Pollution of Air and Water – Long Answer Type Questions

Pollution is any undesirable change in the physical, chemical or biological characteristics of the environment that adversely affects living organisms. When harmful substances are added to air, water or soil beyond a certain limit, they make them impure and unsafe for life.

In this chapter, you mainly study about two types of pollution:

• Air pollution: It is the contamination of air by harmful gases, smoke and dust. For example, smoke from vehicle exhausts and chimneys of factories releases gases like carbon monoxide and sulphur dioxide into the air.
• Water pollution: It is the contamination of water bodies like rivers, lakes and seas by harmful substances. For example, discharge of untreated sewage and chemical effluents from factories into rivers pollutes water.

Both these types of pollution directly affect the health of humans, animals and plants and disturb the natural balance of the environment.

Pollutants are substances which cause pollution when they are present in the environment in greater than normal amounts. They may be solids, liquids or gases and can be natural or man-made.

Pollutants are of two main types:

• Biodegradable pollutants: These are substances that can be broken down into harmless simpler forms by microorganisms such as bacteria and fungi. Examples include vegetable peels, paper and human/animal waste.
• Non-biodegradable pollutants: These are substances that cannot be easily decomposed by natural organisms and persist in the environment for a very long time. Examples include plastics, glass, metals and synthetic detergents.

Non-biodegradable pollutants are more harmful because they accumulate in the environment, choke drains and water bodies and may enter the food chain. For example, plastic bags thrown in water bodies can kill aquatic animals and remain in the environment for many years.

Human activities are the major cause of both air and water pollution. To fulfil our needs for transport, energy, food and comfort, we carry out actions that release pollutants into the environment.

Some examples are:

• Burning of fuels: We burn coal, petrol, diesel and wood for running vehicles, industries and for cooking. This releases harmful gases like carbon monoxide, carbon dioxide, sulphur dioxide and nitrogen oxides into the air.
• Industrial activities: Factories and power plants emit smoke and dust into the atmosphere and release chemical effluents into rivers and lakes.
• Discharge of sewage: Wastewater from homes, offices and markets is often released directly into water bodies without treatment, causing water pollution.
• Agricultural practices: Excessive use of fertilisers and pesticides on fields is washed into ponds and rivers by rainwater, making the water toxic for aquatic life.

Thus, careless human activities disturb the natural purity of air and water and create serious environmental problems.

The environment maintains a natural balance in which air, water, soil, plants, animals and microorganisms depend on each other. Pollution disrupts this balance.

When air is polluted, plants may not be able to perform photosynthesis properly and their growth is affected. This reduces the food available for herbivores and, in turn, affects carnivores. Harmful gases like sulphur dioxide and nitrogen oxides also cause acid rain which damages forests and crops.

Similarly, water pollution reduces dissolved oxygen in water and kills fish and other aquatic organisms. When these organisms die in large numbers, the food web of aquatic ecosystems breaks down. Polluted water may also spread diseases in humans and animals that depend on these water sources.

In this way, pollution at one place can spread its effect through air, water and food chains, disturbing the balance of entire ecosystems.

Air pollution is the presence of harmful and unwanted substances in the air that make it unfit for humans, animals and plants. These substances are called air pollutants.

In urban areas, the major sources of air pollution are:

• Vehicle emissions: Cars, buses, trucks and two-wheelers burn petrol and diesel and release carbon monoxide, nitrogen oxides and unburnt hydrocarbons.
• Industrial smoke: Factories and power plants emit smoke containing sulphur dioxide, nitrogen oxides and tiny particles of ash and dust.
• Construction activities: Demolition and building works produce a lot of dust and fine particles that remain suspended in the air.
• Burning of garbage and biomass: Burning of dry leaves, garbage and crop residues in and around cities adds smoke and harmful gases to the air.

Because of these sources, the air quality in many cities becomes poor, especially near busy roads and industrial areas.

Carbon monoxide (CO) is a colourless and odourless gas produced by incomplete burning of fuels. It combines with haemoglobin in the blood more strongly than oxygen and forms carboxyhaemoglobin. This reduces the oxygen-carrying capacity of blood and can cause headache, dizziness, unconsciousness and even death in high concentrations.

Sulphur dioxide (SO₂) is produced from burning coal and oil containing sulphur. When inhaled, it irritates the nose, throat and lungs and can trigger asthma and bronchitis. In the atmosphere, it can combine with water vapour to form sulphuric acid, which leads to acid rain.

Nitrogen oxides (NO and NO₂) are mainly released from vehicle exhausts and power plants. These gases cause irritation of eyes and respiratory problems and also participate in the formation of smog and acid rain.

Thus, these gases not only harm human health but also damage plants, buildings and contribute to long-term environmental problems.

Smog is a thick, fog-like, smoky haze formed when smoke and other air pollutants mix with fog near the ground. The word “smog” comes from the words “smoke” and “fog”. It is common in big cities, especially during winter mornings when the air is still and cold.

Smog is formed when pollutants from vehicle exhausts, industries and burning of fuels react in the presence of sunlight and mix with water droplets in fog. This forms a brownish or grey blanket over the city.

The harmful effects of smog include:

• Reduced visibility, which can cause road accidents and delays in transport.
• Irritation in eyes, nose and throat, causing burning sensation and watering of eyes.
• Worsening of respiratory diseases like asthma and bronchitis, especially in children and elderly people.

Therefore, smog is an indicator of high air pollution and is very harmful to health and daily life.

Acid rain is rainwater that has become more acidic than normal due to the presence of dissolved acids like sulphuric acid and nitric acid. These acids are formed from gaseous pollutants in the air.

When fossil fuels are burnt in factories and vehicles, they release sulphur dioxide and nitrogen oxides into the atmosphere. These gases react with oxygen and water vapour to form sulphuric and nitric acids. When clouds containing these acids precipitate, we get acid rain.

Effects of acid rain are:

• On soil: Acid rain reduces soil fertility by damaging soil organisms and dissolving important nutrients. This affects plant growth and crop yield.
• On water bodies: Lakes and rivers become acidic, which is harmful to fish and other aquatic life. Many species may die if the water becomes too acidic.
• On monuments and buildings: Acid rain reacts with marble and limestone and slowly corrodes structures. Famous monuments like the Taj Mahal have been affected by acid rain and industrial pollution.

Thus, acid rain is a serious environmental problem that damages both living and non-living components of the environment.

Global warming is the gradual increase in the average temperature of the Earth’s atmosphere due to the enhanced greenhouse effect caused by human activities.

The main cause of global warming is the increase in the concentration of greenhouse gases like carbon dioxide, methane and nitrous oxide. These gases are released by burning fossil fuels in vehicles and industries, deforestation, use of certain fertilisers and decomposition of waste in landfills.

Harmful effects of global warming include:

• Melting of glaciers and polar ice caps: This leads to a rise in sea level, which can cause flooding of coastal areas and loss of land.
• Change in climate patterns: Some regions may experience more droughts, others may face heavy rainfall and storms. This affects agriculture and water availability.
• Loss of biodiversity: Many plants and animals cannot adapt quickly to the changing temperature and may become endangered or extinct.

Therefore, controlling global warming is essential for the safety of all life on Earth.

Air pollution in cities can be controlled only when both the government and citizens work together.

Measures by the government:

• Setting emission standards for vehicles and making regular pollution-under-control (PUC) checks compulsory.
• Encouraging the use of cleaner fuels like CNG and electricity in public transport.
• Shifting polluting industries away from residential areas and enforcing strict norms on factory emissions.
• Developing efficient public transport systems such as metro rail and buses so that people depend less on private vehicles.

Measures by citizens:

• Using public transport, carpooling, walking or cycling for short distances.
• Keeping vehicles well-maintained to reduce smoke and fuel consumption.
• Avoiding burning of garbage, leaves and firecrackers unnecessarily.
• Planting and protecting trees in neighbourhoods and participating in awareness campaigns.

When rules are properly enforced and people follow eco-friendly habits, air quality in cities can improve significantly.

Compressed Natural Gas (CNG) is called a clean fuel because it burns more completely than petrol or diesel and produces fewer harmful gases and smoke.

Advantages of CNG:

• It produces very little carbon monoxide and unburnt hydrocarbons, so it reduces air pollution.
• It burns efficiently and does not leave much residue in the engine, so engine life increases and maintenance cost decreases.
• CNG is cheaper than petrol and diesel in many cities, making it economical for regular transport.

Limitation: The main limitation is that CNG filling stations may not be available everywhere. Vehicles may have to travel long distances to refill, especially in small towns and villages.

Despite this limitation, using CNG in buses and other vehicles has proved very helpful in improving air quality in many cities.

Trees play a very important role in controlling air pollution. They absorb carbon dioxide and release oxygen during photosynthesis, thus improving the composition of air. Their leaves trap dust, smoke and other suspended particles, reducing the amount of pollutants we inhale.

In addition, trees cool the surroundings, reduce noise and provide shelter to birds and other organisms. Green belts around cities and along roads act as natural barriers against pollution.

A school-level activity to promote tree plantation can be a “Van Mahotsav” celebration. Students, along with teachers, can plant saplings in the school campus and nearby parks. Each student or class can adopt a tree and take responsibility for watering and protecting it. Poster-making competitions and rallies can be organised to spread awareness in the neighbourhood about the importance of trees.

Such activities not only improve the environment but also develop a sense of responsibility among students towards nature.

The Air Quality Index (AQI) is a number and colour code that tells us how clean or polluted the air is in a particular area on a given day. It is calculated by measuring the amount of major air pollutants like particulate matter, sulphur dioxide, nitrogen oxides and ozone in the air.

An AQI chart usually has different colour bands such as good, satisfactory, moderate, poor, very poor and severe. Each band gives information about possible health effects and suggested precautions.

Families can use AQI information in their daily life by:

• Avoiding outdoor exercise and heavy physical work when the AQI is very poor or severe.
• Keeping windows closed and using masks during high pollution days, especially for children, elderly people and those with respiratory problems.
• Planning outdoor activities like games and picnics on days when the AQI is good or satisfactory.

Thus, AQI helps people protect their health and also reminds them of the need to reduce air pollution.

Water pollution is the contamination of water bodies like rivers, lakes, ponds, seas and oceans by harmful substances, making the water unfit for drinking, bathing or supporting aquatic life.

The major causes of water pollution are:

• Discharge of sewage: Wastewater from homes, offices and markets containing soaps, detergents, oils and human excreta is often released into rivers without treatment.
• Industrial effluents: Factories release hot water and liquid waste containing acids, heavy metals and dyes into nearby water bodies.
• Agricultural runoff: Excess fertilisers and pesticides from fields are washed by rain into ponds and rivers, adding harmful chemicals.
• Oil spills and marine activities: Leakage of oil from ships and tankers pollutes seas and oceans.
• Dumping of solid waste: Throwing plastic bags, bottles, religious materials and other garbage into water bodies degrades water quality.

All these activities reduce dissolved oxygen, harm aquatic life and make water unsafe for human use.

Eutrophication is the process by which a water body becomes enriched with nutrients, especially nitrates and phosphates, leading to excessive growth of algae and other aquatic plants.

When fertilisers used in fields and sewage from towns rich in nutrients reach ponds and lakes, algae grow rapidly on the surface, forming a thick green layer called an algal bloom. This bloom blocks sunlight from reaching the deeper layers of water, so underwater plants cannot photosynthesise properly and may die.

After some time, the algae themselves die and start decomposing. Decomposer bacteria use up a large amount of dissolved oxygen present in water during decomposition. As a result, the level of oxygen drops so much that fish and other aquatic animals cannot survive and die due to suffocation.

Thus, eutrophication and algal blooms disturb the entire aquatic ecosystem.

Polluted water may contain harmful microorganisms and toxic chemicals. Drinking such water can cause various diseases and health problems in humans.

Some water-borne diseases are cholera, typhoid, diarrhoea, dysentery and jaundice. These diseases lead to symptoms like vomiting, loose motions, fever and weakness. If not treated in time, they can be life-threatening, especially for small children.

Prevention of such diseases includes the following measures:

• Drinking only safe and purified water by boiling, filtering or using chlorination and water purifiers.
• Using clean and covered containers for storing drinking water.
• Ensuring that sewage and garbage are disposed of properly and not allowed to mix with drinking water sources.
• Creating awareness about personal hygiene, such as washing hands before eating and after using the toilet.

By following these precautions and improving sanitation facilities, many water-borne diseases can be controlled.

Oil spills occur when oil leaks from ships, tankers or offshore drilling into seas and oceans. Oil spreads quickly over the surface of water, forming a thin layer. This layer prevents oxygen from dissolving into water and blocks sunlight. As a result, marine plants and animals do not get enough oxygen and light and many die.

Plastic waste such as bags, bottles, fishing nets and packaging materials thrown into water bodies pose another serious threat. Aquatic animals may swallow plastic pieces, mistaking them for food, which can block their digestive system and cause death. Turtles may get entangled in plastic nets, and birds may be trapped in plastic rings.

Because plastic does not decompose easily, it stays in the environment for a very long time and continuously harms aquatic life. Therefore, careful handling of oil and proper disposal and recycling of plastic are very important to protect water bodies.

Untreated sewage contains a large amount of organic matter such as food particles and human waste, along with disease-causing microorganisms. When this sewage is discharged into a river, microorganisms start decomposing the organic matter.

During decomposition, these microorganisms use up the dissolved oxygen present in the water. As the amount of sewage increases, more oxygen is consumed and its level in water decreases. Fish and other aquatic animals need dissolved oxygen for respiration. If the oxygen level becomes too low, they cannot survive and die.

Besides this, the germs present in sewage can cause diseases in people who use the polluted river water for drinking, bathing or washing. Therefore, it is very dangerous to release untreated sewage into rivers, and it must be properly treated in sewage treatment plants before discharge.

At the community level, people can take several steps to protect nearby ponds, lakes and rivers from pollution.

• Ensuring that sewage from houses is connected to proper drains leading to a treatment facility, not directly to water bodies.
• Providing dustbins and arranging regular collection of solid waste so that people do not throw garbage and plastics into water.
• Organising cleanliness drives to remove waste from the banks and surroundings of water bodies.
• Educating people not to immerse religious materials and idols painted with harmful colours into lakes and rivers.
• Encouraging farmers to use organic manure instead of excessive chemical fertilisers and to avoid spraying pesticides near water bodies.

When communities actively participate in such actions, water bodies remain cleaner and healthier for all.

Potable water is water that is safe and fit for drinking. It should not harm our health when consumed.

The main characteristics of potable water are:

• It should be clear and colourless, without any suspended impurities like mud or visible particles.
• It should be free from harmful germs such as bacteria, viruses and parasites that cause diseases.
• It should not contain harmful chemicals, heavy metals or toxic substances above safe limits.
• It should have a pleasant taste and odour, not foul or metallic.
• It should contain a small amount of useful minerals like calcium and magnesium, which are good for health.

Thus, potable water is not completely pure distilled water, but it is free from substances that can harm our body.

There are several simple methods to make water safe for drinking at home.

• Boiling: Boiling water for 10–15 minutes kills most disease-causing germs.
  Advantage: Very effective and does not require any special chemical.
  Limitation: It does not remove dissolved salts or chemicals and requires fuel or electricity.
• Filtration: Passing water through a filter or cloth removes suspended impurities and some microorganisms.
  Advantage: Removes visible dirt and improves taste; simple to use.
  Limitation: Ordinary filters do not kill all germs, so water may still need further treatment.
• Chlorination: Adding a calculated amount of chlorine or bleaching powder kills germs present in water.
  Advantage: Suitable for disinfecting large amounts of water and is widely used in public supply.
  Limitation: Excess chlorine can give bad taste and may be harmful; the quantity must be carefully controlled.

Often, a combination of these methods is used to ensure drinking water is safe.

To obtain safe drinking water from muddy river water at home, the following steps can be followed:

• Sedimentation: First, allow the muddy water to stand undisturbed in a clean bucket. The heavier mud particles will slowly settle down at the bottom.
• Decantation: Gently pour the clear upper layer of water into another clean vessel, leaving the muddy layer behind.
• Filtration: Pass the decanted water through a clean cloth, sand filter or a household filter to remove remaining suspended particles.
• Boiling: Boil the filtered water for about 10–15 minutes to kill harmful germs.
• Chlorination (optional): After cooling, add a chlorine tablet in the correct quantity if recommended. This gives extra safety against germs.

Finally, store the clean water in a covered, hygienic container and use a clean ladle or tap to take water out. This process makes the water safe for drinking.

Freshwater on Earth is limited, and many regions face water scarcity. As population and demand increase, conserving water becomes very important to ensure that everyone gets enough clean water now and in future.

Methods to save water at home:

• Closing taps properly and repairing leaking taps and pipes.
• Using a bucket and mug for bathing instead of a shower.
• Reusing relatively clean water, such as water used for washing vegetables, to water plants.
• Not wasting water while brushing teeth or washing utensils.

Methods to save water in school:

• Checking school taps and tanks regularly for leaks.
• Using buckets and mops instead of flowing water hoses to clean floors.
• Organising awareness campaigns and putting up posters to remind everyone to save water.

By following these simple steps, we can reduce wastage and help in conserving this precious natural resource.

Sewage is wastewater from homes, offices, hospitals, industries and other buildings. It contains human excreta, food wastes, oils, detergents and many other impurities.

The main stages of sewage treatment in a sewage treatment plant (STP) are:

• Primary treatment: Sewage is first passed through screens to remove large objects like rags, sticks and plastics. Then it is allowed to stand in sedimentation tanks where heavy particles settle at the bottom as sludge and lighter materials float on the surface and are removed.
• Secondary treatment: The partially cleaned sewage is pumped into aeration tanks where air is blown into it. Beneficial microorganisms grow and break down the dissolved and suspended organic matter. The mixture is then sent to another tank where the microbes and remaining solids settle down.
• Tertiary treatment (if needed): The clear water from the top is disinfected using chlorine or other methods to kill harmful germs before being released into rivers or reused for irrigation and other purposes.

Thus, STPs reduce the pollution load of sewage and protect water bodies from contamination.

The 3R principle stands for Reduce, Reuse and Recycle. Following this principle helps to decrease the amount of waste produced and, in turn, reduces pollution.

• Reduce: Using fewer resources means less waste and less pollution. For example, reducing the use of plastic bags and disposable items reduces plastic waste in water bodies and landfills. Using less electricity reduces burning of fossil fuels in power plants, lowering air pollution.
• Reuse: Reusing items such as glass bottles, cloth bags and old containers reduces the need to make new products. This saves raw materials, energy and water used in manufacturing and also decreases the amount of garbage that can pollute air and water.
• Recycle: Recycling materials like paper, metal and plastic means converting old items into new products. Recycling paper saves trees, which improves air quality, and recycling metals and plastics reduces industrial waste and pollution.

By practising the 3Rs in daily life, we can reduce the load on sewage systems, decrease air and water pollution and conserve natural resources.

A septic tank is an underground chamber used for sewage treatment in places where there is no central sewage system, such as villages and isolated houses.

Wastewater from toilets and bathrooms flows through pipes into the septic tank. Inside the tank, heavy solid particles settle at the bottom as sludge, while lighter materials like oil and grease float on the surface as scum. Anaerobic bacteria present in the tank partially decompose the organic matter. The relatively clear liquid in the middle flows out into a soak pit or drain field where it slowly seeps into the soil and gets further purified by soil organisms.

Advantages for rural areas:

• It does not require long pipelines or large treatment plants and is suitable for scattered houses.
• It is simple to operate and does not need continuous electricity supply.
• It prevents direct discharge of sewage into ponds and open fields, thereby reducing water pollution and spread of diseases.

However, septic tanks must be constructed and maintained properly to function efficiently.

Proper wastewater management means collecting, treating and safely disposing of or reusing wastewater from homes, industries and other sources. It plays a very important role in protecting the environment and human health.

When wastewater is treated before being released, most harmful germs and pollutants are removed. This prevents contamination of rivers, lakes and groundwater and reduces the spread of water-borne diseases like cholera and typhoid. Treated water can be reused for irrigation, gardening and some industrial processes, saving freshwater.

In addition, safe disposal of sewage prevents foul smell, breeding of flies and mosquitoes and maintains cleanliness in neighbourhoods. Thus, proper wastewater management helps in keeping our surroundings clean, conserving water and ensuring a healthy life for people and other living organisms.

The government plays a key role in controlling pollution by making laws, setting standards and ensuring their proper implementation. Pollution control boards are set up to monitor air and water quality in different regions.

The government can:

• Fix limits for the amount of pollutants that factories and vehicles can release.
• Make it compulsory for industries to treat their waste before discharging it into rivers or the atmosphere.
• Declare certain regions as special areas where only non-polluting industries are allowed.
• Start programmes for cleaning polluted rivers and planting trees along roads and in cities.

Laws related to air and water pollution give the government the power to fine or close down units that do not follow the rules. However, laws alone are not enough. People must also cooperate and support government efforts to keep the environment clean.

Public awareness is necessary because pollution is often caused by the daily actions of ordinary people, such as using vehicles, burning waste or throwing garbage in open places. If people do not understand the harmful effects of pollution, they may not be willing to change their habits.

Role of community: Residents of an area can form groups to keep their locality clean, organise cleanliness drives and stop others from dumping waste in drains or water bodies. They can also cooperate with local authorities in tree plantation and waste collection programmes.

Role of NGOs (Non-Governmental Organisations): NGOs conduct awareness campaigns, street plays, rallies and workshops to educate people about pollution and ways to reduce it. They may also file complaints or court cases against industries or agencies that pollute the environment and work with schools and government departments on environmental projects.

When people become aware and actively participate, control of pollution becomes more effective and long-lasting.

As a Class 8 student, I can play an important role in reducing pollution of air and water in my neighbourhood by following and promoting a simple action plan:

• At home: I will avoid wasting water, close taps properly and persuade my family members to repair any leaking pipes. I will request my parents to use public transport or share vehicles whenever possible and not to burn garbage or dry leaves.
• In school: I will participate in eco-club activities, tree plantation drives and cleanliness campaigns. I will help in keeping the school premises clean and prevent littering in toilets and around water taps.
• In the community: Along with my friends, I can make posters and slogans about saving water and keeping air clean and display them in our locality. We can talk politely to shopkeepers and neighbours about using dustbins and avoiding plastic bags.
• Personal habits: I will use a bicycle or walk for short distances instead of demanding a lift on a scooter or car. I will refuse to burst too many firecrackers during festivals and encourage eco-friendly celebrations.

Though these steps appear small, if many students and families follow such an action plan, pollution in our neighbourhood can be reduced considerably and the environment will become healthier.