Winter and night temperatures rise more than summer and day temperatures.
- Evaporation of surface water increases and warmer air holds more moisture, affecting water resources, forests, agriculture, power generation, infrastructure, tourism and health.
- Eroded soil without vegetative cover cannot retain moisture, and droughts follow.
- Melting glaciers form lakes behind mounds of debris, which fill faster than they drain and flood more frequently.
- Deltas, including the delta area of the Ganga, Brahmaputra and Indus, are threatened by flooding, erosion and salt intrusion, and the loss of coastal mangroves affects fisheries.
- How badly air pollution harms a person depends on the duration of exposure and the concentration of the pollutants, and Table 18.2 sets out what eight common pollutants do to the body.
- Short-term effects include irritation of the eyes, nose and throat, respiratory infections, headaches and nausea, and slurring of speech.
- Long-term effects include chronic respiratory disease, lung cancer, cardiovascular diseases and coma, and damage to the nerves, brain, liver and kidneys.
- The Bhopal Gas Tragedy of December 3, 1984 shows an extreme concentration acting over a very short duration, killing 3500 people and affecting about 40,000 across 100 sq km.
- Air pollution also acts on plants, animals and materials.
- SO₂, NO₂, ozone and PAN destroy chlorophyll, disrupt photosynthesis, cause premature leaf fall and reduce crop yields.
- Animals feeding on plants coated with particulate matter suffer arsenic poisoning, and lead poisoning causes bronchitis and loss of appetite in pets.
- Sulphuric acid mist and acid rain damage marble and limestone, corrode steel, copper and zinc, embrittle paper, disintegrate leather and weaken textiles.
- Water pollution obstructs photosynthesis in the water and shows itself in two phenomena.
- Eutrophication is the depletion of oxygen from waterbodies: nutrients from sewage, effluents and fertilisers make algae and phytoplankton grow so thickly that oxygen, light and heat cannot penetrate, and the organisms below die.
- Biomagnification is the increasing concentration of toxic substances along the food chain, and the concentrated deposition at a higher trophic level is bioaccumulation, as with the DDT that killed robins in Illinois.
- Water pollution reaches human health by two routes: pathogens in drinking water causing cholera, typhoid, diarrhoea, dysentery, hepatitis, polio and jaundice, and toxic compounds causing Minamata, Itai-itai, arsenic poisoning and fluorosis.
- Soil pollution affects human beings and animals indirectly, through food chains, and also damages the soil itself.
- Fertilisers raise nitrate and nitrite in leaves, run off into water bodies to cause eutrophication, and percolate into groundwater.
- Pathogens in soil reach people through fruits and vegetables, and radioisotopes reach them through grazing animals.
- Sewage particles clog soil pores and destroy the micro-organisms responsible for soil enrichment, and land and soil pollution cause loss of fertility and productivity.
- Radioactive pollution comes from nuclear weapons testing, nuclear power plants, the mining and refining of uranium, thorium and plutonium, and medical X-rays.
- High level nuclear wastes remain in the environment for several hundred years.
- Somatic variation damages the organs of the person exposed, while genetic variation appears in the offspring and may pass through many generations.
- The Chernobyl accident of April 26, 1986 killed 31 of the 237 people who suffered acute radiation sickness, killed four square kilometres of pine forest, and left animals in the worst-hit areas dead or unable to reproduce.
Flowchart
Fig. 18.A8 Caption: Five kinds of pollution, and what each of them damages. Nodes: pollution → noise → environment: cracked monuments, cracked hills, broken glass; human health: deafness, disturbed communication and sleep, tension and illness; animals: migration and breeding disturbed / air → environment: greenhouse gases trap heat → global warming → snowlines, droughts, glacier lakes, deltas; human health: short-term irritation and long-term disease; plants, animals and materials / water → eutrophication and biomagnification kill aquatic life; human health: water-borne diseases and toxic metals / soil → acts indirectly through food chains → crops, livestock, groundwater, loss of fertility / radioactive → environment for several hundred years; human health: somatic and genetic variation; animals through the food chain
What This Chapter Cannot Tell You
The chapter names effects, but it rarely gives amounts. Table 18.1 gives sound levels without saying how long a person stood in them, Table 18.2 names pollutants without giving a concentration, and the figures in Fig. 18.3 are described as representative values rather than measurements from one particular place.
Nor can it tell you how polluted any given town, river or field actually is, because it describes what pollution does rather than where it is worst. The six effects of global warming are set out as expectations about the future, and the chapter offers no measurement of how far each has already gone.
18.8 Check Your Concepts
Look at Table 18.1.
- State the effect observed at 150 dB.
- Explain why this table alone cannot tell you whether a particular worker exposed at that level will suffer permanent damage to hearing.
Using the values printed in Fig. 18.3, calculate how many times greater the DDT concentration in the tertiary consumers is than the concentration in the producers. Show your working, and state the unit the figures are given in.
Arrange the stages of eutrophication in order, beginning with fertiliser washed off a field and ending with the death of the organisms in the water. Then explain why growth at the surface of a water body reduces the oxygen far below it.
The chapter states that the harm done by air pollution depends on the duration of exposure and the concentration of the pollutants. Using these two ideas, explain why the leak at Bhopal caused in a single night the kind of damage that ordinary air pollution usually takes years to cause.
A landfill was reclaimed and sturdy plants were grown on it instead of crops or fruit trees. Why?
Why are nuclear radiations more dangerous than other forms of pollution?
Crude oil from a refinery has leaked into the Kosasthalaiyar river north of Chennai, into the biodiverse Ennore creek where many migratory birds come, and into the Bay of Bengal. List what could have been affected by this pollution, and how.
State briefly how noise pollution is detrimental to human health.
How does air pollution affect the environment?
With the help of a well labelled diagram, explain how the accumulation of toxic substances increases as we move up the food chain.