A pollutant is a substance in the environment that by direct toxicity or by indirectly harming the ecosystem is considered to be harmful or dangerous to humans. Pollutants can be in the air, the soil or the water where they can be taken into the bodies of humans or into the bodies of animals or plants that we consume, causing secondary damage to us. It can also change the ecology of an area to the disadvantage of humans.
Airborne pollutants include emissions from industries, factories, automobiles and even items as small as aerosol cans. CFC (chlorofluorocarbon) molecules caused by the use of aerosol cans, foams refrigerators and air-conditioning units are believed to result in depletion of the ozone layer in the atmosphere which contributes to UV radiation damage. Other airborne pollutants include emissions like carbon monoxide from automobiles and tobacco smoke can cause complications such as asthma.
Many of the soil-related pollutants were once airborne substances that settled to the ground. Nitrates, sulfates, metals and organic substances fall to the earth an end up as soil or water pollutants. Other pollutants are nitrate-containing fertilizers. These can be absorbed by vegetation and crops that are eventually consumed by humans.
Some water-based pollutants are those that occur as a result of run-off from polluted soil into streams and eventually into lakes and rivers. Wastewater from homes and industries can contain organic and inorganic pollutants. Fish that must live in these areas consume these pollutants and become dangerous to eat. Freshwater fish are, in general, more likely to contain pollutants than ocean water but large oil spills by oil tankers can destroy large amounts of wildlife.
Mercury from coal-burning power plants can enter the air and eventually fall into the soil and the water where freshwater fish must live. Mercury in freshwater fish has become so high in some areas that there are limits on how many of these fish a person can consume over a period of time.
Another form of pollutant comes from accidents that happen in nuclear power plants. Large amounts of nuclear material are released into the environment, resulting in acute radioactivity poisoning or more chronic problems, such as cancer.
In the U.S., the Environmental Protection Agency (EPA) controls, in part, the clean-up processes necessary for industries and other sources of pollution. Industrial plants can be cited for allowing too many pollutants into the environment via their emissions or by dumping waste in unapproved areas.
Entire industries, such as the automotive industry, can be challenged to reduce the amount of pollutants released by automobiles. Certain pesticides have been banned due to their pollutant effects. Oil spills are cleaned up as much as possible to reduce the risk to wildlife. A near complete ban on the use of CFCs in certain products has been done to reduce the possible effect on the ozone layer.