Pollution and pollutants
A heap of plastic and rotting garbage near a stream makes the water dirty, the air smelly and the place unhealthy. When the surroundings become harmful like this, we say the environment is polluted.
Pollution (प्रदूषण) is the contamination of the natural environment in a way that harms ecosystems. Pollutants (प्रदूषके) are the factors that cause it.
In the figure : In the figure a volcano and pollen are natural pollutants, while a factory, pesticides, vehicles and sewage are man-made pollutants. Nature destroys natural pollutants in time, but not man-made ones.
Rule 1: Pollutants: natural and man-made — Pollutants affect the natural functions of an ecosystem and harm living (biotic) and non-living (abiotic) factors. Natural pollutants (volcanic ash, pollen) are broken down by nature in due course. Man-made pollutants (plastic, pesticides, factory waste) are not.
- Easy : Pollen is a natural pollutant; a plastic bag is a man-made one.
- Medium : A rotting fallen leaf vanishes in a few weeks, but a plastic bottle stays for years. This shows why man-made pollutants are the bigger problem.
- Exam-type : Out of 10 items in a classroom dustbin, 7 are plastic wrappers and 3 are paper and peel. Man-made pollutants are 7 out of 10, that is 70 percent.
In the figure : In the figure industrialization, mining, transport, a growing population and the overuse of pesticides and fertilizers cause pollution.
Rule 2: Causes of pollution — Industrialization, increasing population, mining, transportation, and the overuse of pesticides and fertilizers pollute the earth.
- Easy : More vehicles on the road mean more smoke.
- Medium : If one factory makes 20 kg of waste a day, then 5 such factories make 5 × 20 = 100 kg a day.
- Exam-type : A town grows from 40000 to 60000 people. If each person makes 0.5 kg of waste a day, daily waste rises from 20000 kg to 30000 kg, an increase of 10000 kg.
Pollution harms the environment. Natural pollutants are destroyed by nature; man-made ones are not.
Thinking all pollutants are man-made. Volcanoes and pollen are natural pollutants.
Memory clue: "Natural = Nature cleans; Man-made = Man must clean".
Spot the difference
| Type | Example | Destroyed by nature? |
|---|---|---|
| Natural | Volcano, pollen | Yes |
| Man-made | Pesticides, sewage | No |
Practice questions
- 1What is pollution?
- 2What are pollutants?
- 3Name two natural pollutants.
- 4Name two man-made pollutants.
- 5Which pollutants does nature not destroy?
- 6List three human activities that cause pollution.
- 7A bin has 12 items and 9 are plastic. What percent are plastic?
- 8Why are man-made pollutants a bigger problem than natural ones?
Show answers (try them yourself first)
- 1Contamination of the natural environment that harms ecosystems.
- 2Factors that affect the natural functions of an ecosystem and harm living and non-living factors.
- 3Volcanic eruption and pollen.
- 4Pesticides and vehicle smoke (or sewage, factory waste).
- 5Man-made pollutants.
- 6Mining, transport and overuse of pesticides and fertilizers (or industrialization).
- 79 ÷ 12 × 100 = 75 percent
- 8Nature does not destroy them in time, so they keep building up and harm living things.
Air pollution: causes and effects
On a day when someone burns a pile of dry leaves near your house, you cough and your eyes sting. The air has become unclean. Some such dirt in the air comes from nature, but much of it comes from our own actions.
Air pollution (वायुप्रदूषण) is the contamination of air by harmful substances such as poisonous gases, smoke, particulate matter and microbes.
In the figure : In the figure air is polluted naturally by volcanoes, dust storms and forest fires, and by man-made causes such as vehicles, burning waste and atomic blasts.
Rule 1: Causes of air pollution — Natural causes: volcanic eruptions (hydrogen sulphide, sulphur dioxide, carbon dioxide, dust), earthquakes (poisonous gases), cyclones and dust storms (dust, soil, pollen, microbes), forest fires (carbon dioxide, sulphur dioxide, smoke), and spores of bacteria and fungi. Man-made causes: burning of fuels (coal, timber, LPG, kerosene, diesel, petrol) giving carbon dioxide, carbon monoxide, oxides of nitrogen, sulphur dioxide and lead compounds; burning of solid and agricultural waste; factories; atomic energy plants and blasts that release radiations.
- Easy : A forest fire adds smoke and carbon dioxide to the air; it is a natural cause.
- Medium : A vehicle burning petrol releases carbon monoxide; this is a man-made cause.
- Exam-type : If a vehicle puts out 2 g of smoke particles in a km, then 500 such vehicles driving 10 km put out 500 × 10 × 2 = 10000 g, that is 10 kg.
In the figure : In the figure sulphur dioxide irritates the eyes, carbon monoxide lowers the oxygen carried by blood, dust causes silicosis and polluted air turns leaves yellow.
Rule 2: Effects of air pollution — Sulphur dioxide irritates the eyes and respiratory tract. Carbon monoxide lowers the oxygen-carrying capacity of blood. Dust causes silicosis. Methane causes poisoning and asthma. In plants the stomata close, photosynthesis slows and leaves turn yellow. In animals respiration and eyes are affected.
- Easy : Sulphur dioxide stings the eyes and throat.
- Medium : Closed stomata mean less carbon dioxide enters a leaf, so photosynthesis slows and the leaf turns yellow.
- Exam-type : The Bhopal gas leak on the night of 2 December 1984 was the worst industrial accident, and it killed thousands of people. In London in December 1952 smog lasted 5 days. Both show why industries must be careful.
Air pollution comes from natural and man-made causes. Effects: eyes, breathing, blood, plants.
Thinking only factories pollute air. Burning waste and vehicles also do, as do volcanoes.
Memory clue: "CO steals Oxygen, SO2 Stings".
Spot the difference
| Pollutant | Effect |
|---|---|
| Sulphur dioxide | Irritates eyes and respiratory tract |
| Carbon monoxide | Less oxygen in blood |
| Dust | Silicosis |
| Methane | Poisoning, asthma |
Practice questions
- 1What is air pollution?
- 2Name two natural causes of air pollution.
- 3Name two fuels whose burning pollutes air.
- 4Which gas lowers the oxygen-carrying capacity of blood?
- 5Which disease is caused by dust?
- 6What happens to the stomata of plants in polluted air?
- 7300 vehicles each give out 3 g of smoke per km. How much smoke do they give out in 4 km?
- 8Why is burning farm waste in the open harmful even though it is a quick way to clear a field?
Show answers (try them yourself first)
- 1Contamination of air by harmful gases, smoke, particles and microbes.
- 2Volcanic eruption and forest fire (or dust storm).
- 3Coal and petrol (or diesel, kerosene).
- 4Carbon monoxide
- 5Silicosis
- 6They close, photosynthesis slows and leaves turn yellow.
- 7300 × 3 × 4 = 3600 g (3.6 kg)
- 8It releases smoke and gases such as carbon monoxide and carbon dioxide into the air and harms breathing, eyes and plants.
Ozone, green house effect, acid rain and prevention
Wearing a thin jacket on a sunny day feels warm, and a car parked in the sun with closed windows gets very hot inside. The air around the earth also traps heat like a blanket. But when this blanket becomes too thick, the earth warms too much.
The ozone layer (ओझोन थर) protects us from the sun's UV-B rays. Global warming (जागतिक तापमानवाढ) is the rise in the earth's temperature because of greenhouse gases. Acid rain (आम्ल पाऊस) is rain that contains acids.
In the figure : In the figure the ozone layer absorbs the harmful UV-B rays of the sun and protects living things on the earth.
Rule 1: The ozone layer — The ozone layer protects living things from the sun's ultraviolet (UV-B) rays, but it is getting depleted.
- Easy : The ozone layer works like sunscreen for the whole earth.
- Medium : If the ozone layer is damaged, more UV-B reaches the earth, which can harm skin and eyes of living things.
- Exam-type : Reason out: CFC (from old fridges and sprays) depletes the ozone layer, so controlling or banning CFC protects the layer.
In the figure : In the figure greenhouse gases (CO₂, CH₄, N₂O, CFC) trap the heat coming from the earth and send part of it back, which warms the earth.
Rule 2: Greenhouse effect — Carbon dioxide, though present in a small quantity, absorbs solar heat, and its proportion has risen in the last 100 years because of industrialization. Nitrous oxide, methane and CFC also trap heat. Together they are greenhouse gases (हरितगृह वायू).
- Easy : CO₂, CH₄, N₂O and CFC are greenhouse gases.
- Medium : Count the greenhouse gases named here: CO₂, CH₄, N₂O and CFC make 4.
- Exam-type : Planting trees helps because plants take in carbon dioxide during photosynthesis, which lowers its proportion in the air.
In the figure : In the figure more greenhouse gases cause global warming, which melts glaciers and raises the sea level.
Rule 3: Global warming — Greenhouse gases raise the global temperature. This disturbs agriculture and wild animals, and melts glaciers, which raises the sea level.
- Easy : Melting glaciers raise the sea level.
- Medium : Sea level rising by 2 mm every year rises by 2 × 10 = 20 mm in 10 years.
- Exam-type : Cause to effect chain: more CO₂ → more heat trapped → warmer earth → glaciers melt → sea level rises.
In the figure : In the figure oxides of sulphur and nitrogen in smoke form acids in rain water; acid rain corrodes buildings and harms aquatic life.
Rule 4: Acid rain — Oxides of sulphur and nitrogen from burning coal, timber and fuel oils mix with rain water and form sulphuric, nitric and nitrous acids. Acid rain makes soil and water acidic, harms aquatic life and plants, corrodes buildings and monuments, and lets heavy metals such as mercury and cadmium enter the food chain.
- Easy : Burning coal gives sulphur dioxide, which can form acid rain.
- Medium : Two acids in acid rain are sulphuric acid and nitric acid.
- Exam-type : Old marble and stone monuments get eaten away slowly by acid rain, so cities with many factories need filters on chimneys to protect them.
In the figure : In the figure air pollution is controlled by filters in factory chimneys, proper disposal of waste and control or a ban on CFC.
Rule 5: Preventing air pollution — Use arresters and filters in factories, dispose of stinking waste properly, control atomic tests and chemical weapons, and control or ban CFC production. The Air Quality Index (AQI, हवेची गुणवत्ता निर्देशांक) is measured every day from the proportion of SO2, CO, NO2, ozone and particulate matter.
- Easy : Filters on chimneys hold back smoke particles.
- Medium : The AQI uses 5 pollutants: SO2, CO, NO2, ozone and particulate matter.
- Exam-type : On a day with a poor AQI, a sensible person avoids long outdoor exercise and does not burn leaves or waste.
Ozone, green house effect, acid rain and prevention
In the app you can move this figure with your finger.
Open in the appOzone protects from UV-B. Greenhouse gases cause global warming. SO₂ and nitrogen oxides cause acid rain.
Mixing up ozone depletion and global warming. The first is about UV-B rays; the second is about trapped heat.
Memory clue: "Ozone = Umbrella, CO₂ = Blanket, SO₂ = Sour rain".
Spot the difference
| Topic | Cause | Effect |
|---|---|---|
| Ozone depletion | CFC | More UV-B |
| Global warming | CO₂, CH₄, N₂O, CFC | Melting glaciers |
| Acid rain | Oxides of S and N | Corrodes monuments |
Practice questions
- 1What does the ozone layer protect us from?
- 2Name two greenhouse gases.
- 3What is global warming?
- 4Which gases cause acid rain?
- 5Name two acids found in acid rain.
- 6What does AQI stand for and how is it measured?
- 7Sea level rises 3 mm every year. How much will it rise in 15 years?
- 8Explain how acid rain harms a lake and a monument.
Show answers (try them yourself first)
- 1The sun's ultraviolet (UV-B) rays.
- 2Carbon dioxide and methane (or nitrous oxide, CFC).
- 3The rise in the earth's temperature caused by greenhouse gases.
- 4Oxides of sulphur and nitrogen.
- 5Sulphuric acid and nitric acid.
- 6Air Quality Index; from the daily proportion of SO₂, CO, NO₂, ozone and particulate matter.
- 73 × 15 = 45 mm
- 8It makes the lake water acidic, harming aquatic life, and it corrodes the monument's stone and metal.
Water pollution
A river flowing through a city can turn dark and foamy when drains, factory water and washed clothes empty into it. Fish float dead on the surface and people who use the water fall ill.
Water pollution (जलप्रदूषण) occurs when water becomes unclean and poisonous, its oxygen decreases or it spreads epidemic diseases.
In the figure : In the figure water pollutants are biological (germs, algae), inorganic (sand, compounds of metals) or organic (pesticides, sewage).
Rule 1: Types and causes — Biological pollutants: algae, bacteria, viruses, parasites. Inorganic pollutants: fine sand, dust, soil, salts and compounds of arsenic, cadmium, lead and mercury. Organic pollutants: weedicides, insecticides, fertilizers, sewage and industrial effluents. Natural causes: aquatic weeds, decomposing matter, mud, soil erosion, microbes, algae and nematodes. Man-made causes: domestic sewage, industrial effluents, oil spillage, fertilizers and pesticides, human wastes, washing clothes, ashes and floral offerings.
- Easy : Sewage is an organic pollutant of water.
- Medium : Fine sand in water is an inorganic pollutant; algae are a biological pollutant.
- Exam-type : Tanning centres made the Palar river a 'gutter river'. This shows how one industry can pollute a whole river.
In the figure : In the figure polluted water has less dissolved oxygen, so aquatic animals die; in this sample the sewage drain has the least.
Rule 2: Effects of water pollution — Hepatitis, typhoid and skin diseases spread through polluted water. Heavy metals can cause ailments of the liver, kidneys and brain. Plant growth is retarded, dissolved oxygen decreases, and aquatic animals die.
- Easy : Less dissolved oxygen means fish cannot breathe.
- Medium : Typhoid and hepatitis spread by drinking polluted water, so boil or filter water when unsure.
- Exam-type : Three samples show dissolved oxygen of 7, 5 and 2 mg per litre. The sample with 2 is the most polluted, and 7 − 2 = 5 mg per litre less than the cleanest.
Water pollutants: biological, inorganic, organic. Pollution lowers dissolved oxygen.
Thinking clear water is always clean. Dissolved metals and germs may not be visible.
Memory clue: "B-I-O = Biological, Inorganic, Organic".
Spot the difference
| Type | Examples |
|---|---|
| Biological | Algae, bacteria, viruses |
| Inorganic | Sand, salts, lead, mercury compounds |
| Organic | Pesticides, sewage, fertilizers |
Practice questions
- 1When is water said to be polluted?
- 2Name the three types of water pollutants.
- 3Name two natural causes of water pollution.
- 4Name two man-made causes of water pollution.
- 5Name two diseases spread by polluted water.
- 6Why do fish die in polluted water?
- 7Dissolved oxygen is 8 mg per litre in a clean pond and 3 mg per litre in a drain. Find the difference.
- 8Why is dumping floral offerings and washing clothes directly in a river a problem, and what is a better way?
Show answers (try them yourself first)
- 1When it becomes unclean and poisonous, its oxygen decreases or it spreads epidemic diseases.
- 2Biological, inorganic and organic.
- 3Soil erosion and decomposing matter (or aquatic weeds).
- 4Domestic sewage and industrial effluents (or oil spillage).
- 5Typhoid and hepatitis.
- 6Dissolved oxygen decreases.
- 78 − 3 = 5 mg per litre
- 8They add organic waste and chemicals that lower oxygen; a better way is collecting offerings for composting and washing away from the river.
Soil pollution and pollution control laws
Fertile black soil gives good crops. But if factory water full of salt is poured on it year after year, the soil becomes poor and the plants wither. Soil is as precious as water and air.
Soil pollution (मृदाप्रदूषण) is the change in the physical, biological and chemical properties of soil that lowers its fertility.
In the figure : In the figure air, water and soil pollution are linked: sprays and gases pass between soil and air, acid rain reaches water, and fertilizers and wet waste pollute water.
Rule 1: Soil pollution and links — Salty and acidic industrial water lower soil fertility. Radioactive and other pollutants pass along the food chain to the human body, and toxic substances leach into water. The three types of pollution are linked: wet waste dumped at wrong places breeds pathogens that pollute water; sprayed insecticides and weedicides mix with air; chemical fertilizers pollute water; human and animal wastes give stinking gases.
- Easy : Salty factory water makes soil less fertile.
- Medium : Fertilizer on a field can wash into a nearby stream, so soil pollution becomes water pollution.
- Exam-type : Chain: pesticide sprayed on crops → settles on soil → washes into water → enters the food chain → reaches humans.
In the figure : In the figure the Water Pollution Prevention Act (1974), the Air Pollution Prevention Act (1981) and the Environmental Protection Act (1986) control pollution.
Rule 2: Laws and boards — Laws: Water Pollution Prevention Act (1974), Air Pollution Prevention Act (1981) and Environmental Protection Act (1986). The Maharashtra Pollution Control Board and the Central Pollution Control Board supervise whether industries and local bodies follow the laws.
- Easy : The Air Pollution Prevention Act is of 1981.
- Medium : From 1974 to 1986 is 1986 − 1974 = 12 years between the first and last of these three laws.
- Exam-type : What can you do as a student: use cloth bags instead of plastic, compost wet kitchen waste, plant trees, and report dumping or smoke to elders or the local body.
Soil, water and air pollution are linked. Laws: 1974 water, 1981 air, 1986 environment.
Mixing up the years of the laws. Order is water 1974, air 1981, environment 1986.
Memory clue: "Water, Air, Environment = 74, 81, 86".
Spot the difference
| Law | Year |
|---|---|
| Water Pollution Prevention Act | 1974 |
| Air Pollution Prevention Act | 1981 |
| Environmental Protection Act | 1986 |
Practice questions
- 1When is soil said to be polluted?
- 2What kind of industrial water lowers soil fertility?
- 3In which year was the Water Pollution Prevention Act passed?
- 4Name the law of 1986.
- 5Which boards supervise the pollution laws in Maharashtra and India?
- 6How does wet waste dumped at a wrong place pollute water?
- 7How many years after the Water Act was the Air Act passed?
- 8Explain with an example how air, water and soil pollution are linked.
Show answers (try them yourself first)
- 1When its physical, biological and chemical properties change and fertility decreases.
- 2Salty and acidic water.
- 31974
- 4Environmental Protection Act
- 5The Maharashtra Pollution Control Board and the Central Pollution Control Board.
- 6It breeds pathogens that reach water.
- 71981 − 1974 = 7 years
- 8Sprayed pesticide mixes with air, settles on soil, and washes into water, so one pollutant harms all three.
Quick revision
- Pollutants may be natural or man-made; nature destroys only the natural ones.
- Green house gases cause global warming; oxides of sulphur and nitrogen cause acid rain.
- Water, air and soil pollution are linked; laws of 1974, 1981 and 1986 control pollution.