Polycyclic Aromatic Hydrocarbons/Polararomatic Hydrocarbons (PAHs) Polycylic aromatic hydrocarbons, or PAHs, are a class of very stable organic molecules made up of only carbon and hydrogen. These molecules are flat, with each carbon having three neighboring atoms much like graphite. An example is the PAH coronene, with chemical symbol C24H12. These molecules are highly carcinogenic, but they are also very common. PAHs are a group of over 100 different chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances like tobacco or even charbroiled meat (such as benzoapyrene). PAHs are usually found as a mixture containing two or more of these compounds, such as soot. Some PAHs are manufactured. These pure PAHs usually exist as colorless, white, or pale yellow-green solids. PAHs are found in coal tar, crude oil, creosote, and roofing tar, but a few are used in medicines or to make dyes, plastics, and pesticides. PAHs are also present in marine conditions where heavy motorboat traffic exists. Some characteristics of PAHs are shown below: 1 PAHs enter the air mostly as releases from volcanoes, forest fires, burning coal, and automobile exhaust. 2 PAHs can occur in air attached to dust particles. 3 Some PAH particles can readily evaporate into the air from soil or surface waters. 4 PAHs can break down by reacting with sunlight and other chemicals in the air, over a period of days or weeks. 5 PAHs enter water through discharges from industrial and wastewater treatment plantsm or through marine engine exhaust releases. 6 Most PAHs do not dissolve easily in water. They stick to solid particles and settle to the bottoms of lakes or rivers. 7 Microorganisms can break down PAHs in soil or water after a period of weeks or months. 8 In soils, PAHs are most likely to stick tightly to particles, certain PAHs move through soil to contaminate underground water. 9 PAH contents of plants and animals may be much higher than PAH contents of soil or water in which they live, indicating a tendency towards Bioaccumulation.
Source: http://www.bvsde.paho.org/bvsacg/i/fulltext/dicciona/dicciona.pdf
Web site to visit: http://www.state.nv.us/cnr/ndwp/home.htm
Author of the Water Words Dictionary source of text: Gary A. Horton
If you are the author of the text above and you not agree to share your knowledge for teaching, research, scholarship (for fair use as indicated in the United States copyrigh low) please send us an e-mail and we will remove your text quickly. Fair use is a limitation and exception to the exclusive right granted by copyright law to the author of a creative work. In United States copyright law, fair use is a doctrine that permits limited use of copyrighted material without acquiring permission from the rights holders. Examples of fair use include commentary, search engines, criticism, news reporting, research, teaching, library archiving and scholarship. It provides for the legal, unlicensed citation or incorporation of copyrighted material in another author's work under a four-factor balancing test. (source: http://en.wikipedia.org/wiki/Fair_use)
The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.
The following texts are the property of their respective authors and we thank them for giving us the opportunity to share for free to students, teachers and users of the Web their texts will used only for illustrative educational and scientific purposes only.
All the information in our site are given for nonprofit educational purposes
The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.
www.riassuntini.com