Pollution is the presence of particles or elements in a natural environment and thereby degrading the quality of it. It causes adverse changes to natural environment. Pollution is caused by contaminants and they can be of various types. Contaminants can be particles like chemical substances, gases or energy. They can be foreign substances or naturally occurring ones. Depending on the kind of contaminants and the environment, there are different forms of pollution – air pollution, light pollution, litter, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, visual pollution, and water pollution.

Pollution exists mainly in urban societies. The burning of coal and wood increase carbon content in air and make the cities the primary sources of pollution. The Industrial Revolution had brought an infusion of untreated chemicals and wastes into local water resources which supplied water to the people. Early instances include the time when King Edward I of England banned the burning of sea-coal by proclamation in London in 1272, after its smoke became a problem.

The major forms of pollution are described as follows:

Air pollution – It is caused by the release of chemicals and particulates into the atmosphere. Common gaseous pollutants are carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs) and nitrogen oxides which are produced by industry and motor vehicles.

Electromagnetic pollution – It is caused due to the overabundance of electromagnetic radiation in their non-ionizing form, like radio waves, etc. Nowadays people are constantly exposed to these radiations.

Light pollution – It includes light trespass, over-illumination and astronomical interference. There have been instances when over illumination of a natural environment by artificial lights have caused birds to be awake at night. It disturbs their natural time cycle.

Noise pollution – It includes noise from all sorts of sources like roadway noise, aircraft noise, industrial noise as well as high-intensity sonar.

Plastic pollution – This involves the accumulation of plastic products and microplastics in the environment and thereby affecting the wildlife, wildlife habitat, and humans.

Soil contamination – It is caused by chemicals released by spills or underground leakages. Among the most significant soil contaminants are hydrocarbons, heavy metals, MTBE herbicides, pesticides and chlorinated hydrocarbons.

Radioactive contamination – This has increased the 20th century due to activities in atomic physics, such as nuclear power generation and nuclear weapons research, manufacture and deployment.

Thermal pollution – This is a temperature change in natural water bodies. The most common reason is human influence. For example, the use of water as coolant in a power plant.

Visual pollution – It refers to the presence of overhead power lines, motorway billboards, scarred landform, open storage of trash, municipal solid waste or space debris.

Water pollution – It is caused by the discharge of wastewater from commercial and industrial factories into surface waters resources. It also includes discharges of untreated domestic sewage, and chemical contaminants, such as chlorine, treated sewage; pesticides and fertilizer components reaching water bodies through irrigation water. Groundwater pollution is caused from waste disposal including pit latrines and septic tanks; eutrophication and littering.

With growing evidence of local and global pollution, more and more people have started getting informed over time. Issues such as global warming and climate change have also developed in recent years. These have given rise to environmentalism and environmental movements. There are environmental activists who work to raise awareness and to limit human impact on the environment.