pollutant

thumb|Surface runoff, also called [[nonpoint source pollution, from a farm field in Iowa, the United States during a rainstorm. Topsoil, as well as farm fertilizers and other potential pollutants, runoff unprotected farm fields when heavy rains occur.|400x400px]]

A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oil) or anthropogenic in origin (i.e. manufactured materials or byproducts). Pollutants result in environmental pollution or become of public health concern when they reach a concentration high enough to have significant negative impacts.