The introduction of contaminants into the natural environment that causes adverse change is Pollution. A contaminant is a substance that is present where it should not be or present at concentrations above the background. All pollutants, i.e. the components of pollution, are contaminants, but not all contaminants are pollutants. Pollution can be from chemical substances, energy, noise, heat or light. Pollutants can be either foreign substances/energies or naturally occurring contaminants. Major forms of pollution include the following: Air pollution, light pollution, littering, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, visual pollution, and water pollution.
The emergence of great factories and consumption of immense quantities of coal gave rise to unprecedented air pollution and the large volume of industrial chemical discharges added to the growing load of untreated human waste.
Pollution introduced by light at night is becoming a global problem, more severe in urban centres, but contaminating large territories also, far away from cities and towns.
Growing evidence of local and global pollution and an increasingly informed public over time have given rise to environmentalism and the environmental movement, which generally seek to limit human impact on the environment. Three factors determine the severity of a pollutant: its chemical nature, the concentration, the area affected and the persistence.