Pollutants are the elements, molecules and particles involved in pollution - life can be harmed when exposed to these materials, and the effects of them on humans and plants are well known. Pollutants can be introduced into the environment in many ways, both naturally and by humans. What pollutants do once they are emitted into the atmosphere, soil or water supply is dependent on the type of pollutant, however it is useful to characterize them in the following way: Primary pollutants are emitted directly into the environment, while secondary pollutants are formed from primary pollutants and external factors.
Many pollutants are introduced into the environment in different ways, they have different and sometimes unique health effects and are found in different amounts. It is hard to briefly describe these for each chemical, however they can be read about on each pollutant's own page. Different types of pollutants include: