Pollution
Introduction
Pollution is the introduction of harmful substances (pollutants) into the environment that cause adverse effects. In ICSE Class 10 Biology, you study the different types of pollution, their effects, and control measures, along with global environmental issues.
Air Pollution
Major Air Pollutants
| Pollutant | Source | Effect |
|---|---|---|
| Carbon monoxide (CO) | Vehicle exhaust, incomplete combustion | Reduces oxygen-carrying capacity of blood |
| Sulphur dioxide (SO₂) | Coal burning, industrial processes | Respiratory problems, acid rain |
| Nitrogen oxides (NOₓ) | Vehicle engines, power plants | Acid rain, smog |
| Particulate matter (PM₂.₅, PM₁₀) | Dust, vehicle emissions, construction | Lung damage, respiratory diseases |
| Lead | Vehicle emissions (older vehicles) | Neurological damage |
| Ozone (ground-level) | Reaction of pollutants in sunlight | Respiratory irritation |
Effects of Air Pollution
- Respiratory diseases (asthma, bronchitis, lung cancer).
- Cardiovascular problems.
- Damage to crops and buildings.
- Acid rain and smog.
Water Pollution
Major Water Pollutants
| Pollutant | Source | Effect |
|---|---|---|
| Sewage | Domestic waste | Pathogens, oxygen depletion (eutrophication) |
| Industrial effluents | Factories | Toxic chemicals, heavy metals |
| Agricultural runoff | Fertilisers, pesticides | Nitrate/phosphate pollution, algal blooms |
| Oil spills | Tankers, offshore drilling | Marine life destruction |
| Plastics | Improper disposal | Ingestion by aquatic animals, microplastics |
Eutrophication
- Excess nutrients (nitrates, phosphates) enter water bodies from fertiliser runoff.
- Algae grow rapidly (algal bloom).
- Algae die and are decomposed by bacteria.
- Bacteria consume dissolved oxygen.
- Fish and other aquatic organisms die from oxygen depletion.
Soil Pollution
| Cause | Effect |
|---|---|
| Excessive fertilisers | Soil degradation, water contamination |
| Pesticides | Kill beneficial soil organisms |
| Industrial waste | Toxic chemical build-up |
| Plastic waste | Non-biodegradable, reduces soil fertility |
| Deforestation | Soil erosion |
Noise Pollution
| Source | Effect |
|---|---|
| Traffic, construction, factories | Hearing loss, stress, sleep disturbance |
| Loudspeakers, fireworks | Hypertension, irritability |
| Aircraft, trains | Communication interference |
Permissible noise levels: Day (55 dB residential, 75 dB industrial); Night (45 dB residential, 65 dB industrial).
Global Environmental Issues
Global Warming (Greenhouse Effect)
Greenhouse gases: CO₂, CH₄, N₂O, CFCs, water vapour.
Mechanism:
- Sunlight reaches the Earth's surface.
- Earth radiates heat (infrared radiation).
- Greenhouse gases trap some of this heat.
- This natural process keeps the Earth warm enough for life.
- Enhanced greenhouse effect (due to human activities) causes global temperature rise.
Effects: Rising sea levels, melting glaciers, extreme weather, loss of biodiversity.
Ozone Depletion
Cause: Chlorofluorocarbons (CFCs) from refrigerators, air conditioners, aerosol sprays.
Mechanism:
- CFCs rise to the stratosphere.
- UV radiation breaks CFCs, releasing chlorine atoms.
- Chlorine destroys ozone (O₃ → O₂).
- Each Cl atom can destroy thousands of ozone molecules.
Effects: Increased UV-B radiation → skin cancer, cataracts, reduced crop yield.
Acid Rain
Cause: SO₂ and NOₓ from burning fossil fuels react with water vapour to form sulphuric and nitric acids.
Effects:
- Damages leaves (forest dieback).
- Acidifies lakes and rivers (kills aquatic life).
- Corrodes buildings and monuments (e.g., Taj Mahal).
Pollution Control Measures
| Type | Control measures |
|---|---|
| Air | Use of cleaner fuels (CNG), catalytic converters, electrostatic precipitators |
| Water | Sewage treatment plants, industrial effluent treatment, reducing fertiliser use |
| Soil | Organic farming, bioremediation, proper waste disposal |
| Noise | Soundproofing, green buffers, noise regulations |
| Global | Kyoto Protocol (GHG reduction), Montreal Protocol (ozone), Paris Agreement |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Confusing ozone layer depletion with global warming | Ozone depletion is caused by CFCs; global warming is caused by GHGs |
| Thinking acid rain is caused only by CO₂ | CO₂ causes ocean acidification; SO₂ and NOₓ cause acid rain |
| Calling CFCs the main greenhouse gas | CFCs are potent GHGs but CO₂ is the most abundant |
| Mixing BOD and COD | BOD = biological oxygen demand (organic waste); COD = chemical oxygen demand |
ICSE Exam Focus
This chapter carries 4–6 marks. Key topics: air/water/soil/noise pollution (causes, effects, control), global warming, ozone depletion, acid rain.
Marks Blueprint: Types of pollution — 3 marks, Global issues — 3 marks.
Self-Test Questions
-
List four major air pollutants and their sources.
-
What is eutrophication? Explain its process and consequences.
-
Differentiate between global warming and ozone depletion.
-
What is acid rain? How is it formed and what are its effects?
-
List three control measures for (a) air pollution, (b) water pollution.
-
What are greenhouse gases? How does the enhanced greenhouse effect lead to global warming?
