Coal tar

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This article is part of the Coal Issues portal on SourceWatch, a project of CoalSwarm and the Center for Media and Democracy. See here for help on adding material to CoalSwarm.

Coal tar is a brown or black liquid of extremely high viscosity. Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas. Coal tars are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.[1]

Applications

Pavement Sealcoat

Coal tar is incorporated into some parking-lot sealcoat products, used to protect and beautify the underlying pavement.[2]‍ Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[3] Substantial concerns have been raised about the safety of this application of coal tar, given that coal tar is known to cause cancer in humans [4] and that several PAH compounds in coal tar are toxic to aquatic life. Defenders of coal-tar use in sealcoat have pointed out that humans are exposed to PAHs through many pathways, and similarly that the urban environment has many potential sources of PAHs.[2]

The primary use of coal tar based sealcoats is regional within the US[3] but federal research [5] shows it is used in states from Alaska to Florida and several areas have banned its use in sealcoat products [6] [7] [8] including: The District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota.[9]

Industrial

Being flammable, coal tar is sometimes used for heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.

Coal tar was a component of the first sealed roads. In its original development by Edgar Purnell Hooley, tarmac was tar covered with granite chips. Later the filler used was industrial slag. Today, petroleum derived binders and sealers are more commonly used. These sealers are used to extend the life and reduce maintenance cost associated with asphalt pavements, primarily in asphalt road paving, car parks and walkways.

A large part of the binders used in the graphite industry for making "Green Blocks" are Coke Oven Volatiles or COV. A considerable portion of these COV used as binders is coal tar. During the baking process of the green blocks as a part of commercial graphite production, most of the coal tar binders are vaporised and are generally burned in an incinerator to prevent release into the atmosphere, as COV and coal tar can be injurious to health.

Coal tar is also used to manufacture paints, synthetic dyes, and photographic materials.

Medical

Also known as liquor carbonis detergens (LCD),[10] and liquor picis carbonis (LPC) [11] it can be used in medicated shampoo, Wrights Coal Tar Soap, and ointment, as a treatment for dandruff and psoriasis, as well as being used to kill and repel head lice. When used as a medication in the United States, coal tar preparations are considered over-the-counter drug pharmaceuticals and are subject to regulation by the United States Food and Drug Administration. Named brands include Denorex, Balnetar, Psoriasin, Tegrin, T/Gel, and Neutar. When used in the extemporaneous preparation of topical medications, it is supplied in the form of Coal Tar Topical Solution United States Pharmacopeia, which consists of a 20% percentage solution of coal tar in alcohol, with an additional 5% w/v of polysorbate 80; this must then be diluted in an ointment base such as petrolatum.[12])

Safety

According to the International Agency for Research on Cancer, preparations that include more than five percent of crude coal tar are on their List of IARC Group 1 carcinogens.

In 40 urban lakes nationwide, scientists with the U.S. Geological Survey (USGS) found coal tar sealants account for about half of hazardous chemicals known as polycyclic aromatic hydrocarbons, or PAHs, while vehicle-related sources such as motor oil account for one-fourth. A 2013 Mahler and Baylor University study calculated that lifetime exposure to PAHs, via house dust, was 38 times higher for people living near coal-tar-sealed pavement than those who weren't. PAHs are toxic to mammals, birds, fish, frogs and plants, and seven are suspected human carcinogens.[13]

Resources

References

  1. Toxicological profile for wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles. U.S. Department of Health and Human Services (sep 2002). Retrieved on mar 8, 2013.
  2. 2.0 2.1 The Truth about Coaltar (2006). Retrieved on Mar 8, 2013.
  3. 3.0 3.1 Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health. U.S. Geological Survey Fact Sheet (Feb 2, 2011). Retrieved on Mar 8, 2013.
  4. Report on Carcinogens. National Toxicology Program, Department of Health and Human Services (2011). Retrieved on Mar 8, 2013.
  5. Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes. U.S. Geological Survey (Dec 15, 2010). Retrieved on Mar 8, 2013.
  6. {{cite web | url = http://www.austintexas.gov/sites/default/files/files/Watershed/coaltar_ordinance.pdf | title = City of Austin Ordinance 20051117-070 | date = Nov 17, 2005 | accessdate = Mar 8, 2013
  7. {{cite web | title = District Bans Coal-Tar Pavement Products | url = http://newsroom.dc.gov/show.aspx/agency/ddoe/section/2/release/17479 | date = Jun 26, 2009 | accessdate = Mar 8, 2013
  8. Ordinance 80 : Establishing Regulations on Coal Tar Sealcoat Products Application and Sale. Dane County Office of Lakes and Watersheds (Jul 1, 2007). Retrieved on Mar 8, 2013.
  9. Coal Tar Free America – Bans. Retrieved on Mar 8, 2013.
  10. Topical tar: back to the future (Jan 31, 2009). Retrieved on Mar 8, 2013.
  11. Berenblum I (Sep 25, 1948). Liquor Picis Carbonis. Retrieved on Mar 8, 2013.
  12. Clean-Up of Ineffective Ingredients in OTC Drug Products. Food and Drug Administration (Nov 7, 1990). Retrieved on Mar 8, 2013.
  13. Wendy Koch, "Toxic driveways? Cities ban coal tar sealants," USA Today, June 16, 2013.

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