Pollution

Environmental pollution refers to the introduction of harmful contaminants into natural ecosystems, resulting in adverse effects on living organisms, ecological processes, and the overall quality of air, water, and soil. Pollution may arise from substances in solid, liquid, or gaseous form, or from disruptive types of energy such as heat, sound, light, or radioactivity. While some pollutants originate from natural phenomena, the term most commonly describes contaminants generated by human activity, including industrial processes, agricultural practices, transportation systems, and inadequate waste management.

Characteristics and Sources of Pollution

Pollution encompasses a wide range of contaminants that may be either foreign to the environment or naturally occurring substances present at harmful concentrations. Human activities, particularly since the onset of industrialisation in the nineteenth and twentieth centuries, have markedly increased the release of pollutants. Many early industrial sources operated without regulation, producing legacy pollution that continues to affect ecosystems long after emissions ceased. Persistent organic pollutants, heavy metals, and other long-lived contaminants often remain in soils and water decades after their deposition.
Pollution is typically classified according to its origin. Point source pollution is emitted from identifiable locations, such as factories, wastewater outlets, or construction sites. By contrast, non-point source pollution arises from diffuse sources, including urban stormwater runoff, agricultural fields, and dispersed microplastics. Many forms of environmental degradation result from non-point sources, making mitigation and regulation significantly more complex.
Pollution exerts profound impacts on both human and environmental health. In 2019, approximately nine million premature deaths worldwide were attributed to pollution-related causes, with air pollution responsible for the majority. Vulnerable populations, including children, the elderly, and socioeconomically marginalised communities, face disproportionate risks due to the historical and contemporary siting of polluting industries near disadvantaged areas. These inequalities underpin the development of the environmental justice movement and continue to shape policy debates across the Global South and beyond.

Definitions and Frameworks

Definitions of pollution vary among international organisations and regulatory bodies. The United States Environmental Protection Agency characterises pollution as substances or energies that degrade environmental quality or pose health hazards. Such contamination diminishes the usefulness of natural resources and affects sensory qualities such as taste or smell. The United Nations adopts a broader definition, identifying pollution as the presence of substances or heat in air, water, or land at levels that produce undesirable environmental effects. These definitions reflect global concerns about air quality, water contamination, soil degradation, and the circulation of novel chemical entities.
Environmental pollution is closely linked to global sustainability objectives. Many of the United Nations Sustainable Development Goals address pollution mitigation through improvements in waste management, reductions in harmful chemicals, enhanced air and water standards, and increased access to clean energy.

Major Forms of Pollution

Pollution can manifest in numerous forms, each associated with specific contaminants and environmental consequences.
Air pollution involves emissions of gases and particulates from industrial facilities, vehicles, and energy production. Key pollutants include carbon monoxide, nitrogen oxides, sulphur dioxide, chlorofluorocarbons, and fine particulate matter (PM₁₀ and PM₂.₅). Secondary pollutants such as photochemical ozone and smog form when primary emissions react with sunlight.
Electromagnetic pollution arises from non-ionising electromagnetic radiation produced by telecommunications, broadcasting, and other electronic systems. Although direct harm to humans is minimal, such emissions can interfere with scientific instruments, including radioastronomy equipment.
Light pollution includes excessive or misdirected artificial light, causing ecological disruption and diminishing the visibility of the night sky. Light trespass and overillumination contribute to widespread impacts on wildlife behaviour and ecosystem function.
Litter represents improperly discarded materials, particularly plastics, deposited in public or private spaces.
Noise pollution stems from transport systems, industrial activity, and high-intensity sonar. Persistent noise exposure affects human health and disrupts wildlife communication and migration.
Plastic pollution comprises discarded plastic materials and microplastics, which accumulate in terrestrial and aquatic environments, posing risks to organisms through ingestion, entanglement, and chemical leaching.
Soil contamination arises from spills, industrial leakage, and the deposition of hazardous chemicals. Common soil contaminants include hydrocarbons, heavy metals such as lead and cadmium, herbicides, pesticides, and chlorinated compounds.
Radioactive contamination results from nuclear energy production, research activities, and weapons development. Radionuclides present long-term hazards due to their persistence and radiological properties.
Thermal pollution occurs when industrial processes alter the temperature of natural water bodies, often through the release of heated cooling water, disrupting aquatic ecosystems.
Visual pollution refers to intrusive or unsightly elements such as overhead power lines, billboards, scarred landscapes from mining, and accumulations of waste.
Water pollution includes contamination by untreated sewage, industrial effluents, agricultural run-off, and chemical spills. Polluted water can contain fertilizers, pesticides, pathogens, and toxic substances that harm ecosystems and threaten human health.

Natural Causes of Pollution

Although human activities dominate global pollution levels, natural processes also contribute to environmental contamination. Volcanoes release substantial quantities of gases, including carbon dioxide, hydrogen halides, sulphur dioxide, and hydrogen sulphide. These emissions can cause acid rain, respiratory hazards, and atmospheric alterations. Volcanic ash contains fine and ultrafine particles laced with toxic elements such as arsenic and mercury.
Wildfires, often ignited by lightning, are major sources of particulate matter, carbon dioxide, and carbon monoxide. Smoke from large fires can travel vast distances, impairing air quality and threatening the health of humans and wildlife.

Human-Generated Pollution

Human activities remain the principal drivers of pollution globally. Motor vehicles are significant contributors to air pollution, emitting particulates, nitrogen oxides, carbon monoxide, and other pollutants. Stationary industrial sources—including chemical production, metal smelting, petrochemical refining, power generation, and plastics manufacturing—release large volumes of contaminants into the atmosphere, soil, and water.
Agricultural practices contribute to pollution through the use of pesticides, herbicides, and fertilizers, as well as through land clearing and biomass burning. Large-scale animal husbandry generates methane and ammonia emissions, alongside substantial quantities of waste.
Global waste production continues to rise, with hundreds of millions of tonnes of hazardous waste generated annually. High-income countries produce disproportionately large quantities of carbon dioxide and municipal waste relative to their populations. Rapid industrial growth in countries such as China has shifted global emission patterns, although per capita pollution levels vary significantly across nations.
Common soil pollutants include chlorinated hydrocarbons, heavy metals, benzene, and additives such as methyl tert-butyl ether. Investigations into contaminated sites have revealed widespread distribution of hazardous substances in certain regions, requiring long-term remediation efforts.

Regulatory Responses

Pollution control relies on coordinated regulatory frameworks at the local, national, and international levels. Environmental agencies supervise air and water quality standards, enforce pollutant discharge limits, and monitor industrial compliance. International bodies such as the United Nations Environment Programme facilitate cooperation on global pollutants, including greenhouse gases and persistent organic pollutants.