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 harm to living organisms and ecosystems.

Defining properties (referred to throughout):

• Pollutant: any substance or energy (chemical, biological, physical) present in excess of natural levels.
• Point vs non-point source: a single identifiable outlet (factory pipe) versus diffuse origins (farm runoff).
• Degradable vs non-degradable: sewage and food waste break down; plastics, DDT and heavy metals persist and bioaccumulate.
• Primary vs secondary: emitted directly (SO₂, CO) versus formed in the environment (ozone, PANs, acid rain).
• Types: air, water, soil, noise, radiation, thermal and marine pollution.
• Causes: industrialisation, fossil-fuel combustion, urbanisation, agriculture (fertilisers, pesticides), deforestation and unmanaged waste.

II. Air Pollution — contaminants of the atmosphere

Air pollution is the presence of gases and particulates in concentrations that harm health, materials and climate.

A. Effects

• Human health: SPM and PM₂.₅ cause bronchitis and lung cancer; CO binds haemoglobin (carboxyhaemoglobin) starving tissues of O₂.
• Vegetation: SO₂ causes chlorosis and necrosis of leaves; fluorides damage crops.
• Materials and climate: SO₂ and NOₓ corrode marble (Taj Mahal disease); greenhouse gases warm the planet.

B. Controls

• Source control: cleaner fuels (CNG), low-sulphur coal, catalytic converters.
• Equipment: electrostatic precipitators (remove ~99% particulates), cyclone separators, bag filters, wet scrubbers for gases.
• Dispersion and law: tall stacks; National Ambient Air Quality Standards.

III. Water Pollution — degradation of water bodies

Water pollution is contamination of surface or ground water by sewage, industrial effluent, agricultural runoff and pathogens.

A. Effects

• Oxygen depletion: organic waste raises BOD; decomposition depletes dissolved oxygen, killing fish.
• Eutrophication: nitrates and phosphates trigger algal blooms, then oxygen crash.
• Health: pathogens cause cholera and typhoid; nitrates cause blue-baby syndrome; arsenic and fluoride poisoning of groundwater.
• Bioaccumulation: mercury and DDT concentrate up the food chain.

B. Controls

• Treatment: primary (screening, sedimentation), secondary (activated sludge, biological oxidation), tertiary (nutrient and chemical removal).
• Prevention: effluent treatment plants before discharge; buffer strips to cut runoff; ban on untreated dumping.

IV. Soil Pollution — degradation of the land resource

Soil pollution is the build-up of toxic chemicals, salts and waste that reduces soil fertility and productivity.

A. Effects

• Fertility loss: excess fertilisers and pesticides kill soil microbes; salinisation from over-irrigation.
• Contamination: heavy metals and plastics enter crops and groundwater.
• Health: toxic residues reach humans through the food chain.

B. Controls

• Practice: integrated pest management, biofertilisers, crop rotation, controlled fertiliser use.
• Remediation: bioremediation, phytoremediation, proper landfill lining, reduced plastic use.

V. Noise Pollution — unwanted sound as a pollutant

Noise pollution is exposure to sound levels (measured in decibels, dB) high enough to harm health; safe ambient limit is around 45–65 dB.

A. Effects

• Physiological: hearing loss above ~85 dB prolonged; raised blood pressure, sleeplessness.
• Psychological: stress, irritability, reduced concentration.
• Sources: traffic, industry, loudspeakers, aircraft, fireworks.

B. Controls

• Source: silencers on vehicles, quieter machinery, restricted horn use.
• Path and receiver: green belts and sound barriers, acoustic insulation, ear protectors; silence zones near hospitals and schools.

VI. Radiation Pollution — hazards of ionising energy

Radiation pollution is release of radioactive material or ionising radiation (alpha, beta, gamma, X-rays) into the environment.

A. Effects

• Somatic: radiation burns, radiation sickness, cancers (leukaemia).
• Genetic: mutations passed to offspring; long half-life isotopes (Sr-90, Cs-137, I-131) persist.
• Sources: natural (radon, cosmic), man-made (nuclear tests, reactor accidents, medical X-rays, mining).

B. Controls

• Containment: shielding (lead, concrete), safe reactor design, sealed disposal of waste.
• Monitoring: dose limits, protective gear, siting plants away from population.

VII. Emerging Pollutants — newly recognised contaminants

Emerging pollutants are synthetic or naturally occurring chemicals, unregulated until recently, detected at trace levels with poorly understood effects.

• Categories: pharmaceuticals and antibiotics, personal-care products, microplastics, endocrine disruptors, flame retardants, per- and polyfluoroalkyl substances (PFAS).
• Concern: persistence, antibiotic resistance, hormonal disruption in aquatic life; conventional treatment plants do not remove them.
• Control: advanced oxidation, activated carbon and membrane filtration, take-back schemes for drugs.

VIII. Fireworks and Their Ill-Effects

Fireworks release a short, intense burst of air and noise pollution from combustion of metal salts and oxidisers.

• Air: sharp spikes in PM₂.₅, SO₂ and toxic metals (barium green, copper blue, strontium red).
• Noise: bursts exceeding 125 dB harm hearing.
• Other: burn injuries, litter, animal distress; residues contaminate soil and water.
• Control: green crackers, community displays, time and decibel limits.

IX. Global Warming — rise in mean surface temperature

Global warming is the gradual increase in Earth's average temperature due to the enhanced greenhouse effect.

• Mechanism: CO₂, CH₄, N₂O and CFCs trap outgoing infrared radiation.

Incoming solar (shortwave) → absorbed by Earth →
re-emitted as longwave IR → trapped by greenhouse gases → warming

• Causes: fossil-fuel burning, deforestation, industry, livestock (methane).
• Effects: melting glaciers, sea-level rise, extreme weather.
• Control: renewable energy, afforestation, carbon capture, emission treaties (Kyoto, Paris).

X. Climate Change — long-term shifts in climate patterns

Climate change is the sustained alteration of temperature, rainfall and weather patterns driven largely by global warming.

• Manifestations: erratic monsoons, droughts, floods, cyclones of greater intensity.
• Ecological: shifting species ranges, coral bleaching, disrupted breeding cycles.
• Mitigation vs adaptation:
  1. Mitigation: cut emissions at source.
  2. Adaptation: flood defences, drought-resistant crops, early-warning systems.

XI. Ozone Layer Depletion — thinning of stratospheric ozone

Ozone (O₃) in the stratosphere absorbs harmful UV-B; its depletion by halogens forms seasonal "holes", notably over Antarctica.

• Mechanism: UV splits CFCs, releasing chlorine that destroys ozone catalytically.

CFCl₃ + UV → Cl• + products
Cl• + O₃ → ClO• + O₂
ClO• + O → Cl• + O₂   (Cl regenerated, one atom destroys ~100,000 O₃)

• Effects: more UV-B reaching surface causes skin cancer, cataracts, reduced crop yield.
• Control: Montreal Protocol (1987) phasing out CFCs; HFC and HCFC substitutes.

XII. Acid Rain — precipitation acidified by oxides

Acid rain is rainfall with pH below 5.6 caused by atmospheric SO₂ and NOₓ dissolving into acids.

• Chemistry: SO₂ → H₂SO₄; NOₓ → HNO₃.

SO₂ + H₂O → H₂SO₃ ;  2SO₂ + O₂ → 2SO₃ ;  SO₃ + H₂O → H₂SO₄

• Effects: acidifies lakes killing fish, leaches soil nutrients and aluminium, damages forests, corrodes buildings.
• Control: flue-gas desulphurisation, low-sulphur fuels, liming of affected lakes.

XIII. Impacts on Human Communities and Agriculture

Pollution and climate stress fall unevenly, hitting the poor and food systems hardest.

• Communities: respiratory and waterborne disease, displacement of coastal and low-lying populations (climate refugees), livelihood loss for fishers and farmers.
• Agriculture: ozone and SO₂ cut yields; soil salinisation and erosion; erratic rainfall and heat reduce productivity; pest ranges expand.
• Equity: marginalised groups face highest exposure and least capacity to adapt.

XIV. Case Studies on Pollution

Landmark disasters illustrate causes, effects and the need for regulation.

• Bhopal Gas Tragedy (1984): leak of methyl isocyanate (MIC) from Union Carbide killed thousands; taught industrial safety and liability.
• Minamata Disease (Japan, 1950s): methylmercury effluent bioaccumulated in fish, causing neurological damage.
• Chernobyl (1986): reactor explosion spread radioactive fallout across Europe.
• Ganga pollution: sewage and industrial effluent prompted the Namami Gange programme.

XV. Solid Waste Management — handling of solid refuse

Solid waste management is the systematic control of generation, collection, treatment and disposal of solid waste.

• Types: municipal (domestic), industrial, biomedical, e-waste, hazardous.
• Hierarchy: reduce, reuse, recycle, recover, then dispose.
• Methods:
  1. Composting/vermicomposting: biodegradable waste converted to manure.
  2. Incineration: burning to cut volume and recover energy, with emission control.
• Disposal: sanitary landfills with liners and leachate collection; source segregation into wet and dry.

XVI. Control Measures of Urban and Industrial Waste

Urban and industrial waste require targeted treatment before release to protect land, air and water.

• Urban: segregation at source, door-to-door collection, sewage treatment plants, biogas from organic waste, banning open dumping and burning.
• Industrial: effluent treatment plants and scrubbers, cleaner production and process modification, resource recovery and recycling of by-products.
• Regulation and principle: the polluter-pays and precautionary principles, common effluent treatment plants for clusters, and strict enforcement of pollution-control-board standards.