8 pollution of air and water


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8 pollution of air and water

  1. 1. POLLUTION OF AIR AND WATERP aheli and Boojho were very excited You already know that air consists to hear the news that Taj of a mixture of gases. By volume, about Mahal in Agra is now one of the 78% of this mixture is nitrogen andseven wonders of the world. But they about 21% is oxygen. Carbon dioxide,were disappointed to hear that the argon, methane, ozone and waterbeauty of this monument in white vapour are also present in very smallmarble is being threatened by air quantities.pollution in the area surrounding theTaj. They were eager to know if Activity 18.1something can be done to fight the air You may have covered your noseand water pollution. while passing a brick kiln emitting We are all aware that our smoke or started coughing whileenvironment is not what it used to be. walking on a busy road (Fig. 18.1).Our elders talk about the blue sky, clean On the basis of your experience,water and fresh air that was available compare the quality of air at thein their times. Now the media regularly places given below:reports on the falling quality of the A park and a busy road.environment. We ourselves feel theimpact of the falling quality of air and A residential area and anwater in our lives. The number of people industrial area.suffering from diseases of the respiratory A busy traffic intersection atsystem, for example, is steadily rising. different times of the day e.g. early morning, afternoon and We dread to imagine a time whenclean air and water may no longer be evening.available! You have learnt about the A village and a town.importance of air and water in yourprevious classes. In this chapter, we willstudy about the harmful changes takingplace in our surroundings and theireffects on our lives.18.1 Air PollutionWe can survive for some time without food,but we cannot survive even for a fewminutes without air. This simple fact tells Fig. 18.1 : A congested road in a cityus how important clean air is to us.
  2. 2. One of your observations in the Activity 18.2above activity could be the differences You might have read in thein the amount of smoke in the newspapers that respiratoryatmosphere. Do you know where the problems amongst childrensmoke could have come from? Addition are rising day by day. Conduct aof such substances to the atmosphere survey of households in yourmodifies it. When air is contaminated neighbourhood and among friendsby unwanted substances which have to find out how many children area harmful effect on both the living and suffering from respiratory problems.the non-living, it is referred to as airpollution. Many respiratory problems are caused by air pollution. Let us now try18.2 How does Air Get Polluted? to find out the substances or pollutants which are present in the polluted air.The substances which contaminate the Have you noticed how rapidly theair are called air pollutants. Sometimes, number of vehicles is increasing in oursuch substances may come from natural cities?sources like smoke and dust arising from Vehicles produce high levels offorest fires or volcanic eruptions. pollutants like carbon monoxide, carbonPollutants are also added to the dioxide, nitrogen oxides and smoke (Fig.atmosphere by human activities. The 18.3). Carbon monoxide is producedsources of air pollutants are factories from incomplete burning of fuels such(Fig. 18.2), power plants, automobile as petrol and diesel. It is a poisonousexhausts and burning of firewood and gas. It reduces the oxygen-carryingdung cakes. capacity of the blood. Fig. 18.3 : Air pollution due to automobiles Do you know? If the vehicles registered in Delhi are lined up one after the other, the total length would be nearly equal to the combined lengths of the two longest Fig. 18.2 : Smoke from a factory rivers in the world, Nile and Amazon!242 SCIENCE
  3. 3. Boojho remembers seeing a thick Activity 18.3fog-like layer in the atmosphere,especially during winters. This is smog Prepare a table using the pollutantswhich is made up of smoke and fog. mentioned above. You may even addSmoke may contain oxides of nitrogen more data to the following Table.which combine with other air pollutants Table 18.1and fog to form smog. The smog causes Air Pollutants Sources Effectsbreathing difficulties such as asthma,cough and wheezing in children. Many industries are also responsiblefor causing air pollution. Petroleumrefineries are a major source of gaseous 18.3 Case Study : The Tajpollutants like sulphur dioxide and Mahalnitrogen dioxide. Sulphur dioxide is Over the past 2 decades, India’s mostproduced by combustion of fuels like famous tourist attraction, Taj Mahalcoal in power plants. It can cause located in Agra (Fig. 18.4), has becomerespiratory problems, including a matter of concern. Experts havepermanent lung damage. You have warned that pollutants in air arealready studied about the burning of discolouring its white marble. So, it isfossil fuels in Chapter 5. not only living organisms that get Other kinds of pollutants are affected by polluted air but non-livingchlorofluorocarbons (CFCs) which are things like buildings, monuments andused in refrigerators, air conditioners statues also get affected.and aerosol sprays. CFCs damage the The industries located in and aroundozone layer of the atmosphere. Recall Agra like rubber processing, automobile,that the ozone layer protects us from chemicals and especially the Mathura oilharmful ultraviolet rays of the sun. Have refinery, have been responsible foryou heard of the ozone hole? Try to find producing pollutants like sulphurout about it. Thankfully, less harmful dioxide and nitrogen dioxide. Thesechemicals are now being used in place gases react with the water vapour presentof CFCs. in the atmosphere to form sulphuric acid In addition to the above mentioned and nitric acid. The acids drop down withgases, automobiles which burn diesel rain, making the rain acidic. This isand petrol, also produce tiny particles called acid rain. Acid rain corrodes thewhich remain suspended in air for long marble of the monument. Theperiods (Fig. 18.3). They reduce phenomenon is also called “Marblevisibility. When inhaled, they cause cancer”. Suspended particulate matter,diseases. Such particles are also such as the soot particles emitted byproduced during industrial processes Mathura oil refinery, has contributedlike steel making and mining. Power towards yellowing of the marble.plants give out tiny ash particles which The Supreme Court has takenalso pollute the atmosphere. several steps to save the Taj. It hasPOLLUTION OF AIR AND WATER 243
  4. 4. Fig. 18.4 : Taj Mahalordered the industries to switch to and a part is reflected back into space.cleaner fuels like CNG (Compressed A part of the reflected radiation isNatural Gas) and LPG (Liquefied trapped by the atmosphere. The trappedPetroleum Gas). Moreover, the radiations further warm the earth. If youautomobiles should switch over to have seen a greenhouse in a nursery orunleaded petrol in the Taj zone. elsewhere, recall that the sun’s heat is Discuss with your elders and see allowed to get in but is not allowed towhat they have to say about the go out. The trapped heat warms thecondition of the Taj, 20 or 30 years ago! green house. The trapping of radiationsTry to procure a picture of the Taj Mahal by the earth’s atmosphere is similar.for your scrap book. That is why it is called the greenhouse effect. Without this process, life would not have been possible on the earth. But now it threatens life. CO2 is one of the I am reminded of the gases responsible for this effect. chapter on crops. I You know that CO 2 is one of the wonder whether acid rain components of air. You have also studied affects the soil and plants also.18.4 Greenhouse Effect But how does CO2 contentYou know that the sun’s rays warm the rise in the atmosphere andearth’s surface. A part of the radiation become excessive?that falls on the earth is absorbed by it244 SCIENCE
  5. 5. the role of carbon dioxide in plants. But towards this effect. Like CO2, they areif there is excess of CO2 in the air, it also called greenhouse gases.acts as a pollutant. Global warming has become a major Can you help Paheli find out the concern for governments worldwide.answer to her question? Many countries have reached an On the one hand, CO2 is continuously agreement to reduce the emission ofbeing released because of human greenhouse gases. The Kyoto Protocolactivities. On the other hand, area under is one such agreement.forests is decreasing. Plants utilise CO2 Boojho is surprised to hear that anfrom the atmosphere for photosynthesis, increase in the earth’s temperature bythereby decreasing the amount of CO2 even as little as 0.5 ºC can have such ain the air. Deforestation leads to an serious effect! Paheli tells him that sheincrease in the amount of CO2 in the air had read in the newspapers recently thatbecause the number of trees which the Gangotri glacier in the Himalayasconsume CO 2 is reduced. Human has started melting because of globalactivities, thus, contribute to the warming.accumulation of CO2 in the atmosphere.CO2 traps heat and does not allow it to 18.5 What can be Done?escape into space. As a result, the average What can we do to reduce airtemperature of the earth’s atmosphere pollution?is gradually increasing. This is called There are many success stories in ourglobal warming. fight against air pollution. For example, Other gases like methane, nitrous a few years ago, Delhi was one of theoxide and water vapour also contribute most polluted cities in the world. It was being choked by fumes released from Global Warming automobiles running on diesel and A Serious Threat! petrol. A decision was taken to switch Global warming can cause sea levels to fuels like CNG (Fig. 18.5) and to rise dramatically. In many places, coastal areas have already been flooded. Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. Majority of people living in regions which are threatened by global warming are in Asia. A recent climate change report gives us only a limited time to keep the greenhouse gases at the present level. Otherwise, the temperature may rise by more than 2 degrees Celsius by the end of the century, a level considered dangerous. Fig. 18.5 : A public transport bus powered by CNGPOLLUTION OF AIR AND WATER 245
  6. 6. unleaded petrol. These measures have fuels for our energy requirements. Theseresulted in cleaner air for the city. You could be solar energy, hydropower andmight know of some other examples wind energy.from your area regarding reduction ofair pollution. Share these with your Activity 18.4friends. You have various options of commuting to your school such as Do you know about the “Say no to walking, going by bicycle, travelling crackers” campaign which was by bus or other public transport, organised by children from many schools? This made a big difference using a car individually, travelling to the air pollution levels around by car pool. Discuss in your class Diwali. the impact of each of these options on the quality of air. The quality of air at various locationsis monitored regularly by government Small contributions on our part canand other agencies. We can use this data make a huge difference in the state ofto generate awareness about air the environment. We can plant trees andpollution among friends and nurture the ones already present in theneighbours. neighbourhood. Do you know about Van There is a need to switch over to Mahotsav, when lakhs of trees arealternative fuels instead of the fossil planted in July every year (Fig. 18.6)? Fig. 18.6 : Children planting saplings246 SCIENCE
  7. 7. Boojho and Paheli once happened to Activity 18.5go to an area where some people wereburning dry leaves. They started Try to collect samples of water fromcoughing because the entire area was full a tap, pond, river, well and lake. Pour each into separate glassof smoke. Paheli thought it would be a containers. Compare these forbetter option to put them in a compost smell, acidity and colour. Completepit rather than burning. What do you the following Table.think? Table 18.218.6 Water Pollution Smell Acidity ColourIn Class VII you learnt that water is a Tap Waterprecious resource. Think and list the Pond Watervarious activities in which we needwater. We saw that water is becoming River Waterscarce due to increase in population, Well Waterindustries and agricultural activities.You have also studied how water Lake Waterbecomes “dirty” after we use it forwashing clothes, bathing, etc. This 18.7 How does Water Getmeans that we are adding somematerials to the water, which spoil its Polluted?quality and change its smell and colour. Case Study Whenever harmful substances such Ganga is one of the most famous riversas sewage, toxic chemicals, silt, etc., get of India (Fig. 18.7). It sustains most ofmixed with water, the water becomes the northern, central and easternpolluted. The substances that pollute Indian population. Millions of peoplewater are called water pollutants. depend on it for their daily needs and Fig. 18.7 : Course of the river GangaPOLLUTION OF AIR AND WATER 247
  8. 8. livelihood. However, recently a study by and defecating in the river. They alsothe World Wide Fund for Nature (WWF) throw garbage, flowers, idols of godsfound that Ganga is one of the ten most and goddesses and non-biodegradableendangered rivers in the world. The polythene bags into the river.pollution levels have been rising for At Kanpur the amount of water ismany years. We have reached this stage comparatively small and the flow of thebecause the towns and cities, through river is very slow. In addition, Kanpurwhich the river flows, throw large has more than 5000 industries. Thesequantities of garbage, untreated sewage, include fertiliser, detergent, leather anddead bodies, and many other harmful paint industries. These industrial unitsthings, directly into the river. In fact the discharge toxic chemical wastes into theriver is “dead” at many places where river.the pollution levels are so high that Based on the above informationaquatic life cannot survive. think of the answers to the following An ambitious plan to save the river, questions :called the Ganga Action Plan was What are the factors responsible forlaunched in 1985. It aimed to reduce pollution of the river ?the pollution levels in the river. However, What steps can be taken to restorethe increasing population and the river Ganga to its past glory ?industrialisation have already damaged How would the disposal of garbage,this mighty river beyond repair. etc., affect the living organisms in the Let us take a specific example to river ?understand the situation. The Gangaat Kanpur in Uttar Pradesh (U.P.), has Many industries discharge harmfulone of the most polluted stretches of chemicals into rivers and streams,the river (Fig. 18.8). Kanpur is one of causing the pollution of waterthe most populated towns in U.P. People (Fig. 18.9). Examples are oil refineries,can be seen bathing, washing clothes paper factories, textile and sugar millsFig. 18.8 : A polluted stretch of the river Fig. 18.9 : Industrial waste discharged into a Ganga river248 SCIENCE
  9. 9. and chemical factories. These industries food wastes, detergents, microor -cause chemical contamination of water. ganisms, etc. Can ground water getThe chemicals released include arsenic, polluted by sewage? How? Waterlead and fluorides which lead to toxicity contaminated with sewage may containin plants and animals. There are bacteria, viruses, fungi and parasitesregulations to prevent this. Industries which cause diseases like cholera,are supposed to treat the waste typhoid and jaundice.produced before discharging it into The bacteria present in the faeceswaters, but quite often the rules are not of mammals are indicators of thefollowed. The soil is also affected by quality of water. If water has theseimpure water, causing changes in bacteria, it means that it has beenacidity, growth of worms, etc. contaminated by fecal matter. If such We have learnt in Chapter 1 the water is used by us, it can cause variousimportance of pesticides and weedicides infections.for the protection of crops. However, allthese chemicals dissolve in water and Do you know?are washed into water bodies from the Hot water can also be a pollutant !fields. They also seep into the ground This is usually water from powerto pollute ground water. plants and industries. It is released Have you seen ponds which look into the rivers. It raises thegreen from a distance because they have temperature of the waterbody,a lot of algae growing in them? This is adversely affecting the animals andcaused by excessive quantities of plants living in it.chemicals which get washed from thefields. These act as nutrients for algae 18.8 What is Potable Waterto flourish. Once these algae die, they and How is Waterserve as food for decomposers like Purified ?bacteria. A lot of oxygen in the waterbody gets used up. This results in adecrease in the oxygen level which may Activity 18.7kill aquatic organisms. Let us construct a water filter with simple, everyday materials.Recall Activity 18.6 Take a plastic bottle and cut it You had investigated the sewage into 2 halves at the centre. Use the disposal system of your locality in upper half as a funnel by putting it Class VII. upside down in the lower half. Make Do you remember how the layers in it with paper napkin or a sewage was collected from your fine cloth followed by, cotton, sand home and where it went thereafter. and then gravel. Now pour dirty water through the filter and observe Sometimes untreated sewage isthrown directly into rivers. It contains the filtered water.POLLUTION OF AIR AND WATER 249
  10. 10. water. Boiling kills the germs present Discuss the following questions in the water. amongst yourselves and with your Chlorination is a commonly used teacher: chemical method for purifying water. Why do we need to filter water It is done by adding chlorine tablets before drinking ? or bleaching powder to the water. We Where do you get your drinking must be cautious. We should not water from? use more chlorine tablets than What will happen if we drink specified. polluted water? 18.9 What can be Done? Boojho is very upset. He tells Pahelithat he drank water which looked clear Activity 18.8and was without any smell, but still he Investigate the level of awarenessfell sick ! about water pollution in your area. Paheli explains that water which Collect data on the sources oflooks clean may still have disease- drinking water and the methods ofcarrying microorganisms and dissolved sewage disposal.impurities. So, it is essential to purify What are the common water-bornewater before drinking, for example, by diseases in the community? You canboiling. consult your local doctor/health Water which is suitable for drinking worker for this.is called potable water. You have seen Which are the governmental andhow various physical and chemical non-governmental organisationsprocesses in the sewage treatment working in this field? What are theplants help to clean water before measures being taken by them fordischarging it into water bodies. generating awareness?Similarly, municipal bodies treat thewater before supplying it to households. Laws for industrial units should be Do you know? strictly implemented so that polluted water is not disposed off directly into 25% of the world’s population is without safe drinking water ! rivers and lakes. Water treatment plants should be installed in all industrial Let us see how water can be made areas (Fig. 18.10). At our individualsafe for drinking: levels we should consciously save water You have already seen how water is and not waste it. Reduce, reuse and filtered. This is a physical method of recycle should be our mantra ! removing impurities. A popular Think of your daily routine – How household filter is a candle type can you save water? filter. We can think of creative ideas like Many households use boiling as a reusing water used for washing and for method for obtaining safe drinking other household tasks. For example,250 SCIENCE
  11. 11. Fig. 18.10 : Water treatment plantwater used for washing vegetables may of our daily lives. Unless we all realisebe used to water plants in the garden. our responsibility and start using Pollution is no longer a distant environment-friendly processes, the veryphenomenon. It is affecting the quality survival of our planet is in danger. Do you know? While brushing your teeth, leaving the tap running may waste several litres of water. A tap that drips once every second wastes a few thousand litres of water every year. Think about it !POLLUTION OF AIR AND WATER 251
  12. 12. KEYWORDS WHAT YOU HAVE LEARNT ACID RAIN Air pollution is the contamination of air by impurities which may have a harmful impact AIR POLLUTION on the living organisms and the non-living CHEMICAL components. CONTAMINATION Pollutants are the substances which contaminate air and water. GLOBAL WARMING Carbon monoxide, nitrogen oxides, carbon GREENHOUSE dioxide, methane and sulphur dioxide are the EFFECT major pollutants of air. Increasing levels of greenhouse gases like CO2 POLLUTANTS are leading to global warming. POTABLE WATER Water pollution is the contamination of water by substances harmful to life. WATER POLLUTION Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water. Water which is purified and fit for drinking is known as potable water. Water is a precious natural resource. We must learn to conserve it. Exercises 1. What are the different ways in which water gets contaminated ? 2. At an individual level, how can you help reduce air pollution? 3. Clear, transparent water is always fit for drinking. Comment. 4. You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents. 5. Explain the differences between pure air and polluted air. 6. Explain circumstances leading to acid rain. How does acid rain affect us? 7. Which of the following is not a greenhouse gas? (a) Carbon dioxide (b) Sulphur dioxide252 SCIENCE
  13. 13. (c) Methane EXERCISES (d Nitrogen 8. Describe the ‘Green House Effect’ in your own words. 9. Prepare a brief speech on global warming that you have to make in your class. 10. Describe the threat to the beauty of the Taj Mahal. 11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms? Extended Learning — Activities and Projects 1. In some cities, a pollution check has been made compulsory for vehicles. Visit a petrol pump in order to learn about the process of conducting a pollution check. You may systematically record your findings in the following areas: Average number of vehicles checked per month. Time taken to check each vehicle. Pollutants checked for. The process of testing. Permissible levels of emission of various gases. Measures taken if the emitted gases are above the permissible limits. How frequently is a pollution check required ? 2. Conduct a survey in your school to investigate various environment related activities that have been undertaken. The class can divide itself into two groups, with each group looking at a different area. For example, one group can find out whether there is an environment club in the school. What are its objectives ? What is its calendar of events ? How can you become a member ? If your school does not have such a club, you can even think of starting one along with a few of your friends. 3. Organise a field visit to a river in or around your town with the help of your teachers.POLLUTION OF AIR AND WATER 253
  14. 14. Observations followed by discussion could focus on : The history of the river. Cultural traditions. Role of the river in meeting the town’s water needs. Pollution concerns. Sources of pollution. Effects of pollution on the people living by the riverside as well as those living far away. 4. Find out with the help of your teachers and the internet (if possible), whether there are any international agreements to control global warming. Which are the gases covered under these agreements? www.edugreen.teri.res.in/explore/air/air.htm www.edugreen.teri.res.in/explore/water/pollu.htm www.cpcb.nic.in/citizen’s%Charter/default_citizen’s.html coe.mse.ac.in/kidswater.asp coe.mse.ac.in/kidsair.asp254 SCIENCE