Class 8 Science Notes Chapter 18 (Chapter 18) – Examplar Problems Book
Alright class, let's focus on Chapter 18, "Pollution of Air and Water," from your Science Exemplar book. This is a crucial chapter, not just for your exams but also for understanding the environmental challenges we face. Pay close attention as these concepts frequently appear in various government exams.
Chapter 18: Pollution of Air and Water - Detailed Notes
1. Introduction to Pollution
- Pollution: The contamination of the environment (air, water, soil) with harmful substances, called pollutants, which adversely affect living organisms and the environment.
- Pollutants: Substances that cause pollution. They can be natural (e.g., volcanic ash, forest fires) or man-made (e.g., industrial waste, vehicle emissions).
2. Air Pollution
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Definition: The contamination of air by unwanted substances that have harmful effects on both living organisms and non-living components.
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Air Pollutants: Substances present in the atmosphere in concentrations harmful to living beings and the environment.
- Sources of Air Pollution:
- Natural: Forest fires, volcanic eruptions, dust storms.
- Man-made: Factories, power plants, vehicle exhausts, burning of firewood and dung cakes, mining activities, agricultural activities (pesticide spraying), burning of garbage.
- Major Air Pollutants and their Effects:
- Carbon Monoxide (CO): Produced by incomplete combustion of fuels (like petrol, diesel in vehicles). It's a poisonous gas that reduces the oxygen-carrying capacity of blood.
- Sulphur Dioxide (SO2): Produced mainly by burning coal in power plants and industries. Causes respiratory problems (asthma, bronchitis), irritation to the eyes, and contributes significantly to acid rain.
- Nitrogen Oxides (NOx): Produced from high-temperature combustion in vehicle engines and power plants. Contributes to smog and acid rain.
- Suspended Particulate Matter (SPM): Tiny solid particles or liquid droplets suspended in the air (e.g., dust, soot, smoke). Produced by industries, vehicles, construction sites. Reduces visibility, causes respiratory diseases.
- Chlorofluorocarbons (CFCs): Used in refrigerators, air conditioners, and aerosol sprays. Damage the ozone layer in the atmosphere, which protects us from harmful ultraviolet (UV) radiation from the sun. (Note: CFCs are now largely phased out under international agreements like the Montreal Protocol, replaced by HFCs, which are potent greenhouse gases).
- Carbon Dioxide (CO2): A major greenhouse gas. While essential for photosynthesis, excess CO2 (from burning fossil fuels, deforestation) traps heat in the atmosphere, leading to global warming.
- Methane (CH4): Another potent greenhouse gas, produced from decomposition of organic matter in landfills, agriculture (paddy fields, livestock).
- Smog: A thick fog-like layer in the atmosphere, especially during winters. It is formed by the combination of smoke and fog. Contains pollutants like nitrogen oxides and other air pollutants. Causes breathing difficulties like asthma, cough, and wheezing.
- Acid Rain: Oxides of sulphur (SO2) and nitrogen (NOx) react with water vapour present in the atmosphere to form sulphuric acid (H2SO4) and nitric acid (HNO3). These acids come down with rain, making the rain acidic.
- Effects of Acid Rain: Damages buildings and monuments (like the Taj Mahal - marble cancer), corrodes metals, harms plants and aquatic life, makes soil acidic.
- Greenhouse Effect: The natural process where certain gases (greenhouse gases like CO2, CH4, water vapour, N2O) in the atmosphere trap the sun's heat, keeping the Earth warm enough for life.
- Global Warming: The gradual increase in the overall temperature of the Earth's atmosphere generally attributed to the enhanced greenhouse effect caused by increased levels of carbon dioxide, CFCs, and other pollutants.
- Consequences: Melting of glaciers and polar ice caps, rise in sea level, changes in rainfall patterns, impacts on agriculture and ecosystems.
- Ozone Layer Depletion: The thinning of the ozone layer (O3) in the stratosphere, primarily caused by CFCs. This allows more harmful UV radiation to reach the Earth's surface, increasing the risk of skin cancer, cataracts, and damage to plants.
- Case Study - The Taj Mahal: The white marble of the Taj Mahal is being corroded and yellowed due to acid rain (caused by SO2 and NOx emissions from nearby industries like the Mathura oil refinery and vehicles) and soot particles. This phenomenon is often called 'Marble Cancer'. Steps taken include banning polluting industries nearby, promoting cleaner fuels (CNG), and cleaning the marble surface.
- Sources of Air Pollution:
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Prevention and Control of Air Pollution:
- Switching to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas).
- Using unleaded petrol in vehicles.
- Regular pollution checks for vehicles.
- Adopting renewable energy sources (solar, wind, hydro).
- Afforestation (planting more trees) - Trees absorb CO2.
- Installing tall chimneys with filters in factories.
- Proper disposal of garbage instead of burning.
- Using public transport, carpooling, cycling, walking.
- Creating public awareness (e.g., Van Mahotsav).
3. Water Pollution
- Definition: The contamination of water bodies (like rivers, lakes, oceans, groundwater) by substances harmful to life.
- 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: Chemical pollutants discharged from factories and industries (acids, alkalis, heavy metals like lead, mercury, arsenic, cadmium, oils, grease). Often toxic.
- Agricultural Runoff: Excess fertilizers (nitrates, phosphates) and pesticides (DDT, etc.) washed off from fields into water bodies.
- Domestic Waste: Detergents, plastics, garbage thrown into water bodies.
- Oil Spills: Accidental discharge of petroleum into oceans/rivers.
- Thermal Pollution: Discharge of hot water from power plants and industries, reducing dissolved oxygen in the water.
- Effects of Water Pollution:
- Waterborne Diseases: Caused by pathogenic microorganisms in contaminated water (e.g., Cholera, Typhoid, Jaundice, Dysentery, Polio).
- Eutrophication: Excessive richness of nutrients (especially nitrates and phosphates from fertilizers and sewage) in a lake or other body of water, frequently due to runoff from the land. This causes a dense growth of algae (algal bloom). When these algae die, their decomposition by bacteria consumes large amounts of dissolved oxygen, leading to the death of fish and other aquatic animals.
- Biomagnification: The increasing concentration of toxic substances (like pesticides, heavy metals) in the tissues of organisms at successive higher levels in a food chain.
- Harm to Aquatic Life: Chemical pollutants can directly kill fish and other aquatic organisms. Reduced dissolved oxygen (due to sewage decomposition or thermal pollution) also causes mortality. Plastics can entangle or be ingested by aquatic animals.
- Groundwater Contamination: Harmful chemicals (like arsenic, fluorides, nitrates from fertilizers/pesticides) can seep into the ground and contaminate groundwater, making it unfit for drinking.
- Case Study - The Ganga: The river Ganga is heavily polluted by untreated sewage, industrial effluents, agricultural runoff, dumping of garbage, dead bodies, and idols. The Ganga Action Plan was launched in 1986 (and subsequent phases/programs like Namami Gange) to reduce pollution levels.
- Potable Water: Water that is safe and suitable for drinking.
- Water Purification: Methods to make water safe for drinking:
- Filtration: Removing suspended impurities using filters (e.g., candle type filter, modern RO systems often include filters).
- Boiling: Kills most harmful microorganisms. Simplest method for household purification.
- Chlorination: Adding chlorine tablets or bleaching powder to kill germs. Commonly used in municipal water supply.
- UV Radiation: Using ultraviolet light to kill microorganisms. Used in many modern water purifiers.
- Water Conservation - The 3 R's:
- Reduce: Minimize water usage (e.g., turn off taps while brushing, fix leaks).
- Reuse: Use water for multiple purposes (e.g., water used for washing vegetables can be used for watering plants).
- Recycle: Treat wastewater to make it usable again (usually for non-potable purposes like irrigation or industrial cooling).
- Individual Role:
- Do not waste water.
- Do not dispose of oils, paints, medicines, or chemicals down the drain or toilet.
- Minimize use of pesticides and fertilizers.
- Properly dispose of waste; avoid throwing garbage into water bodies.
- Participate in awareness programs.
Key Takeaways for Exams:
- Know the definitions of pollution, pollutants, air pollution, water pollution, potable water.
- Identify major air and water pollutants, their sources, and specific effects (e.g., CO effect on blood, SO2/NOx role in acid rain, CFCs role in ozone depletion, excess CO2 role in global warming, pathogens in waterborne diseases, nutrients in eutrophication).
- Understand the concepts of Acid Rain, Greenhouse Effect, Global Warming, Ozone Layer Depletion, Eutrophication, and Biomagnification.
- Be familiar with the Taj Mahal and Ganga case studies.
- Know various methods of water purification and air/water pollution control.
- Understand the importance of conservation (3 R's).
Now, let's test your understanding with some multiple-choice questions.
Multiple Choice Questions (MCQs)
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Which of the following gases is primarily responsible for reducing the oxygen-carrying capacity of blood?
(a) Carbon dioxide (CO2)
(b) Sulphur dioxide (SO2)
(c) Carbon monoxide (CO)
(d) Nitrogen dioxide (NO2) -
Acid rain is mainly caused by the atmospheric pollution of:
(a) Oxides of sulphur and nitrogen
(b) Carbon dioxide and carbon monoxide
(c) Methane and ozone
(d) Chlorofluorocarbons (CFCs) -
The phenomenon responsible for the corrosion of the marble of the Taj Mahal is often referred to as:
(a) Eutrophication
(b) Global Warming
(c) Marble Cancer
(d) Ozone Depletion -
Which of the following is NOT a greenhouse gas?
(a) Carbon dioxide (CO2)
(b) Methane (CH4)
(c) Nitrogen (N2)
(d) Water vapour (H2O) -
Excessive nutrients (like nitrates and phosphates) in a water body lead to a condition called:
(a) Biomagnification
(b) Eutrophication
(c) Chlorination
(d) Sedimentation -
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 -
Chlorofluorocarbons (CFCs) were widely used in refrigerators and air conditioners, but they are harmful because they:
(a) Cause acid rain
(b) Lead to eutrophication
(c) Deplete the ozone layer
(d) Increase the greenhouse effect significantly -
Which of the following diseases is typically spread through contaminated water?
(a) Asthma
(b) Scurvy
(c) Cholera
(d) Tuberculosis -
The Ganga Action Plan was initiated primarily to:
(a) Build more dams on the Ganga
(b) Promote tourism along the Ganga
(c) Reduce the pollution levels in the Ganga
(d) Increase fishing activities in the Ganga -
Which method is commonly used at the household level to kill germs in drinking water?
(a) Sedimentation
(b) Chlorination
(c) Filtration using cloth
(d) Boiling
Answers to MCQs:
- (c) Carbon monoxide (CO)
- (a) Oxides of sulphur and nitrogen
- (c) Marble Cancer
- (c) Nitrogen (N2) - While nitrogen gas makes up ~78% of the air, it is not considered a greenhouse gas in its diatomic form (N2). Nitrous oxide (N2O) is a greenhouse gas.
- (b) Eutrophication
- (b) Water that is pure and safe for drinking
- (c) Deplete the ozone layer
- (c) Cholera
- (c) Reduce the pollution levels in the Ganga
- (d) Boiling
Study these notes thoroughly. Remember the specific pollutants, their sources, effects, and the control measures. Understanding the underlying processes like acid rain formation or eutrophication is key. Good luck with your preparation!