39 Environmental Issues and Pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Six recognised types are commonly examined: air, water, soil, noise, thermal, and radiation pollution. Newer categories — light, plastic, and electronic-waste pollution — have grown in policy importance.
39.1 Air Pollution
Air pollution arises from gases, particulates and biological substances released into the atmosphere.
| Pollutant | Main source | Health/environment effect |
|---|---|---|
| PM10, PM2.5 (Particulate Matter) | Combustion, dust, vehicles | Respiratory and cardiovascular disease |
| SO₂ (Sulphur dioxide) | Coal-fired plants, smelters | Acid rain, respiratory irritation |
| NOₓ (NO, NO₂) | Vehicle exhaust, power plants | Smog, acid rain |
| CO (Carbon monoxide) | Incomplete combustion | Reduces blood oxygen carrying |
| O₃ (Ground-level ozone) | NOₓ + VOCs + sunlight | Respiratory disease; crop damage |
| VOCs (Volatile Organic Compounds) | Solvents, paints, vehicles | Photochemical smog |
| CO₂ | Fossil fuel combustion | Climate change |
| CH₄ (Methane) | Livestock, paddies, landfills | Potent GHG |
| CFCs | Old refrigerants, aerosols | Ozone depletion |
| Lead | Older fuels, paint, batteries | Neurotoxic |
- Classical / London-type smog (sulphurous) — coal burning + cold humid air → SO₂ + soot.
- Photochemical / Los-Angeles smog — vehicle exhaust + sunlight → ground-level ozone, PAN, NO₂.
Indian cities (Delhi NCR, especially in winter) experience a mixed smog with both types.
39.2 Water Pollution
| Pollutant | Source | Effect |
|---|---|---|
| Pathogens | Untreated sewage | Cholera, typhoid, hepatitis |
| Heavy metals | Industrial effluent, mining | Mercury, lead, arsenic, cadmium toxicity |
| Pesticides / Fertilisers | Agricultural runoff | Eutrophication, biomagnification |
| Industrial chemicals | Factories, dyeing, tanning | Toxicity, cancer |
| Oil spills | Tankers, drilling | Marine biodiversity damage |
| Microplastics | Plastic breakdown | Ingested by marine life; reaches food chain |
| Thermal pollution | Power plants discharging hot water | Reduced dissolved oxygen |
Eutrophication is the over-enrichment of a water body with nutrients (nitrogen, phosphorus). Steps:
- Fertiliser/sewage runoff adds N and P.
- Algae bloom on surface.
- Algae die and bacteria decompose them.
- Decomposition consumes oxygen.
- Fish and aquatic life suffocate.
Result: a dead zone with very low dissolved oxygen.
39.3 Soil Pollution
| Pollutant | Source | Effect |
|---|---|---|
| Pesticides, herbicides | Agriculture | Persistence, biomagnification |
| Industrial waste | Factories | Heavy-metal contamination |
| E-waste | Discarded electronics | Lead, cadmium, mercury leaching |
| Plastic | Packaging | Slow degradation |
| Salinity | Over-irrigation | Reduced crop productivity |
39.4 Noise Pollution
Noise is unwanted sound. Indian standards (Noise Pollution (Regulation and Control) Rules, 2000) prescribe maximum levels by zone.
| Zone | Day (6 am – 10 pm) | Night (10 pm – 6 am) |
|---|---|---|
| Industrial | 75 | 70 |
| Commercial | 65 | 55 |
| Residential | 55 | 45 |
| Silence (near hospitals, schools) | 50 | 40 |
Effects: hearing damage (above 85 dB sustained), stress, sleep disturbance, hypertension.
39.5 Thermal Pollution
Thermal pollution is the unwanted heating of water bodies, primarily from power-plant cooling water. Effects: lower dissolved oxygen, disrupted aquatic life cycles, algal blooms.
39.6 Plastic Pollution
Plastic accumulates in landfills, oceans (Pacific Garbage Patch) and food chains as microplastics. India banned single-use plastics from 1 July 2022 (Plastic Waste Management Rules amendments).
39.7 E-Waste
Electronic waste — discarded computers, phones, batteries — contains heavy metals (lead, mercury, cadmium) and is regulated in India by E-Waste (Management) Rules, 2022.
39.8 Climate Change Issues
- Global warming — rising global mean temperature, primarily from CO₂, CH₄, N₂O, fluorinated gases.
- Ozone depletion — thinning of stratospheric ozone by CFCs; Antarctic ozone hole.
- Acid rain — SO₂ and NOₓ react with water to form H₂SO₄ and HNO₃; pH < 5.6.
| Gas | Source | Global Warming Potential (relative to CO₂, 100-yr) |
|---|---|---|
| Carbon dioxide (CO₂) | Fossil fuels, deforestation | 1 (reference) |
| Methane (CH₄) | Livestock, paddy, landfills, fossil-fuel leaks | ~28 |
| Nitrous oxide (N₂O) | Agriculture, fertilisers | ~265 |
| HFCs, PFCs, SF₆ | Refrigerants, industry | Hundreds to thousands |
39.9 Acid Rain
Acid rain is precipitation with pH < 5.6, formed when SO₂ and NOₓ react with atmospheric moisture.
Effects: damages forests, lakes, monuments (Taj Mahal corrosion), aquatic biodiversity.
39.10 Ozone Depletion
The stratospheric ozone layer (O₃) shields Earth from harmful UV radiation. CFCs and HCFCs released by old refrigerators, aerosols and air-conditioners catalyse ozone destruction. The Antarctic ozone hole was first observed in 1985.
Distinguish: ground-level ozone is a pollutant (in smog); stratospheric ozone is a protective shield.
39.11 Working Issues in India
- Delhi NCR air pollution — winter smog, stubble burning.
- Ganga river pollution — Namami Gange Programme.
- Yamuna foam and pollution — encroachment, sewage.
- Vehicular emissions — BS-VI norms since April 2020.
- Stubble burning in Punjab/Haryana.
- Industrial clusters — NOIDA, Vapi, Ankleshwar, Ludhiana.
- Solid waste management — Swachh Bharat Mission.
39.12 Practice Questions
In air-quality terminology, "PM2.5" refers to:
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Eutrophication of a lake is most directly caused by:
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Acid rain is mainly caused by atmospheric:
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Which of the following greenhouse gases has the *highest* Global Warming Potential per molecule (over 100 years)?
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Photochemical smog (Los Angeles type) is mainly produced by:
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Under India's Noise Pollution Rules, the maximum permissible day-time noise level in a "silence zone" near a hospital is:
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Stratospheric ozone is depleted primarily by:
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Single-use plastics were banned in India with effect from:
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- Six pollution types: Air, Water, Soil, Noise, Thermal, Radiation + plastic, light, e-waste.
- Air pollutants: PM2.5, PM10, SO₂, NOₓ, CO, O₃, CO₂, CH₄, CFCs, lead.
- Eutrophication = N+P → algal bloom → low DO → fish kill.
- Acid rain = SO₂ + NOₓ → H₂SO₄ + HNO₃; pH < 5.6.
- Photochemical smog = NOₓ + VOCs + sunlight → ground-level O₃.
- GHGs: CO₂ (1), CH₄ (~28), N₂O (~265), SF₆ (~23,500) GWP-100.
- Stratospheric ozone depleted by CFCs/HCFCs → Montreal Protocol 1987.
- India: single-use plastic ban 1 July 2022; BS-VI norms 2020; Noise Rules 2000.