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Pollution is the release of harmful environmental contaminants, or the substances so released. Generally the process needs to result from human activity to be regarded as pollution. Even relatively benign products of human activity are liable to be regarded as pollution, if they precipitate negative effects later on. The nitrogen oxides produced by industry are often referred to as pollution, for example, although the substances themselves are not harmful. In fact, it is solar energy (sunlight) that converts these compounds to smog.
Pollution can take two major forms: local pollution and global pollution. In the past, only local pollution was thought to be a problem. For example, coal burning produces smoke, which in sufficient concentrations can be a health hazard. One slogan, taught in schools, was "The solution to pollution is dilution". The theory was that sufficiently diluted pollution could cause no damage. In recent decades, awareness has been rising that some forms of pollution pose a global problem. For example, human activity (primarily nuclear testing) has significantly raised the levels of background radiation all over the world, which may lead to human health problems. Awareness of both kinds of pollution, among other things, has led to the environmentalism movement, which seeks to limit the human impact on the environment.
Whether something is pollution can depend on context. Blooms of algae and the resultant eutrophication of lakes and coastal ocean is considered pollution when it is fueled by nutrients from industrial, agricultural, or residential runoff.
Carbon dioxide emissions are sometimes referred to as pollution, on the basis that these emissions have led, or are leading, to raised levels of the gas in the atmosphere and, furthermore, to harmful changes in the Earth's climate. Such claims are strongly disputed, particularly by political conservatives in Western countries and most strongly in the United States. Due to this controversy, in many contexts carbon dioxide from such sources are labelled neutrally as "emissions." See global warming for a very extensive discussion of this topic.
Traditional forms of pollution include air pollution, water pollution, and radioactive contamination while a broader interpretation of the word has led to the ideas of ship pollution, light pollution and noise pollution.
Serious pollution sources include chemical plants, oil refineries, nuclear waste dumps, regular garbage dumps (many toxic substances are illegally dumped there), incinerators, PVC factories, car factories, plastics factories, corporate animal farms creating huge amounts of animal waste. Some sources of pollution, such as nuclear power plants or oil tankers, can release very severe pollution when accidents occur. Some of the more common contaminants are: chlorinated hydrocarbons (CFH), heavy metals like lead (in lead paint and until recently in gasoline), cadmium (in rechargeable batteries), chromium, zinc, arsenic and benzene.
Pollutants are thought to play a part in a variety of maladies, including: cancer, lupus, immune diseases, allergies, and asthma. Some illnesses are named in relation with certain pollutants: for example, Minamata disease caused by mercury compounds.
Regulation and Monitoring The United States Environmental Protection Agency (EPA) was supposed to establish "acceptable" levels of exposure to contaminants. One of the ratings chemicals are given are carcinogenicity, or how likely they are to cause cancer. Levels range from, not carcinogenic, likely carcinogen, known carcinogen, and unknown. But scientists are finding out that most of these levels are far too high and people should be exposed less to them. The CalEPA Office of Environmental Health Hazard Assessment has a list of more reasonable levels. (OEHHA (http://www.oehha.ca.gov/prop65/prop65_list/Newlist.html)). The U.S. has a maximum fine of US$25,000 for dumping toxic waste. However, many large manufacturers plead guilty, as they can easily afford this relatively small fine.
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