A pollutant is a substance that contaminates air, water, or soil. It can be a gas, a liquid, a solid, or even energy like noise or heat. Pollutants come from human activities and natural sources. Volcanic ash, wildfire smoke, and radon gas are natural. Most of the pollution that concerns regulators comes from industry, agriculture, and transport.

Pollutants harm health and ecosystems. Some are toxic at low concentrations. Others accumulate over time. Lead, mercury, and arsenic are heavy metals that damage the nervous system. Nitrogen and phosphorus fertilize waterways and cause algal blooms. Carbon dioxide traps heat and drives climate change. The list is long and growing as new chemicals enter the market.

Regulation sets limits on pollutants. The Clean Air Act, Clean Water Act, and similar laws in other countries define acceptable levels. Monitoring networks track compliance. Enforcement is uneven. Some countries lack resources or political will. Pollution does not respect borders. A factory in one country can acidify lakes in another. International cooperation is essential.

Common types

• Air pollutants
• Water pollutants
• Soil contaminants
• Greenhouse gases
• Noise and light