A substance that pollutes something, especially water or the atmosphere. The factory was fined for releasing a harmful pollutant into the river.
Any energy or substance introduced into the environment that causes undesired effects or harms living organisms. Carbon monoxide is a common airborne pollutant that can be lethal at high concentrations.
A contaminant that renders something impure or unclean. Heavy metals act as persistent pollutants in many river sediments.