• Pollution is the introduction of contaminants into an environment, of whatever predetermined or agreed upon proportions or frame of reference; these contaminants cause instability, disorder, harm or discomfort.
  
  Pollution can take the form of chemical substances, or energy, such as noise, heat, or light energy.
  
  Pollutants, the elements of pollution, can be foreign substances or energies, or naturally occurring; when naturally occurring, they are considered contaminants when they exceed natural levels.
  Pollution is often classed as point source or nonpoint source pollution.
  Sometimes the term pollution is extended to include any substance when it occurs at such unnaturally high concentration within a system that it endangers the stability of that system. For example,
  1water is innocuous and essential for life, and yet at very high concentration, it could be considered a pollutant: if a person were to drink an excessive quantity of water, the physical system could be so overburdened that breakdown and even death could result.
  2 Another example is the potential of excessive noise to induce imbalance in a person's mental state, resulting in malfunction and psychosis; this has been used as a weapon in warfare.
  Pollution control
  Pollution control is a term used in environmental management. It means the control of emissions and effluents into air, water or soil. Without pollution control, the waste products from consumption, heating, agriculture, mining, manufacturing, transportation and other human activities, whether they accumulate or disperse, will degrade the natural environment. In the hierarchy of controls, pollution prevention and waste minimization are more desirable than pollution control.

Major forms of pollution and major polluted areas
The major forms of pollution are listed below along with the particular pollutants relevant to each of them:
1Air pollution, the release of chemicals and particulates into the atmosphere. Common air pollutants include carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs) and nitrogen oxides produced by industry and motor vehicles. Photochemical ozone and s mog are created as nitrogen oxides and hydrocarbons react to sunlight.
2Water pollution, by the release of waste products and contaminants into surface runoff into river drainage systems, leaching into groundwater, liquid spills, wastewater discharges, eutrophication and littering.
3Soi l contaminat ion occurs when chemicals are released by spill or underground leakage. Among the most significant soil contaminants are hydrocarbons, heavy metals, MTBE[4], herbicides, pesticides and chlorinated hydrocarbons.
4Radioactive contamination, resulting from 20th century activities in atomic physics, such as nuclear power generation and nuclear weapons research, manufacture and deployment. (See alpha emitters and actinides in the environment.)
5Noise pollution, which encompasses roadway noise, aircraft noise, industrial noise as well as high-intensity sonar.
The Blacksmith Institute issues annually a list of the world's worst polluted places. In the 2007 issues the ten top nominees are located in
1Azerbaijan, 2China, 3India, 4Peru, 5Russia, 6Ukraine 7Zambia

Sources and causes
Motor vehicle emissions are one of the leading causes of air pollution. China, United States, Russia, Mexico, and Japan are the world leaders in air pollution emissions; however, Canada is the number two country, ranked per capita.
Principal stationary pollution sources include chemical plants, coal-fired power plants, oil refineries,[3] petrochemical plants, nuclear waste disposal activity, incinerators, large livestock farms (dairy cows, pigs, poultry, etc.), PVC factories, metals production factories, plastics factories, and other heavy industry.
Some of the more common soil contaminants are chlorinated hydrocarbons (CFH), heavy metals (such as chromium, cadmium--found in rechargeable batteries, and lead--found in lead paint, aviation fuel and still in some countries, gasoline), MTBE, zinc, arsenic and benzene. Ordinary municipal landfills are the source of many chemical substances entering the soil environment.
groundwaterPollution can also be the consequence of a natural disaster. For example, hurricanes often involve water contamination from sewage, and petrochemical spills from ruptured boats or automobiles.
. Some sources of pollution, such as nuclear power plants or oil tankers, can produce widespread and potentially hazardous releases when accidents occur.
In the case of noise pollution the dominant source class is the motor vehicle, producing about ninety percent of all unwanted noise worldwide.
Effects
Human health
1Adverse air quality can kill many organisms including humans.
2Ozone pollution can cause respiratory disease, cardiovascular disease, throat inflammation, chest pain, and congestion.
3Water pollution causes approximately 14,000 deaths per day, mostly due to contamination of drinking water by untreated sewage in developing countries.
4Oil spills can cause skin irritations and rashes. Noise pollution induces hearing loss, high blood pressure, stress, and sleep disturbance.
Ecosystems
1Sulfur dioxide and oxides of nitrogen can cause acid rain which reduces the pH value of soil.
2Soil can become infertile and unsuitable for plants. This will affect other organisms in the food web.
3Smog and haze can reduce the amount of sunlight received by plants to carry out photosynthesis.
4Biomagnification describes a situation where toxins may be pass through trophic levels, becoming exponentially more concentrated in the process.
Regulation and monitoring
To protect the environment from the adverse effects of pollution, many nations worldwide have enacted legislation to regulate various types of pollution as well as to mitigate the adverse effects of pollution.
Regulation and monitoring by region
International
The Kyoto Protocol[9] is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC), an international treaty on global warming. It also reaffirms sections of the UNFCCC. Countries which ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.[9] A total of 141 countries have ratified the agreement. Notable exceptions include the United States and Australia, who have signed but not ratified the agreement. The stated reason for the United States not ratifying is the exemption of large emitters of greenhouse gases who are also developing countries, like China and India.[10]