Coal tar

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Coal tar
Clinical data
Trade names Balnetar, Cutar, others
AHFS/Drugs.com Multum Consumer Information
Pregnancy
category
  • US: C (Risk not ruled out)
ATC code D05AA (WHO)
Identifiers
CAS Number 8007-45-2

Coal tar is a dark very thick liquid with a number of medical and industrial uses.[1][2] As a medication it is used to treat psoriasis and seborrheic dermatitis (dandruff).[3] For psoriasis it may be used together with ultraviolet light therapy.[3] It is used by application to the affected area.[3] Industrial uses include preservation of railway ties and improving the surface of roads.[4]

Side effects include skin irritation, sun sensitivity, allergic reactions, and skin discoloration.[3] It is unclear if use during pregnancy is safe for the baby and use during breastfeeding is not typically recommended.[5] Coal tar is one of the by-products when coal is made into coke and coal gas.[6] It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.[1]

Coal tar was discovered around 1665 and used for medical purposes as early as the 1800s.[4][7] It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.[8] Coal tar is available as a generic medication and over the counter.[2] In the United Kingdom 125 ml of 5% shampoo costs the NHS about 1.89 pounds.[9] In the United States a month of treatment costs less than 25 USD.[2] Coal-tar was one of the key starting materials for the early pharmaceutical industry.[10]

Uses[edit]

Medical[edit]

It can be used in medicated shampoo, 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 U.S., coal tar preparations are considered over-the-counter drug pharmaceuticals and are subject to regulation by the FDA. 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 USP, which consists of a 20% w/v solution of coal tar in alcohol, with an additional 5% w/v of polysorbate 80 USP; this must then be diluted in an ointment base such as petrolatum.

Pine tar has historically also been used for this purpose. Though it is frequently cited online as having been banned as a medical product by the FDA due to a "lack of evidence having been submitted for proof of effectiveness", pine tar is included in the Code of Federal Regulations, subchapter D: Drugs for Human Use, as an OTC treatment for "Dandruff/seborrheic dermatitis/psoriasis".[11]

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol (acetaminophen).[12] Paracetamol is the only coal-tar derived analgesic still in use today, but industrial phenol is now usually synthesized from crude oil rather than coal tar.

Roads[edit]

Main article: Sealcoat

Coal tar is incorporated into some parking-lot sealcoat products, which are used to protect and beautify the underlying pavement.[13] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[13] Research [14] shows it is used in United States states from Alaska to Florida and several areas have banned its use in sealcoat products [15][16][17] including: The District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota and others.[18][19]

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.

Industrial[edit]

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.

A large part of the binders used in the graphite industry for making "green blocks" are coke oven volatiles (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.

Safety[edit]

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

According to the National Psoriasis Foundation, coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp or skin conditions.[20]

According to the FDA, coal tar concentrations between 0.5% and 5% are considered safe[21] and effective for psoriasis.

Scientific evidence is inconclusive whether the coal tar in the concentrations seen in non-prescription treatments is carcinogenic, because there are too few studies and insufficient data to make a judgement.[22][citation needed] Coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified,[23][better source needed] and the composition of coal tar varies with its origin and type of coal (for example,: lignite, bituminous or anthracite) used to make it.

Coal tar causes increased sensitivity to sunlight,[24] so skin treated with topical coal tar preparations should be protected from sunlight.

The residue from the distillation of high-temperature coal tar, primarily a complex mixture of three or more membered condensed ring aromatic hydrocarbons, was listed on 28 October 2008 as a substance of very high concern by the European Chemicals Agency.

People can be exposed to coal tar pitch volatiles in the workplace by breathing them in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for coal tar pitch volatiles exposure in the workplace as 0.2 mg/m3 benzene-soluble fraction over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 mg/m3 cyclohexane-extractable fraction over an 8-hour workday. At levels of 80 mg/m3, coal tar pitch volatiles are immediately dangerous to life and health.[25]

Coal tar distillers[edit]

In the coal gas era, there were many companies in Britain whose business was to distill coal tar to separate the higher-value fractions, such as naphtha, creosote and pitch. A great many industrial chemicals were first isolated from coal tar during this time. These companies included:[26]

Names[edit]

Also known as liquor carbonis detergens (LCD),[27] and liquor picis carbonis [a] (LPC) by BP.[28]

See also[edit]

Notes[edit]

  1. ^ Latin: coal tar solution

References[edit]

  1. ^ a b "Background and Environmental Exposures to Creosote in the United States" (PDF). cdc.gov. September 2002. p. 19. Retrieved 13 January 2017. 
  2. ^ a b c Hamilton, Richart (2015). Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition. Jones & Bartlett Learning. p. X. ISBN 9781284057560. 
  3. ^ a b c d WHO Model Formulary 2008 (PDF). World Health Organization. 2009. p. 308. ISBN 9789241547659. Retrieved 8 January 2017. 
  4. ^ a b Hornbostel, Caleb (1991). Construction Materials: Types, Uses and Applications. John Wiley & Sons. p. 864. ISBN 9780471851455. 
  5. ^ "Coal Tar use while Breastfeeding | Drugs.com". www.drugs.com. Retrieved 13 January 2017. 
  6. ^ Vallee, Yannick (1998). Gas Phase Reactions in Organic Synthesis. CRC Press. p. 107. ISBN 9789056990817. 
  7. ^ Sneader, Walter (2005). Drug Discovery: A History. John Wiley & Sons. p. 356. ISBN 9780471899792. 
  8. ^ "WHO Model List of Essential Medicines (19th List)" (PDF). World Health Organization. April 2015. Retrieved 8 December 2016. 
  9. ^ British national formulary : BNF 69 (69 ed.). British Medical Association. 2015. p. 829. ISBN 9780857111562. 
  10. ^ Ravina, Enrique (2011). The Evolution of Drug Discovery: From Traditional Medicines to Modern Drugs. John Wiley & Sons. p. 23. ISBN 9783527326693. 
  11. ^ "Title 21 – Food and Drugs. CHAPTER I – FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED): SUBCHAPTER D—DRUGS FOR HUMAN USE". United States Government Publishing Office. 1 March 2008. Retrieved 3 March 2016. 
  12. ^ "Pain relief: from coal tar to paracetamol". Royal Society of Chemistry. July 2005. Retrieved 8 March 2013. 
  13. ^ a b Mahler BJ; Van Metre PC (2 February 2011). "Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health". U.S. Geological Survey Fact Sheet. Retrieved 8 March 2013. 
  14. ^ Van Metre PC; Mahler BJ (15 December 2010). "Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes". U.S. Geological Survey. 409 (2): 334–44. doi:10.1016/j.scitotenv.2010.08.014. PMID 21112613. Retrieved 8 March 2013. 
  15. ^ "City of Austin Ordinance 20051117-070" (PDF). 17 November 2005. Retrieved 8 March 2013. 
  16. ^ "District Bans Coal-Tar Pavement Products". 26 June 2009. Retrieved 8 March 2013. 
  17. ^ "Ordinance 80 : Establishing Regulations on Coal Tar Sealcoat Products Application and Sale" (PDF). Dane County Office of Lakes and Watersheds. 1 July 2007. Retrieved 8 March 2013. 
  18. ^ "Coal Tar Free America – Bans". Retrieved 8 March 2013. 
  19. ^ Barbara J Mahler (14 April 2011). Causes of Increasing Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in U.S. Lakes (PDF). PAHs Increasing in Urban U.S. Lakes. Environmental and Energy Study Institute. Retrieved 8 March 2013. 
  20. ^ "The battle to save coal tar in California". 3 December 2001. Archived from the original on 19 February 2012. Retrieved 8 March 2013. 
  21. ^ FDA (1 April 2015). "Drug Products for the Control of Dandruff, Seborrheic Dermatitis, and Psoriasis". Retrieved 26 February 2016. 
  22. ^ Roelofzen, Judith H. J.; Aben, Katja K. H.; Oldenhof, Ursula T. H.; Coenraads, Pieter-Jan; Alkemade, Hans A.; Kerkhof, Peter C. M. van de; Valk, Pieter G. M. van der; Kiemeney, Lambertus A. L. M. (2010-04-01). "No Increased Risk of Cancer after Coal Tar Treatment in Patients with Psoriasis or Eczema". Journal of Investigative Dermatology. 130 (4): 953–961. doi:10.1038/jid.2009.389. ISSN 0022-202X. PMID 20016499. 
  23. ^ Heinz-Gerhard Franck (May 1963). "THE CHALLENGE IN COAL TAR CHEMICALS". Ind. Eng. Chem., 1963, 55 (5), pp 38–44. American Chemical Society. doi:10.1021/ie50641a006. Retrieved 8 March 2013. 
  24. ^ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 2008-08-22. p. 5. Retrieved 8 March 2013. 
  25. ^ "CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles". www.cdc.gov. Retrieved 2015-11-27. 
  26. ^ Mike Smith. "GANSG – Coal Tar Distillers". Igg.org.uk. Retrieved 8 March 2013. 
  27. ^ Paghdal KV; Schwartz RA (31 January 2009). "Topical tar: back to the future". J Am Acad Dermatol. 61 (2): 294–302. doi:10.1016/j.jaad.2008.11.024. PMID 19185953. Retrieved 8 March 2013. 
  28. ^ Berenblum I (25 September 1948). "Liquor Picis Carbonis". British Medical Journal. 2 (4577): 601. doi:10.1136/bmj.2.4577.601. PMC 2091540Freely accessible. PMID 18882998. 

External links[edit]