Coal tar

Coal tar
Clinical data
Trade names Balnetar, Cutar, others
AHFS/Drugs.com Multum Consumer Information
Pregnancy
category
  • US: C (Risk not ruled out)
Routes of
administration		 Topical
ATC code
Legal status
Legal status
Identifiers
Synonyms liquor carbonis detergens (LCD)
liquor picis carbonis (LPC)[1]
CAS Number
ChemSpider
  • none

Coal tar is a very thick, dark liquid with a number of medical and industrial uses.[2][3] As a medication it is used to treat psoriasis and seborrheic dermatitis (dandruff).[4] For psoriasis it may be used together with ultraviolet light therapy.[4] It is used by application to the affected area.[4] Coal tar is one of the by-products when coal is made into coke and coal gas.[5] Industrial uses include preservation of railway ties and improving the surface of roads.[6]

Side effects include skin irritation, sun sensitivity, allergic reactions, and skin discoloration.[4] It is unclear if use during pregnancy is safe for the baby and use during breastfeeding is not typically recommended.[7] The exact mechanism of action is unknown.[8] It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.[2] It may have antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.[8]

Coal tar was discovered around 1665 and used for medical purposes as early as the 1800s.[6][9] It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[10] Coal tar is available as a generic medication and over the counter.[3] In the United Kingdom 125 ml of 5% shampoo costs the NHS about £1.89.[11] In the United States a month of treatment costs less than $25 USD.[3] Coal-tar was one of the key starting materials for the early pharmaceutical industry.[12]

Uses

Medicine

Coal tar may be used in two forms: crude coal tar (Latin: pix carbonis) or a coal tar solution (Latin: liquor picis carbonis, LPC) also known as liquor carbonis detergens (LCD).[8][13][14]

Coal tar is 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".[15]

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol (acetaminophen).[16] 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.

Construction

Coal tar is incorporated into some parking-lot sealcoat products, which are used to protect and beautify the underlying pavement.[17] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[17] Research [18] shows it is used in United States states from Alaska to Florida, but several areas have banned its use in sealcoat products, [19][20][21] including the District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota and others.[22][23]

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.

Industry

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 which are 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 (notably tartrazine/Yellow #5), and photographic materials.

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:[24]

Safety

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.[25] According to the FDA, coal tar concentrations between 0.5% and 5% are considered safe[26] and effective for psoriasis.

Cancer

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.[27] While concerns have been found in animals studies, short-term treatment of humans have shown no significant increase in cancer. It's possible that the skin can repair itself after short-term exposure to PAHs, but not after long-term exposure.[27]

Working with coal tar such as during the paving of roads or when working on roofs increases the risk of cancer.[28]

It is believed that their metabolites bind to DNA, damaging it. Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma.[29]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.[28][30][31] The U.S. Department of Health and Human Services lists coal tars as known human carcinogens.[32]

Other

Coal tar causes increased sensitivity to sunlight,[33] 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.

Mechanism of action

It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin.[34][29]

Composition

Coal tar contains many polycyclic aromatic hydrocarbons, such as benzopyrenes, benzanthracene, benzofluoranthenes, and chrysene, which are known carcinogens.[35][36]

Coal tar is produced through thermal destruction (pyrolysis) of coal, and the composition of coal tar varies with the process and type of coal (for example,: lignite, bituminous or anthracite) used to make it.[29]

It contains approximately 10,000 chemicals, of which only about 50% have been identified.[37] Components include polycyclic aromatic hydrocarbons (4-rings: chrysene, fluoranthene, pyrene, triphenylene, naphthacene, benzanthracene, 5-rings: picene, benzo[a]pyrene, benzo[e]pyrene, benzofluoranthenes, perylene, 6-rings: dibenzopyrenes, dibenzofluoranthenes, benzoperylenes, 7-rings: coronene), as well as methylated and polymethylated derivatives, mono- and polyhydroxylated derivatives, and heterocyclic compounds.[28][38] Others include benzene, toluene, xylenes, cumenes, coumarone, indene, benzofuran, naphthalene and methyl-naphthalenes, acenaphthene, fluorine, phenol, cresols, pyridine, picolines, phenanthracene, carbazole, quinolines, fluoranthene.[29]

History

It is notable as one of the first chemical substances proven to cause cancer from occupational exposure, during research in 1775 on the cause of chimney sweeps' carcinoma.[29]

Regulation

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.[39]

See also

References

  1. ↑ Berenblum I (25 September 1948). "Liquor Picis Carbonis". British Medical Journal. 2 (4577): 601. PMC 2091540 Freely accessible. PMID 18882998. doi:10.1136/bmj.2.4577.601.
  2. 1 2 "Background and Environmental Exposures to Creosote in the United States" (PDF). cdc.gov. September 2002. p. 19. Retrieved 13 January 2017.
  3. 1 2 3 Hamilton, Richart (2015). Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition. Jones & Bartlett Learning. p. X. ISBN 9781284057560.
  4. 1 2 3 4 WHO Model Formulary 2008 (PDF). World Health Organization. 2009. p. 308. ISBN 9789241547659. Retrieved 8 January 2017.
  5. ↑ Vallee, Yannick (1998). Gas Phase Reactions in Organic Synthesis. CRC Press. p. 107. ISBN 9789056990817.
  6. 1 2 Hornbostel, Caleb (1991). Construction Materials: Types, Uses and Applications. John Wiley & Sons. p. 864. ISBN 9780471851455.
  7. ↑ "Coal Tar use while Breastfeeding | Drugs.com". www.drugs.com. Retrieved 13 January 2017.
  8. 1 2 3 Maibach, Howard I. (2011). Evidence Based Dermatology. PMPH-USA. pp. 935–936. ISBN 9781607950394.
  9. ↑ Sneader, Walter (2005). Drug Discovery: A History. John Wiley & Sons. p. 356. ISBN 9780471899792.
  10. ↑ "WHO Model List of Essential Medicines (19th List)" (PDF). World Health Organization. April 2015. Retrieved 8 December 2016.
  11. ↑ British national formulary : BNF 69 (69 ed.). British Medical Association. 2015. p. 829. ISBN 9780857111562.
  12. ↑ Ravina, Enrique (2011). The Evolution of Drug Discovery: From Traditional Medicines to Modern Drugs. John Wiley & Sons. p. 23. ISBN 9783527326693.
  13. ↑ Hughes, Jeff; Donnelly, Richard; James-Chatgilaou, Greta (2001). Clinical pharmacy : a practical approach - Society of Hospital Pharmacists of Australia. South Yarra: Macmillan Publishers Australia. p. 114. ISBN 9780732980290.
  14. ↑ Paghdal KV; Schwartz RA (31 January 2009). "Topical tar: back to the future". J Am Acad Dermatol. 61 (2): 294–302. PMID 19185953. doi:10.1016/j.jaad.2008.11.024.
  15. ↑ "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.
  16. ↑ "Pain relief: from coal tar to paracetamol". Royal Society of Chemistry. July 2005. Retrieved 8 March 2013.
  17. 1 2 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.
  18. ↑ 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. PMID 21112613. doi:10.1016/j.scitotenv.2010.08.014.
  19. ↑ "City of Austin Ordinance 20051117-070" (PDF). 17 November 2005. Retrieved 8 March 2013.
  20. ↑ "District Bans Coal-Tar Pavement Products". 26 June 2009. Retrieved 8 March 2013.
  21. ↑ "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.
  22. ↑ "Coal Tar Free America – Bans". Retrieved 8 March 2013.
  23. ↑ 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.
  24. ↑ Mike Smith. "GANSG – Coal Tar Distillers". Igg.org.uk. Retrieved 8 March 2013.
  25. ↑ "The battle to save coal tar in California". 3 December 2001. Archived from the original on 2002-10-29. Retrieved 8 March 2013.
  26. ↑ FDA (1 April 2015). "Drug Products for the Control of Dandruff, Seborrheic Dermatitis, and Psoriasis". Retrieved 26 February 2016.
  27. 1 2 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. ISSN 0022-202X. PMID 20016499. doi:10.1038/jid.2009.389.
  28. 1 2 3 "Coal-tar pitch" (PDF). IARC. IARC. Retrieved 10 June 2017. it was concluded that there is sufficient evidence in humans for the carcinogenicity of occupational exposures during paving and roofing with coal tar pitch.
  29. 1 2 3 4 5 Roberts, L. (2014). Wexler, Philip, ed. Encyclopedia of Toxicology (Third Edition). Oxford: Academic Press. pp. 993–995. ISBN 9780123864550. doi:10.1016/b978-0-12-386454-3.00012-9. composition of coal tar will be influenced by the process used for pyrolytic distillation as well as by the original composition of the coal ... He then demonstrated excess cancers occurring in laboratory animals when coal tar is applied to the ears and skin ... [therapeutic effect] is thought to involve decreased epidermal proliferation ... Coal tar is classified as a human carcinogen ... Both inhalation and dermal routes of exposure are considered hazardous.
  30. ↑ "IARC Monographs- Classifications". monographs.iarc.fr. Retrieved 2017-06-10. CAS No.: 8007-45-2, Agent: Coal tars (see Coal-tar distillation), Volume: 35, Sup 7, Year: 1987, Agent: Coal-tar distillation, Group: 1, Volume: 92, 100F, Year: 2012
  31. ↑ "COAL-TARS (Group I)". IARC MONOGRAPHS SUPPLEMENT 7 (PDF). IARC. p. 175. Evidence for carcinogenicity to humans (sufficient)
  32. ↑ "Report on Carcinogens, Fourteenth Edition: Coal Tars and Coal-Tar Pitches" (PDF). National Toxicology Program, Department of Health and Human Services. Retrieved 2017-06-10.
  33. ↑ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 2008-08-22. p. 5. Retrieved 8 March 2013.
  34. ↑ "WHO Model Prescribing Information: Drugs Used in Skin Diseases: Keratoplastic and keratolytic agents: Coal tar". apps.who.int. Retrieved 2017-06-10. keratolytic agent that inhibits excessive proliferation of epidermal cells by reducing DNA synthesis and mitotic activity to normal levels
  35. ↑ "EUR-Lex - 32013R1272 - EN - EUR-Lex". eur-lex.europa.eu. Retrieved 2017-06-10. ...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament
  36. ↑ "COAL TAR - National Library of Medicine HSDB Database". toxnet.nlm.nih.gov. Retrieved 2017-06-10.
  37. ↑ 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.
  38. ↑ Betts, WD (1997). "Tar and pitch". Kirk-Othmer Encyclopedia of Chemical Technology (5th ed.). New York: John Wiley & Sons. ISBN 9780471238966. doi:10.1002/0471238961.
  39. ↑ "CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles". www.cdc.gov. Retrieved 2015-11-27.
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