Unit 4: Environmental pollution

I. Environmental pollution — orientation

Environmental pollution is the undesirable alteration of air, water, soil, or physical surroundings by substances or energy that harm organisms, ecosystems, property, or human welfare. Pollution may be natural, but modern pollution is mainly associated with industry, transport, agriculture, urbanisation, and intensive resource use.

• Pollutant: A chemical, biological agent, or form of energy present at a harmful concentration; examples include particulate matter, sewage bacteria, pesticides, and noise.
• Source–pathway–receptor relationship: A source releases pollution, an environmental pathway transports it, and a receptor experiences exposure or damage.
• Concentration and dose: Effects depend on amount, duration, route of exposure, and toxicity; inhaled dose is influenced by pollutant concentration and breathing rate.
• Prevention principle: Avoiding generation at source is generally more effective than treating pollution after release.
• Assimilative capacity: Air, water, and soil can absorb limited wastes through dilution, decomposition, or chemical transformation, but excessive loading causes degradation.

II. Environmental pollution — classification and origins

A. Definition, types and causes of environmental pollution

This topic establishes how pollution is identified and why it occurs.

• Types by medium: Air, water, soil, noise, and radiation pollution affect different environmental components.
• Types by origin: Natural sources include volcanic ash and forest fires; anthropogenic sources include vehicles, factories, mining, sewage, and farms.
• Types by formation: Primary pollutants, such as sulfur dioxide (SO₂), are emitted directly; secondary pollutants, such as ozone (O₃) in smog, form through atmospheric reactions.
• Major causes: Fossil-fuel combustion, untreated waste, excessive fertiliser and pesticide use, deforestation, population concentration, and weak environmental regulation.
• Persistence: Lead and mercury remain for long periods, whereas biodegradable organic matter can be decomposed by microorganisms.

III. Air pollution — atmospheric contamination

Air pollution occurs when gases, particles, or biological materials alter atmospheric composition and impair health or ecosystems.

A. Air pollution: effects and controls

The severity of air pollution depends on pollutant type, concentration, exposure time, and weather conditions.

• Major pollutants: PM₂.₅ and PM₁₀ penetrate the respiratory system; CO reduces oxygen transport; SO₂ and nitrogen oxides (NOₓ) irritate airways; ground-level O₃ damages lung tissue.
• Health effects: Fine particles are associated with asthma, bronchitis, cardiovascular disease, and premature mortality; CO poisoning may cause unconsciousness because it forms carboxyhaemoglobin.
• Environmental effects: SO₂ and NOₓ contribute to acid deposition; O₃ damages leaves and reduces crop yield; particles reduce visibility and settle on buildings.
• Control at source: Use renewable energy, public transport, low-sulfur fuel, energy-efficient equipment, and cleaner production.
• Engineering controls: Cyclones remove coarse particles; electrostatic precipitators charge and collect fine particles; fabric filters trap dust; scrubbers absorb gases such as SO₂.
• Regulatory monitoring: Ambient air-quality standards, emission permits, vehicle inspection, and continuous monitoring reduce exposure; planting trees helps but cannot replace emission control.

IV. Water pollution — degradation of aquatic systems

Water pollution is the introduction of substances or organisms that make surface water or groundwater unsafe or ecologically impaired.

A. Water pollution: effects and controls

Water quality is assessed through physical, chemical, and biological indicators such as dissolved oxygen (DO), biochemical oxygen demand (BOD), pH, turbidity, and coliform counts.

• Sources: Domestic sewage, industrial effluent, oil, mine drainage, fertiliser runoff, pesticides, plastics, and heated cooling water contaminate rivers, lakes, oceans, and aquifers.
• Oxygen depletion: Microbial decomposition of organic matter raises BOD and consumes DO; fish may die when DO becomes very low.
• Eutrophication: Excess nitrate and phosphate stimulate algal blooms; decomposition then creates oxygen-deficient “dead zones.”
• Health effects: Pathogens cause cholera, dysentery, and hepatitis; mercury and arsenic bioaccumulate in aquatic food chains.
• Controls: Sewage treatment uses screening, primary settling, biological treatment, and disinfection; industries should recover chemicals and treat effluent before discharge.
• Prevention: Riparian vegetation, reduced fertiliser use, stormwater control, rainwater harvesting, and strict discharge standards protect watersheds.

V. Soil pollution — contamination of land resources

Soil pollution is the accumulation of solid, liquid, or gaseous substances that reduce soil quality and harm organisms or food production.

A. Soil pollution: effects and controls

Because soil stores nutrients and supports crops, contamination may persist for decades and enter food chains.

• Sources: Excess fertilisers, pesticides, mining residues, landfill leachate, petroleum, plastics, electronic waste, and industrial metals such as lead, cadmium, and chromium.
• Effects on soil: Contaminants alter pH, salinity, microbial activity, structure, and fertility; pesticides may kill beneficial insects and decomposers.
• Food-chain transfer: Crops may absorb cadmium or lead; livestock and humans are exposed through contaminated food, dust, or groundwater.
• Controls: Integrated pest management, organic manure, soil testing, controlled irrigation, and reduced chemical application limit contamination.
• Remediation: Excavation, bioremediation by microorganisms, phytoremediation using plants, soil washing, and secure containment treat polluted sites.

VI. Noise pollution — unwanted sound

Noise pollution is excessive or unwanted sound that causes physiological, psychological, or social disturbance.

A. Noise pollution: effects and controls

Sound is measured in decibels (dB), with exposure risk increasing as intensity and duration rise.

• Sources: Road traffic, aircraft, construction, factories, loudspeakers, and fireworks produce continuous or impulsive noise.
• Human effects: Prolonged exposure can cause hearing loss, tinnitus, sleep disturbance, hypertension, stress, and reduced concentration; children may experience impaired learning.
• Ecological effects: Noise disrupts bird communication, breeding, migration, and predator–prey behaviour.
• Controls: Zoning, silencers, machine maintenance, acoustic enclosures, sound barriers, green belts, and restricted operating hours reduce noise.
• Personal protection: Earplugs and earmuffs reduce exposure, but source control is preferable; residential limits commonly distinguish daytime from nighttime noise.

VII. Radiation pollution — exposure to ionising energy

Radiation pollution is harmful exposure to ionising or excessive non-ionising radiation from natural or human activities.

A. Radiation pollution: effects and controls

Ionising radiation has enough energy to damage cellular molecules and DNA; exposure is controlled through time, distance, and shielding.

• Sources: Radon, medical X-rays, nuclear reactors, radioactive waste, uranium mining, and nuclear accidents are important sources.
• Effects: High doses cause burns and radiation sickness; long-term exposure increases cancer, genetic damage, cataracts, and developmental disorders.
• Controls: Apply the ALARA principle—exposure should be “as low as reasonably achievable”—using minimum time, maximum distance, and suitable shielding.
• Safety systems: Dosimeters, sealed sources, reactor containment, emergency plans, secure waste storage, and controlled disposal prevent releases.
• Non-ionising radiation: Excessive ultraviolet radiation damages skin and eyes; sunscreen, protective clothing, and reduced exposure provide control.

VIII. Emerging pollutants and fireworks

A. Emerging pollutants

Emerging pollutants are newly recognised or inadequately regulated contaminants detected at low concentrations but capable of significant effects.

• Examples: Pharmaceutical residues, antibiotics, hormones, endocrine-disrupting chemicals, microplastics, per- and polyfluoroalkyl substances (PFAS), and antibiotic-resistance genes.
• Pathways: They enter water through excretion, household products, industrial discharge, landfill leachate, and wastewater-treatment plants.
• Concern: Conventional treatment may not remove all trace chemicals; endocrine disruptors can affect reproduction even at very low concentrations.
• Controls: Product substitution, take-back schemes, advanced oxidation, activated carbon, membrane filtration, source monitoring, and precautionary regulation are required.

B. Fireworks and their ill-effects

Fireworks create short-term but intense releases of particulate matter, gases, noise, and metal compounds.

• Air contamination: Combustion produces PM₂.₅, sulfur compounds, nitrogen oxides, and metal particles; strontium, barium, copper, and aluminium create colours.
• Health effects: Smoke aggravates asthma and cardiovascular disease; loud explosions cause hearing stress, anxiety, and disturbance to infants and animals.
• Other impacts: Firework debris contaminates soil and water, while sparks can ignite fires and cause burns.
• Controls: Community displays, time restrictions, low-emission formulations, public-awareness campaigns, and avoidance during severe air pollution reduce harm.

IX. Global atmospheric change

A. Global warming

Global warming is the long-term rise in Earth’s average surface temperature, mainly caused by increased greenhouse-gas concentrations.

• Mechanism: CO₂, methane (CH₄), nitrous oxide (N₂O), and fluorinated gases absorb outgoing infrared radiation and intensify the greenhouse effect.
• Sources: Coal, oil, and gas combustion; cement production; deforestation; livestock; rice cultivation; and landfills increase greenhouse gases.
• Evidence and effects: Rising temperatures contribute to glacier melt, sea-level rise, heatwaves, shifting rainfall, and increased wildfire risk.
• Controls: Renewable energy, efficiency, electrification, forest conservation, methane capture, carbon pricing, and low-carbon agriculture reduce emissions.

B. Climate change

Climate change includes long-term changes in temperature, rainfall, winds, extreme events, and ocean conditions; global warming is one major driver.

• Impacts: Droughts, floods, storms, heatwaves, sea-level rise, and ecosystem shifts threaten water, food, health, and infrastructure.
• Adaptation: Heat-action plans, drought-resistant crops, flood zoning, early-warning systems, water conservation, and climate-resilient buildings reduce vulnerability.
• Mitigation distinction: Mitigation addresses causes by reducing emissions; adaptation manages unavoidable effects.

C. Ozone layer depletion

Ozone depletion is the thinning of stratospheric ozone, which normally absorbs harmful ultraviolet-B radiation.

• Cause: Chlorofluorocarbons and halons release chlorine and bromine in the stratosphere; catalytic reactions destroy O₃ molecules.
• Effects: Increased UV-B raises skin-cancer and cataract risk, suppresses immunity, and damages phytoplankton and crops.
• Control: The Montreal Protocol reduced ozone-depleting substances; safe refrigerants, leak prevention, recovery, and proper disposal support recovery.

D. Acid rain

Acid rain is precipitation made unusually acidic when SO₂ and NOₓ react with water and oxygen to form sulfuric and nitric acids.

• Effects: Acidifies lakes and soils, leaches nutrients, releases toxic aluminium, damages forests, corrodes limestone buildings, and affects fish reproduction.
• Controls: Low-sulfur fuel, flue-gas desulfurisation, catalytic converters, renewable energy, and NOₓ control reduce precursor emissions.

X. Pollution impacts and evidence

A. Impacts on human communities and agriculture

Pollution distributes risks unequally, with children, older people, outdoor workers, low-income communities, and small farmers often facing greater exposure.

• Communities: Respiratory illness, unsafe water, reduced productivity, displacement, medical costs, and environmental injustice arise near roads, mines, landfills, and factories.
• Agriculture: O₃ reduces photosynthesis; acid deposition removes soil nutrients; contaminated irrigation water introduces salts, pathogens, and metals.
• Food security: Heat, drought, polluted soils, and declining pollinators reduce yields and increase food prices.
• Responses: Environmental impact assessment, community monitoring, clean technology, compensation, healthcare access, and participation improve environmental justice.

B. Case studies on pollution

Case studies show how pollutant pathways and governance determine outcomes.

• Minamata, Japan: Industrial mercury discharged into Minamata Bay bioaccumulated in fish, causing severe neurological disease; it demonstrates biomagnification and the need for industrial accountability.
• Great Smog of London, 1952: Coal smoke combined with stagnant weather, causing thousands of excess deaths and strengthening clean-air legislation.
• Bhopal, India, 1984: Methyl isocyanate gas escaped from a pesticide plant, causing deaths and long-term illness; it highlights hazardous-chemical management, emergency planning, and corporate responsibility.
• Cuyahoga River, United States: Repeated industrial fires, including the widely publicised 1969 fire, helped stimulate stronger water-pollution regulation.

XI. Solid waste management and waste control

A. Solid waste management

Solid waste management covers segregation, storage, collection, transport, recovery, treatment, and safe disposal of discarded materials.

• Hierarchy: Reduce, reuse, repair, recycle, recover energy, treat, and dispose; prevention is preferable to landfill.
• Segregation: Biodegradable, recyclable, hazardous, sanitary, and electronic wastes should be separated at source.
• Treatment: Composting and anaerobic digestion treat organic waste; material-recovery facilities sort recyclables; sanitary landfills use liners, leachate collection, and methane control.
• Circular economy: Product redesign, extended producer responsibility, repair systems, and recycling keep materials in use and reduce extraction.

B. Control measures of urban and industrial waste

Urban and industrial waste requires integrated planning because mixed waste increases treatment costs and environmental risk.

• Urban measures: Door-to-door segregated collection, composting, recycling centres, litter enforcement, wastewater treatment, and scientific landfilling prevent open dumping and burning.
• Industrial measures: Cleaner production, material substitution, process optimisation, waste audits, effluent treatment, hazardous-waste manifests, and secure storage control releases.
• Monitoring: Leachate, stack emissions, groundwater, worker exposure, and waste quantities should be regularly measured against legal standards.
• Polluter responsibility: The polluter-pays and precautionary principles encourage prevention, remediation, and financial responsibility for environmental damage.