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[Imen23x]

Water pollution
Pollution is the release of environmental contaminants. The major forms of pollution include:
• air pollution, the release of chemicals and particulates into the atmosphere. Common examples include carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs), and nitrogen oxides produced by industry and motor vehicles. Ozone and smog are created as nitrogen oxides and hydrocarbons react to sunlight.
• water pollution via surface runoff and leaching to groundwater.
• Soil contamination occurs when chemicals are released by spill or underground storage tank leakage. Among the most significant soil contaminants are hydrocarbons, heavy ****ls, MTBE, herbicides, pesticides and chlorinated hydrocarbons.
• radioactive contamination, added in the wake of 20th-century discoveries in atomic physics. (See alpha emitters and actinides in the environment.)
• noise pollution, which encompasses roadway noise, aircraft noise, industrial noise as well as high-intensity sonar.
• light pollution, includes light trespass, over-illumination and astronomical interference.
• visual pollution, which can refer to the presence of overhead power lines, motorway billboards, scarred landforms (as from strip mining), open storage of junk or municipal solid waste.
Sources and causes

Air pollution

The Lachine Canal, in Montreal, is polluted
Motor vehicle emissions are likely the leading cause of air pollution. The U.S., Russia, Mexico, China and Japan are the world leaders in air pollution emissions; however, Canada is the number two country, ranked per capita. The EU has adopted stringent emissions controls.
Principal stationary pollution sources include chemical plants, coal-fired power plants, oil refineries, nuclear waste disposal activity, incinerators, large animal farms, PVC factories, ****ls production factories, plastics factories, and other heavy industry.
Some of the more common soil contaminants are chlorinated hydrocarbons (CFH), heavy ****ls (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 (and often groundwater), emanating from the wide variety of refuse accepted, especially substances illegally discarded there, or from pre-1970 landfills that may have been subject to little control in the U.S. or EU.
Pollution 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. Larger scale and environmental damage is not uncommon when coastal oil rigs or refineries are involved. 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 on human health
Pollutants can cause disease, including cancer, lupus, immune diseases, allergies, and asthma. Higher levels of background radiation have led to an increased incidence of cancer and mortality associated with it worldwide. Some illnesses are named for the places where specific pollutants were first formally implicated. One example is Minamata disease, which is caused by organic mercury compounds.
Adverse air quality can kill many organisms including humans. Ozone pollution can cause respiratory disease, cardiovascular disease, throat inflammation, chest pain and congestion. Water pollution causes approximately 14,000 deaths per day, mostly due to contamination of drinking water by untreated sewage in developing countries. Oil spills can cause skin irritations and rashes. Noise pollution induces hearing loss, high blood pressure, stress and sleep disturbance.
Perspectives
The earliest precursor of pollution generated by life forms would have been a natural function of their existence. The attendant consequences on viability and population levels fell within the sphere of natural selection. These would have included the demise of a population locally or ultimately, species extinction. Processes that were untenable would have resulted in a new balance brought about by changes and adaptations. At the extremes, for any form of life, consideration of pollution is superseded by that of survival.
For mankind, the factor of technology is a distinguishing and critical consideration, both as an enabler and an additional source of byproducts. Short of survival, human concerns include the range from quality of life to health hazards. Since science holds experimental demonstration to be definitive, modern treatment of toxicity or environmental harm involves defining a level at which an effect is observable. Common examples of fields where practical measurement is crucial include automobile emissions control, industrial exposure (eg OSHA PELs), toxicology (eg LD50), and medicine (eg medication and radiation doses).
"The solution to pollution is dilution", is a dictum which summarizes a traditional approach to pollution management whereby sufficiently diluted pollution is not harmful. [8] [9] It is well-suited to some other modern, locally-scoped applications such as laboratory safety procedure and hazardous material release emergency management. But it assumes that the dilutant is in virtually unlimited supply for the application or that resulting dilutions are acceptable in all cases.
Such simple treatment for environmental pollution on a wider scale might have had greater merit in earlier centuries when physical survival was often the highest imperative, human population and densities were lower, technologies were simpler and their byproducts more benign. But these are often no longer the case. Furthermore, advances have enabled measurement of concentrations not possible before. The use of statistical methods in evaluating outcomes has given currency to the principle of probable harm in cases where assessment is warranted but resorting to deterministic models is impractical or unfeasible. In addition, consideration of the environment beyond direct impact on human beings has gained prominence.
Yet in the absence of a superseding principle, this older approach predominates practices throughout the world. It is the basis by which to gauge concentrations of effluent for legal release, exceeding which penalties are assessed or restrictions applied. The regressive cases are those where a controlled level of release is too high or, if enforceable, is neglected. [10] Migration from pollution dilution to elimination in many cases is confronted by challenging economical and technological barriers.
Controversy
Industry and concerned citizens have battled for decades over the significance of various forms of pollution. Salient parameters of these disputes are whether:
• a given pollutant affects all people or simply a genetically vulnerable set.
• an effect is only specific to certain species.
• whether the effect is simple, or whether it causes linked secondary and tertiary effects, especially on biodiversity
• an effect will only be apparent in the future and is presently negligible.
• the threshold for harm is present.
• the pollutant is of direct harm or is a precursor.
• employment or economic prosperity will suffer if the pollutant is abated.
Blooms of algae and the resultant eutrophication of lakes and coastal ocean is considered pollution when it is caused by nutrients from industrial, agricultural, or residential runoff in either point source or nonpoint source form (see the article on eutrophication for more information).
Heavy ****ls such as lead and mercury have a role in geochemical cycles and they occur naturally. These ****ls may also be mined and, depending on their processing, may be released disruptively in large concentrations into an environment they had previously been absent from. Just as the effect of anthropogenic release of these ****ls into the environment may be considered 'polluting', similar environmental impacts could also occur in some areas due to either autochthonous or historically 'natural' geochemical activity.

Historical and projected CO2 emissions by country (1990-2025).
Source: Energy Information Administration.
Carbon dioxide, while vital for photosynthesis, is sometimes referred to as pollution, because raised levels of the gas in the atmosphere affect the Earth's climate. See global warming for an extensive discussion of this topic. Disruption of the environment can also highlight the connection between areas of pollution that would normally be classified separately, such as those of water and air. Recent studies have investigated the potential for long-term rising levels of atmospheric carbon dioxide to cause slight but critical increases in the acidity of ocean waters, and the possible effects of this on marine ecosystems.