Unit 4: Environmental pollution

I. Definition: the framework of environmental pollution

Environmental pollution is the introduction of energy or substances into air, water or land at rates exceeding the environment's capacity to disperse, dilute, degrade or absorb them, producing harm to living organisms, property or amenity. The concept is codified in India by the Environment (Protection) Act, 1986, which defines an "environmental pollutant" as any solid, liquid or gaseous substance present in such concentration as may be, or tend to be, injurious to the environment.

• Pollutant vs. contaminant: a contaminant is any substance not naturally present; it becomes a pollutant only when its concentration crosses a threshold causing harm (e.g. fluoride is essential at 0.5 mg/L, toxic above 1.5 mg/L in drinking water).
• Primary vs. secondary: primary pollutants are emitted directly (SO₂, CO, PM); secondary form in the environment by reaction (ozone, PAN, H₂SO₄ in acid rain).
• Point vs. non-point sources: an identifiable outfall or stack (a chimney, a sewer pipe) versus diffuse sources (agricultural runoff, urban stormwater).
• Degradable vs. non-degradable: sewage and paper break down; DDT, plastics and heavy metals persist and undergo bioaccumulation (build-up in one organism) and biomagnification (rising concentration up trophic levels — DDT magnified ~10⁵ times from water to fish-eating birds).
• Standards: regulation works through ambient standards (NAAQS) and emission/effluent standards enforced by the CPCB and State Pollution Control Boards.

II. Air pollution — the atmospheric medium

Air pollution is the presence of gases, particulates or biological materials in the atmosphere in concentrations harmful to humans, other life or materials.

A. Types and causes

• Particulates: PM₁₀ and PM₂.₅ from combustion, construction dust, stubble burning; PM₂.₅ penetrates alveoli.
• Gaseous: SO₂ (coal burning, smelting), NOₓ (high-temperature combustion, vehicles), CO (incomplete combustion), hydrocarbons, NH₃ (agriculture).
• Secondary/photochemical: ground-level O₃ and PAN formed from NOₓ + VOCs in sunlight — Los Angeles-type smog; London smog is the reducing SO₂–fog type.
• Indoor air pollution: biomass chulha smoke, radon, formaldehyde; a major cause of respiratory disease in rural India.

B. Effects

• Human health: bronchitis, asthma, COPD, lung cancer; CO binds haemoglobin ~210 times more strongly than O₂, forming carboxyhaemoglobin.
• Vegetation: SO₂ causes chlorosis and necrosis; O₃ causes stipple and yield loss in wheat and rice.
• Materials and visibility: stone decay, metal corrosion, haze reducing visibility.

C. Controls

• Particulate control devices: cyclone separators (coarse), bag filters, wet scrubbers, electrostatic precipitators (up to ~99% efficiency).
• Gaseous control: flue-gas desulphurisation (lime scrubbing: SO₂ + CaCO₃ + ½O₂ → CaSO₄ + CO₂), catalytic converters, low-sulphur BS-VI fuel.
• Regulatory: NAAQS (PM₂.₅ annual limit 40 µg/m³, 24-hour 60 µg/m³), tall stacks for dispersion, greenbelts, CNG conversion, AQI-based Graded Response Action Plan.

III. Water pollution — surface and groundwater

Water pollution is any alteration of physical, chemical or biological water quality that makes it unfit for its designated use.

A. Types and causes

• Organic/sewage: domestic wastewater raising BOD; high BOD depletes dissolved oxygen (fish need DO > 4–5 mg/L).
• Nutrients: nitrates and phosphates from fertiliser and detergents cause eutrophication — algal blooms, oxygen sag, fish kill.
• Toxic and industrial: heavy metals (Hg, Cd, Pb, As, Cr), tannery and dyeing effluent, pesticides.
• Thermal, radioactive and marine: power-plant coolant discharge lowering DO; oil spills forming films that block gas exchange.
• Groundwater: geogenic arsenic (West Bengal–Bangladesh) and fluoride (Rajasthan, Andhra); leachate from landfills.

B. Effects

• Waterborne disease: cholera, typhoid, hepatitis A, diarrhoea.
• Chronic toxicity: methylmercury → Minamata disease; cadmium → itai-itai; arsenic → keratosis and skin cancer; fluoride > 1.5 mg/L → dental and skeletal fluorosis.
• Ecosystem: hypoxic "dead zones", loss of biodiversity, biomagnification in food chains.

C. Controls

• Treatment train: primary (screening, sedimentation) → secondary (activated sludge, trickling filter, UASB reactors) → tertiary (filtration, chlorination, membrane).
• Source measures: effluent standards and zero-liquid-discharge for red-category industry, common effluent treatment plants for clusters, buffer strips against runoff.
• Statutory: Water (Prevention and Control of Pollution) Act, 1974; drinking-water specification IS 10500.

IV. Soil pollution — the terrestrial medium

Soil pollution is the accumulation of xenobiotic chemicals or waste in soil that degrades fertility and enters the food chain.

A. Types and causes

• Agrochemical: persistent pesticides (DDT, endosulfan), excess urea causing nitrate leaching and soil acidification.
• Industrial and mining: fly ash, tailings, heavy metals, e-waste acid leaching.
• Waste-derived: unlined dumpsites, sewage-sludge irrigation, plastic mulch residues.
• Salinisation/waterlogging: poor drainage in canal-irrigated tracts bringing salts to the surface.

B. Effects

• Productivity loss: reduced humus, disrupted N-fixing microflora, lower crop yield.
• Food-chain transfer: cadmium and lead uptake by leafy vegetables; groundwater contamination via leaching.
• Physical: loss of soil structure, erosion, desertification.

C. Controls

• Remediation: bioremediation, phytoremediation (Brassica juncea for lead; ferns for arsenic), soil washing, capping and containment.
• Preventive: integrated pest management, biofertilisers, crop rotation, composting of organic waste, lined landfills, contour bunding.

V. Noise pollution — unwanted sound

Noise pollution is unwanted or excessive sound measured in decibels on the A-weighted scale, dB(A), a logarithmic unit: a 10 dB rise is a tenfold rise in intensity.

A. Types and causes

• Sources: transport (traffic 70–90 dB, aircraft 120 dB), industrial machinery, construction, loudspeakers, DJ systems and generators.

B. Effects

• Auditory: temporary threshold shift; permanent hearing loss above ~85 dB for prolonged exposure; pain threshold ~120–130 dB.
• Non-auditory: hypertension, sleep disturbance, elevated cortisol, reduced work efficiency and learning in children.

C. Controls

• At source: silencers, mufflers, machine mounting on vibration dampers, low-noise equipment.
• In path: acoustic barriers, greenbelts, sound-insulated enclosures.
• Legal: Noise Pollution (Regulation and Control) Rules, 2000 — residential limits 55 dB(A) day / 45 dB(A) night; silence zones 50/40; day defined as 6 a.m.–10 p.m.

VI. Radiation pollution — ionizing and non-ionizing energy

Radiation pollution is the release of radiation into the environment above natural background levels, measured as absorbed dose in gray (Gy) and equivalent dose in sievert (Sv); natural background is about 2.4 mSv per year.

A. Types and causes

• Natural: cosmic rays, terrestrial ²³⁸U and ²³²Th series, radon-222 accumulating indoors.
• Anthropogenic: nuclear weapon tests, reactor accidents (¹³¹I, ¹³⁷Cs, ⁹⁰Sr), mining and milling of uranium, medical X-rays and radiotherapy, radioactive waste.
• Non-ionizing: UV, microwave, RF from transmission towers.

B. Effects

• Somatic: acute radiation sickness above ~1 Gy; erythema, sterility, cataract; leukaemia and thyroid cancer (⁹⁰Sr mimics calcium and lodges in bone).
• Genetic: chromosomal aberrations and mutations transmitted to progeny; no threshold assumed for stochastic effects.

C. Controls

• ALARA principle: dose minimised by time, distance and shielding (lead, concrete, water); occupational limit 20 mSv/year averaged over five years.
• Waste management: vitrification of high-level waste, deep geological disposal, dilution and delay for low-level waste, containment structures around reactors.

VII. Emerging pollutants

Substances not routinely monitored but increasingly detected in the environment with suspected ecological or health effects, also called contaminants of emerging concern.

• Pharmaceuticals and personal care products: antibiotics and analgesics in sewage; diclofenac caused ~99% decline in Indian Gyps vultures, prompting the 2006 veterinary ban.
• Microplastics: fragments < 5 mm from textiles, tyre wear and plastic breakdown; ingested by plankton and fish, vectors for adsorbed POPs.
• Endocrine-disrupting chemicals: bisphenol-A, phthalates, alkylphenols — interfere with hormone signalling, causing feminisation of fish.
• PFAS: per- and polyfluoroalkyl "forever chemicals" from non-stick and firefighting foam; extreme persistence.
• Antimicrobial resistance genes and nanomaterials: spread through hospital and pharmaceutical effluent; conventional STPs do not remove them, requiring advanced oxidation or activated carbon.

VIII. Fireworks and their ill-effects

Fireworks combine an oxidiser (potassium nitrate, perchlorate), fuel (charcoal, sulphur, aluminium) and metal salts for colour — strontium (red), barium (green), copper (blue), sodium (yellow).

• Air quality: PM₂.₅ spikes of 4–10 times ambient levels on Diwali night in Delhi, with SO₂, NO₂ and airborne Ba, Sr, Cu, Pb.
• Health: asthma and COPD exacerbation, eye and skin burns; perchlorate disrupts thyroid iodine uptake.
• Noise: crackers exceed 125 dB, breaching the 125 dB(AI) limit at 4 m; distress to infants, patients, birds and pets.
• Waste and social cost: unswept debris and heavy-metal residue in stormwater; child labour and factory explosions in manufacture.
• Control: CSIR-NEERI "green crackers" (SWAS, STAR, SAFAL) with ~30% lower particulate emission, restricted two-hour bursting windows, and community displays in place of individual use.

IX. Global environmental issues

A. Global warming

• Mechanism: greenhouse gases absorb outgoing infrared radiation; CO₂ has risen from ~280 ppm pre-industrial to over 420 ppm.
• Gases and GWP (100-yr): CO₂ = 1, CH₄ ≈ 28, N₂O ≈ 265, CFCs and SF₆ in the thousands.
• Observed change: global mean surface temperature is about 1.1–1.2 °C above the 1850–1900 baseline.

B. Climate change

• Manifestations: sea-level rise from thermal expansion and ice melt, glacial retreat in the Himalaya, erratic monsoon, intensified cyclones, heat waves.
• Impacts: crop yield decline (wheat is sensitive to terminal heat), vector-borne disease range expansion, climate refugees from Sundarbans and low-lying islands.
• Response: UNFCCC (1992), Kyoto Protocol (1997), Paris Agreement (2015) targeting "well below 2 °C"; India's NAPCC with eight missions.

C. Ozone layer depletion

• Chemistry: CFCs photolyse in the stratosphere releasing Cl, which catalytically destroys ozone.

CFCl₃ + UV → CFCl₂ + Cl·
Cl· + O₃ → ClO + O₂
ClO + O· → Cl· + O₂      (Cl· regenerated; ~10⁵ O₃ destroyed per Cl atom)

• Ozone hole: Antarctic springtime thinning below 220 Dobson Units, aided by polar stratospheric clouds.
• Effects and control: increased UV-B causing skin cancer, cataract and phytoplankton damage; the Montreal Protocol (1987) phased out CFCs and halons, with the Kigali Amendment (2016) covering HFCs.

D. Acid rain and impacts on human communities and agriculture

• Formation: natural rain has pH ≈ 5.6 (dissolved CO₂); acid rain is pH < 5.6, from SO₂ → H₂SO₄ and NOₓ → HNO₃ oxidation in cloud water.
• Agriculture and soil: leaching of Ca²⁺, Mg²⁺ and K⁺, mobilisation of toxic Al³⁺ that damages root hairs, inhibition of nitrogen-fixing bacteria, reduced yields.
• Aquatic: lake acidification below pH 5 eliminates fish eggs and molluscs.
• Human communities: corrosion of buildings and monuments — marble decay of the Taj Mahal led to the Taj Trapezium Zone directives (1996); respiratory irritation from sulphate aerosols; drinking-water contamination from leached lead and copper pipes.

X. Case studies on pollution

• Bhopal Gas Tragedy (2–3 December 1984): ~40 tonnes of methyl isocyanate leaked from the Union Carbide plant; thousands died within days, with lasting blindness, lung fibrosis and birth defects — the archetype of industrial safety failure.
• Minamata, Japan (disclosed 1956): methylmercury discharged by the Chisso factory biomagnified in fish, causing ataxia, sensory loss and congenital Minamata disease.
• Chernobyl (26 April 1986) and Fukushima Daiichi (11 March 2011): reactor accidents releasing ¹³¹I and ¹³⁷Cs, permanent exclusion zones and elevated thyroid cancer.
• Ganga pollution: tanneries at Kanpur, sewage from riverside towns; addressed by the Ganga Action Plan (1986) and Namami Gange (2014).
• Delhi winter smog: vehicular exhaust plus paddy stubble burning in Punjab and Haryana with temperature inversion pushing AQI into the "severe" band.

XI. Solid waste management — control measures of urban and industrial waste

Solid waste management is the systematic collection, transport, processing and disposal of waste, governed in India by the Solid Waste Management Rules, 2016.

A. Control measures of urban waste

• Composition and quantum: Indian cities generate roughly 0.4–0.6 kg per capita per day, ~50% biodegradable, 30% inert, 20% recyclable.
• Segregation at source: mandatory three-bin separation into wet (green), dry (blue) and domestic hazardous (black) streams.
• Processing: aerobic composting and vermicomposting of wet waste; biomethanation yielding biogas; refuse-derived fuel pellets; waste-to-energy incineration with flue-gas cleaning.
• Disposal: sanitary landfill only for inert residue — clay/HDPE liner, leachate collection and treatment, landfill-gas venting, daily soil cover, final capping and post-closure monit