A pollutant is a waste material that pollutes air, water or soil.
Three factors determine the severity of a pollutant: its chemical nature, the concentration and the persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the long term.
Pollutants that the environment has little or no absorptive capacity are called stock pollutants (eg. persistent synthetic chemicals, non-biodegradable plastics, and heavy metals). Stock pollutants accumulate in the environment over time. The damage they cause increases as more pollutant is emitted, and persists as the pollutant accumulates. Stock pollutants can create a burdon for future generations by passing on damage that persists well after the benefits received from incurring that damage have been forgotten.
Fund pollutants are those for which the environment has some absorptive capacity. Fund pollutants do not cause damage to the environment unless the emission rate exceeds the receiving environment's absorptive capacity (eg. carbon dioxide, which is absorbed by plants and oceans). Fund pollutants are not destroyed, but rather converted into less harmful substances, or diluted/dispersed to non-harmful concentrations.
Notable pollutants include the following groups:
Pollutants can also be defined by their zones of influence, both horizontally and vertically.
The horizontal zone refers to the the area that is damaged by a pollutant. Local pollutants cause damage near the emission source. Regional pollutants cause damage further from the emission source.
The vertical zone is referred to whether the damage is ground-level or atmospheric. Surface pollutants cause damage by concentrations of the pollutant accumulating near the earth's surface Global pollutants cause damage by concentrations in the atmosphere
Pollutants can cross international borders and therefore international regulations are needed for their control. The Stockholm Convention on Persistent Organic Pollutants, which entered into force in 2004, is an international legally binding agreement for the control of persistent organic pollutants. Pollutant Release and Transfer Registers (PRTR) are systems to collect and disseminate information on environmental releases and transfers of toxic chemicals from industrial and other facilities.
The European Pollutant Emission Register is a type of PRTR providing access to information on the annual emissions of industrial facilities in the Member States of the European Union, as well as Norway.
The National Ambient Air Quality Standards (NAAQS) are standards developed for outdoor air quality. The National Emissions Standards for Hazardous Air Pollutants are emission standards that are set by the Environmental Protection Agency which are not covered by the NAAQS.
Many pollutants have a poisonous effect on the body. Carbon monoxide is an example of a substance which is damaging to humans. This compound is taken up in the body instead of oxygen. That makes the body and in severe cases may lead to death.
Some pollutants became dangerous by reaction with other naturally occurring compounds. The oxides of nitrogen and sulfur are released from impurities in fossil fuels when they are burnt. They react with water vapor in the atmosphere to become acid rain. Acid rain damages buildings and makes lakes unable to support marine life, which causes fish and water plants to die.