Unit 4: Environmental pollution

Environmental pollution is the introduction of contaminants into the natural environment at rates faster than they can be dispersed, diluted, decomposed or stored, causing adverse change. Pollutants may be biodegradable (sewage, food waste) or non-degradable (DDT, plastics, heavy metals).

• Pollutant: any substance or energy released above threshold levels — CO, SO₂, Pb, noise (dB), or radiation (Sv).
• Point vs non-point source: a chimney or effluent pipe (point) versus agricultural runoff or urban traffic (non-point).
• Primary vs secondary: emitted directly (SO₂, NO) versus formed in situ (ozone, PAN, H₂SO₄).
• Major causes: industrialisation, fossil-fuel combustion, deforestation, agrochemical use, urbanisation and rising per-capita consumption.
• Types by medium: air, water, soil, noise, radiation and thermal pollution.

II. Air Pollution

Contamination of the atmosphere by gases and particulates.

A. Effects

• Human health: SO₂ and NOₓ cause bronchitis and asthma; CO binds haemoglobin (forming carboxyhaemoglobin) reducing O₂ transport; PM₂.₅ penetrates alveoli causing cardiopulmonary disease.
• Environmental: photochemical smog (NOₓ + hydrocarbons + sunlight → ozone, PAN); reduced visibility; damage to chlorophyll and stomata in plants.
• Materials: corrosion of metals and marble (the "stone leprosy" on the Taj Mahal from SO₂).

B. Controls

• Source control: cleaner fuels (CNG, LPG), desulphurised coal.
• Devices: electrostatic precipitators and bag filters remove particulates; scrubbers absorb SO₂; catalytic converters oxidise CO and hydrocarbons in vehicles.
• Legislation: ambient air-quality standards, tall stacks for dispersion, green belts.

III. Water Pollution

Degradation of water quality making it unfit for use.

A. Effects

• Oxygen depletion: organic waste raises BOD; high BOD lowers dissolved oxygen, killing fish.
• Eutrophication: nitrate/phosphate runoff triggers algal blooms → decomposition → hypoxic dead zones.
• Toxicity & disease: heavy metals bioaccumulate; pathogens cause cholera, typhoid, dysentery.

B. Controls

• Treatment: primary (sedimentation), secondary (activated sludge, biological oxidation), tertiary (nutrient/chemical removal).
• Prevention: effluent standards, restricting phosphate detergents, riparian buffer strips, watershed protection.

IV. Soil Pollution

Introduction of harmful substances degrading soil fertility and structure.

A. Effects

• Fertility loss: excess fertiliser causes salinisation and alters pH; pesticides kill soil microflora and earthworms.
• Contamination transfer: heavy metals and persistent organics enter crops and the food chain.
• Land degradation: waterlogging and hardpan formation reduce arable value.

B. Controls

• Practices: integrated pest management, organic manure, crop rotation, biofertilisers.
• Remediation: bioremediation using microbes, phytoremediation using hyperaccumulator plants, controlled landfill lining.

V. Noise Pollution

Unwanted sound exceeding tolerance limits, measured in decibels (dB).

A. Effects

• Auditory: prolonged exposure above 85 dB causes hearing loss; a threshold of pain near 120 dB.
• Non-auditory: hypertension, sleep disturbance, reduced concentration, elevated stress hormones.

B. Controls

• Source reduction: silencers, engine mufflers, insulated machinery.
• Path & receiver: sound barriers, green belts, acoustic enclosures, ear muffs; zoning of industries and silence zones near hospitals and schools.

VI. Radiation Pollution

Release of ionising radiation into the environment.

A. Effects

• Natural vs anthropogenic sources: cosmic rays and radon versus nuclear tests, reactors, X-rays.
• Biological damage: ionising radiation breaks DNA, causing mutations, cancer (leukaemia), and radiation sickness; measured in sieverts (Sv).

B. Controls

• Shielding & containment: lead/concrete barriers, sealed reactor cores, controlled disposal of radioactive waste in deep geological repositories.
• Regulation: exposure limits, monitoring badges, restricted zones around installations.

VII. Emerging Pollutants

Newly recognised contaminants not yet routinely regulated.

• Pharmaceuticals & personal-care products: antibiotics and hormones in water bodies promote resistance and endocrine disruption.
• Microplastics: fragments below 5 mm ingested by aquatic organisms, entering the food chain.
• Nanomaterials and PFAS: persistent "forever chemicals" resistant to degradation, bioaccumulative and difficult to treat.

VIII. Fireworks and Their Ill-Effects

Combustion of pyrotechnic mixtures releasing pollutants and noise.

• Air quality: sharp spikes in PM₂.₅ and PM₁₀; release of SO₂, NOₓ and metallic oxides (barium green, strontium red, copper blue).
• Noise: bursts of 125–150 dB harming hearing and distressing animals.
• Other harms: solid debris litter, fire and burn injuries, respiratory aggravation in asthmatics.

IX. Global Warming

Rise in average surface temperature from enhanced greenhouse effect.

• Mechanism: greenhouse gases (CO₂, CH₄, N₂O, CFCs) trap outgoing infrared radiation.

Incoming solar (short-wave) → surface absorption
→ re-emitted long-wave IR → absorbed by GHGs → re-radiated back

• Drivers: fossil-fuel combustion, deforestation, livestock (methane).
• Consequences: melting ice caps, sea-level rise, shifting monsoons.
• Mitigation: renewable energy, afforestation, carbon capture, efficiency standards.

X. Climate Change

Long-term alteration of temperature and weather patterns.

• Manifestations: erratic rainfall, more frequent droughts, floods and intense cyclones.
• Ecosystem shifts: altered species ranges, coral bleaching, glacial retreat.
• Response frameworks: adaptation (resilient crops, flood defences) and mitigation (emission cuts under international accords).

XI. Ozone Layer Depletion

Thinning of stratospheric ozone that shields UV radiation.

• Cause: chlorine from CFCs catalytically destroys ozone.

CFC + UV → Cl•
Cl• + O₃ → ClO + O₂
ClO + O → Cl• + O₂   (Cl regenerated → chain reaction)

• Ozone hole: severe seasonal loss over Antarctica.
• Effects: increased UV-B causing skin cancer, cataracts, immune suppression and crop damage.
• Control: phase-out of CFCs and halons; substitution with HFCs.

XII. Acid Rain

Precipitation with pH below 5.6 from atmospheric acids.

• Formation: SO₂ and NOₓ oxidise and dissolve in moisture.

SO₂ + ½O₂ + H₂O → H₂SO₄
2NO₂ + H₂O → HNO₃ + HNO₂

• Effects: acidification of lakes killing aquatic life; leaching of soil nutrients; corrosion of buildings and forest dieback.
• Control: flue-gas desulphurisation, low-sulphur fuels, liming of acidified lakes.

XIII. Impacts on Human Communities and Agriculture

Social and food-security consequences of pollution and climate stress.

A. Human communities

• Health burden: rising respiratory and waterborne diseases; heat-stress mortality.
• Displacement: sea-level rise and disasters create climate refugees; loss of livelihoods.

B. Agriculture

• Yield loss: ozone and heat reduce photosynthesis; altered rainfall disrupts sowing.
• Soil & water stress: salinisation, groundwater depletion and pest range shifts threaten food security.

XIV. Case Studies on Pollution

Documented incidents illustrating pollution impacts.

• Bhopal gas tragedy (1984): leak of methyl isocyanate (MIC) from a pesticide plant killed thousands — a benchmark industrial-air disaster.
• Minamata disease (Japan): methylmercury discharge into Minamata Bay caused neurological damage through fish consumption.
• Chernobyl (1986): reactor explosion released radioactive material over Europe, illustrating long-term radiation pollution.

XV. Solid Waste Management

Systematic handling of discarded materials.

• Waste streams: municipal, industrial, biomedical, e-waste, hazardous.
• Hierarchy — the 4 Rs: Reduce, Reuse, Recycle, Recover, before final disposal.
• Processing methods:
  • Composting/vermicomposting: biodegradable waste converted to manure.
  • Incineration: volume reduction with energy recovery; requires flue-gas control.
  • Sanitary landfill: lined, capped sites with leachate collection and methane venting.
  • Segregation: source separation of wet, dry and hazardous fractions.

XVI. Control Measures of Urban and Industrial Waste

Managing high-volume waste from cities and industries.

A. Urban waste

• Collection & segregation: door-to-door collection, colour-coded bins, decentralised composting.
• Sewage: treatment plants before discharge; recycling treated water for irrigation.

B. Industrial waste

• Cleaner production: process modification to minimise waste at source; recovery of by-products.
• Effluent & emission treatment: ETPs, scrubbers and precipitators before release.
• Hazardous handling: secure landfills, deep-well injection under regulation, and adherence to statutory discharge standards with continuous monitoring.