Class 8 Science Notes Chapter 18 (Pollution of Air and Water) – Science Book
In this blog post, our focus will be on Chapter 18: Pollution of Air and Water. This is a crucial topic, not just for your exams but for understanding the world around us. Pay close attention, as questions from this chapter frequently appear in various government exams.
Chapter 18: Pollution of Air and Water - Detailed Notes
1. Pollution: The Basics
- Definition: Pollution is the contamination of the environment (air, water, soil) with harmful substances, called pollutants, which adversely affect living organisms and the environment.
2. Air Pollution
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Definition: The contamination of air by unwanted substances that have harmful effects on both living and non-living things.
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Air Pollutants: Substances that contaminate the air.
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Sources of Air Pollutants:
- Natural Sources: Forest fires, volcanic eruptions, dust storms, decay of organic matter.
- Man-made Sources:
- Factories and Power Plants: Release smoke, ash, sulfur dioxide (SO2), nitrogen oxides (NOx). Burning fossil fuels (coal, petroleum) is a major contributor.
- Vehicular Emissions: Release carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), unburnt hydrocarbons, and particulate matter.
- Burning of Firewood and Dung Cakes: Releases smoke and CO.
- Mining Activities: Release dust and particulate matter.
- Agricultural Activities: Use of pesticides and fertilizers can release harmful chemicals into the air.
- Use of Chlorofluorocarbons (CFCs): Previously used in refrigerators, air conditioners, and aerosols.
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Major Air Pollutants and Their Effects:
- Carbon Monoxide (CO):
- Source: Incomplete combustion of fuels (vehicles, firewood).
- Effect: Poisonous gas; reduces the oxygen-carrying capacity of blood, leading to respiratory problems, dizziness, and even death in high concentrations.
- Sulfur Dioxide (SO2):
- Source: Burning of coal in power plants and industries.
- Effect: Causes respiratory problems (asthma, bronchitis), irritation to eyes; contributes significantly to Acid Rain.
- Nitrogen Oxides (NOx):
- Source: Vehicular emissions, power plants.
- Effect: Contribute to smog and Acid Rain; cause respiratory issues.
- Particulate Matter (PM):
- Source: Dust, smoke from industries, vehicles, construction sites. Includes soot, fly ash.
- Effect: Reduces visibility; causes respiratory diseases when inhaled; fine particles can penetrate deep into the lungs.
- Chlorofluorocarbons (CFCs):
- Source: Refrigerants, aerosols (use now largely banned/regulated).
- Effect: Cause depletion of the Ozone Layer, which protects us from harmful ultraviolet (UV) radiation from the sun.
- Carbon Dioxide (CO2):
- While essential for photosynthesis, excess CO2 acts as a Greenhouse Gas.
- Source: Burning of fossil fuels, deforestation.
- Effect: Contributes to the Greenhouse Effect and Global Warming.
- Carbon Monoxide (CO):
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Specific Phenomena:
- Smog: A thick fog-like layer in the atmosphere, especially during winters, formed by smoke and fog. Contains pollutants like nitrogen oxides. Causes breathing difficulties (asthma, cough, wheezing).
- Acid Rain: Rainwater becomes acidic (pH < 5.6) due to the presence of dissolved sulfur dioxide (SO2) and nitrogen oxides (NOx), which react with water vapour to form sulfuric acid (H2SO4) and nitric acid (HNO3).
- Effects: Corrodes buildings and monuments (marble cancer), damages plants, makes soil acidic, harms aquatic life.
- Greenhouse Effect: The trapping of the sun's heat by certain gases (greenhouse gases like CO2, methane, nitrous oxide, water vapour) in the Earth's atmosphere, which keeps the planet warm enough for life. This is a natural phenomenon.
- Global Warming: The gradual increase in the average temperature of the Earth's atmosphere, primarily caused by the enhanced greenhouse effect due to increased concentrations of greenhouse gases from human activities (burning fossil fuels, deforestation).
- Effects: Melting of glaciers and polar ice caps, rise in sea levels, changes in rainfall patterns, extreme weather events, threats to ecosystems.
- Ozone Layer Depletion: Thinning of the ozone layer in the stratosphere caused by pollutants like CFCs. Allows more harmful UV radiation to reach the Earth's surface.
- Effects: Increased risk of skin cancer, cataracts, damage to plants and marine life. (Montreal Protocol is an international treaty to phase out ozone-depleting substances).
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Case Study: The Taj Mahal
- The white marble of the Taj Mahal is getting discoloured (yellowing) and corroded.
- Cause: Air pollution, primarily acid rain (due to SO2 and NOx from nearby industries like Mathura oil refinery and vehicles) and deposition of soot particles (suspended particulate matter - SPM). The reaction of acid rain with marble (calcium carbonate) causes corrosion, often termed 'Marble Cancer'.
- Steps Taken: Supreme Court directives led to switching to cleaner fuels (LPG, CNG) in industries and vehicles around the Taj Trapezium Zone (TTZ), restricting traffic, and relocating polluting industries.
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Prevention of Air Pollution:
- Use cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas).
- Promote renewable energy sources (solar, wind, hydro).
- Install tall chimneys with filters in factories.
- Improve engine efficiency and use catalytic converters in vehicles.
- Promote public transport, carpooling, cycling, and walking.
- Afforestation (planting more trees) – trees absorb CO2.
- Avoid burning dry leaves, trash, and agricultural waste; promote composting.
- Strict implementation of pollution control laws.
3. Water Pollution
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Definition: The contamination of water bodies (lakes, rivers, oceans, groundwater) by substances harmful to living organisms or which degrade water quality.
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Water Pollutants: Substances that contaminate water.
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Sources of Water Pollution:
- Sewage: Untreated domestic wastewater containing human excreta, food waste, detergents. Contains harmful microorganisms (bacteria, viruses, protozoa, parasites) and organic matter.
- Industrial Waste: Toxic chemicals (acids, alkalis, heavy metals like lead, mercury, arsenic, cadmium), oils, grease discharged from factories.
- Agricultural Runoff: Excess fertilizers (nitrates, phosphates) and pesticides (insecticides, herbicides) washed off from fields into water bodies.
- Solid Waste/Litter: Plastics, garbage dumped into water bodies.
- Oil Spills: Accidental discharge of petroleum into oceans or rivers.
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Major Water Pollutants and Their Effects:
- Sewage:
- Spreads waterborne diseases (Cholera, Typhoid, Jaundice, Dysentery).
- Decomposition of organic matter consumes dissolved oxygen, harming aquatic life.
- Industrial Chemicals (Heavy Metals - Arsenic, Lead, Fluorides):
- Highly toxic, accumulate in living organisms (Biomagnification).
- Cause various health problems (poisoning, developmental issues, skeletal fluorosis). Arsenic and fluoride contamination in groundwater is a major issue in parts of India.
- Fertilizers (Nitrates, Phosphates):
- Cause Eutrophication: Excessive growth of algae (algal bloom) due to nutrient enrichment. When algae die, their decomposition consumes large amounts of dissolved oxygen, leading to the death of fish and other aquatic animals.
- Pesticides:
- Toxic to aquatic life and humans.
- Can enter the food chain and biomagnify.
- Hot Water: Discharged from power plants and industries, reduces dissolved oxygen levels, affecting aquatic organisms.
- Sewage:
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Potable Water: Water that is safe for drinking.
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Water Purification: Methods to make water safe for drinking:
- Physical Methods:
- Filtration: Removing suspended impurities using filters (sand filters, filter paper, cloth, modern water purifiers).
- Boiling: Kills most harmful microorganisms.
- Chemical Methods:
- Chlorination: Adding chlorine tablets or bleaching powder to kill germs.
- UV Radiation: Modern purifiers use Ultraviolet light to kill germs without adding chemicals.
- Physical Methods:
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Case Study: The Ganga
- One of the world's most polluted rivers.
- Sources of Pollution: Untreated sewage from towns and cities, industrial effluents, dumping of garbage, religious offerings, immersion of ashes and idols.
- Impact: Threat to aquatic life, contamination of drinking water sources, spread of diseases.
- Ganga Action Plan (GAP): Launched in 1985 (later merged into National River Conservation Plan - NRCP and now under Namami Gange Programme) to reduce pollution levels. Aims included setting up sewage treatment plants (STPs).
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Prevention of Water Pollution:
- Treat sewage before discharging it into water bodies (Sewage Treatment Plants - STPs).
- Treat industrial effluents to remove harmful chemicals before release.
- Reduce, Reuse, and Recycle (especially plastics).
- Minimize the use of chemical fertilizers and pesticides; promote organic farming and integrated pest management.
- Conserve water – "Water is precious".
- Strict enforcement of laws regarding waste disposal.
- Public awareness and participation.
4. Individual Contribution
- Save energy (reduces fossil fuel burning).
- Use public transport/carpool/cycle/walk.
- Plant trees.
- Dispose of garbage properly; don't litter.
- Conserve water at home.
- Avoid using excessive pesticides/fertilizers in gardens.
- Report polluting activities.
Remember, understanding the sources, effects, and prevention methods for both air and water pollution is key for your exams. Focus on the specific pollutants, the phenomena like acid rain and eutrophication, and the case studies.
Multiple Choice Questions (MCQs)
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Which of the following gases is primarily responsible for the depletion of the Ozone layer?
(a) Carbon Dioxide (CO2)
(b) Sulfur Dioxide (SO2)
(c) Chlorofluorocarbons (CFCs)
(d) Carbon Monoxide (CO) -
Acid rain is mainly caused by the atmospheric pollution of:
(a) Carbon Monoxide and Carbon Dioxide
(b) Methane and Ozone
(c) Sulfur Dioxide and Nitrogen Oxides
(d) Chlorofluorocarbons and Carbon Dioxide -
The phenomenon where excessive nutrients in a water body cause dense growth of plant life (like algae) and death of animal life from lack of oxygen is called:
(a) Biomagnification
(b) Eutrophication
(c) Global Warming
(d) Chlorination -
Which of the following is NOT a greenhouse gas?
(a) Carbon Dioxide (CO2)
(b) Methane (CH4)
(c) Nitrogen (N2)
(d) Water Vapour (H2O) -
'Marble Cancer' affecting the Taj Mahal is primarily due to:
(a) Smog
(b) Ozone depletion
(c) Global Warming
(d) Acid Rain -
Potable water is defined as:
(a) Water collected directly from rain
(b) Water that is pure and safe for drinking
(c) Water used for industrial purposes
(d) Water found in oceans -
Which poisonous gas is produced due to incomplete combustion of fuels like petrol and diesel?
(a) Carbon Dioxide
(b) Nitrogen Oxide
(c) Sulfur Dioxide
(d) Carbon Monoxide -
The Ganga Action Plan was initiated primarily to:
(a) Build dams on the river Ganga
(b) Increase fishing activities in the Ganga
(c) Reduce the pollution levels in the river Ganga
(d) Promote tourism along the Ganga -
Which method is commonly used at homes to kill germs present in water to make it potable?
(a) Filtration
(b) Sedimentation
(c) Boiling
(d) Decantation -
Arsenic and Fluoride contamination in water is mainly associated with:
(a) Industrial effluents
(b) Sewage discharge
(c) Agricultural runoff
(d) Groundwater sources
Answer Key for MCQs:
- (c)
- (c)
- (b)
- (c)
- (d)
- (b)
- (d)
- (c)
- (c)
- (d)
Study these notes thoroughly. Understand the concepts, don't just memorize facts. Good luck with your preparation!