pollutant

A pollutant is a substance or energy form that degrades environmental quality or harms living organisms when present above acceptable levels. They may be chemical compounds, particulates, heat, noise, or biological agents. Pollutants can arise from natural sources such as volcanoes or wildfires, but many come from human activities like industry, agriculture, energy production, and transport. They affect air, water, soil, and ecosystems, and outcomes depend on dose, exposure duration, and receptor sensitivity.

Categories include air pollutants (carbon monoxide, sulfur dioxide, nitrogen oxides, ozone, fine particulates), water pollutants (nutrients causing eutrophication, heavy metals such as lead and mercury, pesticides, pathogens, salts), and soil pollutants (pesticides, hydrocarbons, trace metals). Emerging pollutants such as microplastics and PFAS are of growing concern due to persistence and potential health effects.

Pollution sources include industry emissions, power generation, vehicles, agricultural runoff, waste disposal, and spills. Pollutants reach receptors mainly by inhalation, ingestion, dermal contact, or via contaminated water and soil. Risk depends on hazard and the level, duration, and route of exposure.

Regulations set standards for ambient concentrations in air and water, discharge limits, and maximum contaminant levels in drinking water. Monitoring and risk assessment guide decisions on control, remediation, and protection of ecosystems. Mitigation approaches include emission controls, wastewater treatment, soil remediation, and preventive practices.

Understanding pollutants requires chemistry, toxicology, ecology, and environmental engineering. The field emphasizes reducing emissions, preventing releases, and evaluating long-term and indirect effects on health and ecosystems.