Coal tar explained

Synonyms:liquor carbonis detergens (LCD)
liquor picis carbonis (LPC)[1]
Tradename:Balnetar, Cutar, others
Pregnancy Us:C
Routes Of Administration:Topical
Legal Us:OTC
Legal Us Comment:/ Rx-only
Cas Number:8007-45-2
Unii:R533ESO2EC
Atc Prefix:D05
Atc Suffix:AA
Chemspiderid:none

Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal.[2] It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoriasis and seborrheic dermatitis (dandruff). It may be used in combination with ultraviolet light therapy.[3] Industrially it is a railroad tie preservative and used in the surfacing of roads. Coal tar was listed as a known human carcinogen in the first Report on Carcinogens from the U.S. Federal Government, issued in 1980.[4]

Coal tar was discovered circa 1665 and used for medical purposes as early as the 1800s.[5] [6] Circa 1850, the discovery that it could be used as the main raw material for the synthesis of dyes engendered an entire industry.[7] It is on the World Health Organization's List of Essential Medicines.[8] Coal tar is available as a generic medication and over the counter.[9]

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.[10] The exact mechanism of action is unknown. It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.[11] It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.[12]

Composition

Coal tar is produced through thermal destruction (pyrolysis) of coal. Its composition varies with the process and type of coal used  - lignite, bituminous or anthracite.[13]

Coal tar is a mixture of approximately 10,000 chemicals, of which only about 50% have been identified.[14] Most of the chemical compounds are polycyclic aromatic hydrocarbon:[15] [16]

Others: benzene, toluene, xylenes, cumenes, coumarone, indene, benzofuran, naphthalene and methyl-naphthalenes, acenaphthene, fluorene, phenol, cresols, pyridine, picolines, phenanthracene, carbazole, quinolines, fluoranthene. Many of these constituents are known carcinogens.[18] [19]

Derivatives

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol aka acetaminophen.[20] Paracetamol may be the only coal-tar derived analgesic still in use today.[21] Industrial phenol is now usually synthesized from crude oil rather than coal tar.[22]

Coal tar derivatives are contra-indicated for people with the inherited red cell blood disorder glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), as they can cause oxidative stress leading to red blood cell breakdown.[23]

Mechanism of action

The exact mechanism of action is unknown. Coal tar is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.

It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin.[24]

Uses

Medicinal

Coal tar is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[8] Coal tar is generally available as a generic medication and over the counter.

Coal tar is used in medicated shampoo, soap and ointment. It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties. It may be applied topically as a treatment for dandruff and psoriasis, and to kill and repel head lice.[3] It may be used in combination with ultraviolet light therapy.

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).[12] [25] [26] 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.

Construction

See main article: Sealcoat.

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.

Coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement.[27] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[27] Research[28] shows it is used throughout the United States of America, however several areas have banned its use in sealcoat products,[29] [30] [31] including the District of Columbia; the city of Austin, Texas; Dane County, Wisconsin; the state of Washington; and several municipalities in Minnesota and others.[32] [33]

Industry

In modern times, coal tar is mostly traded as fuel and an application for tar, such as roofing. The total value of the trade in coal tar is around US$20 billion each year.[34]

Some British companies included:[41] [42]

Safety

Side effects of coal tar products include skin irritation, sun sensitivity, allergic reactions, and skin discoloration. It is unclear if use during pregnancy is safe for the baby and use during breastfeeding is not typically recommended.[43]

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.[44] According to the FDA, coal tar concentrations between 0.5% and 5% are considered safe[45] and effective for psoriasis.

Cancer

Long-term, consistent exposure to coal tar likely increases the risk of non-melanoma skin cancers.[46] Evidence is inconclusive whether medical coal tar, which does not remain on the skin for the long periods seen in occupational exposure, causes cancer, because there is insufficient data to make a judgment.[47] While coal tar consistently causes cancer in cohorts of workers with chronic occupational exposure, animal models, and mechanistic studies, the data on short-term use as medicine in humans has so far failed to show any consistently significant increase in rates of cancer.[47]

Coal tar contains many polycyclic aromatic hydrocarbons, and it is believed that their metabolites bind to DNA, damaging it. The PAHs found in coal tar and air pollution induce immunosenescence and cytotoxicity in epidermal cells.[48] [49] It's possible that the skin can repair itself from this damage after short-term exposure to PAHs but not after long-term exposure. Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma.

Coal tar was one of the first chemical substances proven to cause cancer from occupational exposure, during research in 1775 on the cause of chimney sweeps' carcinoma. Modern studies have shown that working with coal tar pitch, such as during the paving of roads or when working on roofs, increases the risk of cancer.[50]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.[51] [52] The U.S. Department of Health and Human Services lists coal tars as known human carcinogens.[53]

In response to public health concerns regarding the carcinogenicity of PAHs some municipalities, such as the city of Milwaukee, have banned the use of common coal tar-based road and driveway sealants citing concerns of elevated PAH content in groundwater.[54]

Other

Coal tar causes increased sensitivity to sunlight,[55] 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 13 January 2010 as a substance of very high concern by the European Chemicals Agency.[56]

Regulation

Exposure to coal tar pitch volatiles can occur in the workplace by breathing, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit) to 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.[57]

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 Food and Drug Administration (FDA).

See also

External links

Notes and References

  1. Berenblum I . Liquor picis carbonis; a carcinogenic agent . British Medical Journal . 2 . 4577 . 601 . September 1948 . 18882998 . 2091540 . 10.1136/bmj.2.4577.601 .
  2. Book: Vallee Y . Gas Phase Reactions in Organic Synthesis. 1998. CRC Press. 9789056990817. 107. en.
  3. Book: WHO Model Formulary 2008 . 2009 . 9789241547659 . ((World Health Organization)) . Stuart MC, Kouimtzi M, Hill SR . 10665/44053 . World Health Organization . World Health Organization . 308 .
  4. Book: First Annual Report on Carcinogens . 1980 . National Technical Reports Library.
  5. Book: Hornbostel C . Construction Materials: Types, Uses and Applications. 1991. John Wiley & Sons. 9780471851455. 864. en. live. https://web.archive.org/web/20170918185259/https://books.google.com/books?id=oaxKD0pEKxkC&pg=PA864. 2017-09-18.
  6. Book: Sneader W . Drug Discovery: A History. 2005. John Wiley & Sons. 9780471899792. 356. en. live. https://web.archive.org/web/20170918185259/https://books.google.com/books?id=Cb6BOkj9fK4C&pg=PA356. 2017-09-18.
  7. News: History The Early Years (1863–1881) . 4 February 2021 . Bayer AG.
  8. Book: ((World Health Organization)) . World Health Organization model list of essential medicines: 21st list 2019 . 2019 . 10665/325771 . World Health Organization . World Health Organization . Geneva . WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO . free .
  9. Book: Hamilton R . Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition. 2015. Jones & Bartlett Learning. 9781284057560. X.
  10. Web site: Coal Tar use while Breastfeeding Drugs.com. www.drugs.com. 13 January 2017. live. https://web.archive.org/web/20170118034352/https://www.drugs.com/breastfeeding/coal-tar.html. 18 January 2017.
  11. Web site: Background and Environmental Exposures to Creosote in the United States. cdc.gov. 13 January 2017. 19. September 2002. live. https://web.archive.org/web/20170125025514/https://www.atsdr.cdc.gov/ToxProfiles/tp85-c2.pdf. 25 January 2017.
  12. Book: Maibach HI . Evidence Based Dermatology. 2011. PMPH-USA. 9781607950394. 935–936. en. live. https://web.archive.org/web/20170918185259/https://books.google.com/books?id=V2L1MAoGHVkC&pg=PA935. 2017-09-18.
  13. Book: Encyclopedia of Toxicology. Roberts L . 2014. Academic Press. 9780123864550. Wexler P . Oxford. 993–995. 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.. Coal Tar. Third.
  14. May 1963. 10.1021/ie50641a006. Heinz-Gerhard F . The Challenge in Coal Tar Chemicals. Industrial & Engineering Chemistry. 55. 5. 38–44.
  15. Book: Creosote. . 2002 . Agency for Toxic Substances Disease Registry, Division of Toxicology, Dept. of Health and Human Services, Public Health Service . US . en . 816079578.
  16. Web site: September 2002 . Public Health Statement for Creosote . Agency for Toxic Substances and Disease Registry.
  17. Book: Kirk-Othmer Encyclopedia of Chemical Technology. Betts WD . John Wiley & Sons, Inc. . 1997. 9780471238966. 5th. New York. Tar and pitch. 10.1002/0471238961 .
  18. Web site: EUR-Lex - 32013R1272 - EN - EUR-Lex. eur-lex.europa.eu. en. https://web.archive.org/web/20151019180649/http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32013R1272. 2015-10-19. dead. 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.
  19. Web site: COAL TAR - National Library of Medicine HSDB Database. toxnet.nlm.nih.gov. 2017-06-10. live. https://web.archive.org/web/20170528211224/https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb%3A%40term+%40DOCNO+5050. 2017-05-28.
  20. Dronsfield A . 1 July 2005 . Pain relief: from coal tar to paracetamol . 42 . 4 . 102–105 . live . . . https://web.archive.org/web/20171013013607/https://eic.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article . 13 October 2017 . 14 June 2018.
  21. News: Brown T, Dronsfield A, Ellis P . Pain relief: from coal tar to paracetamol . Royal Society of Chemistry . 1 July 2005.
  22. Jones AW . Early drug discovery and the rise of pharmaceutical chemistry . Drug Testing and Analysis . 3 . 6 . 337–44 . June 2011 . 21698778 . 10.1002/dta.301 .
  23. Web site: US EPA National Center for Environmental Assessment . Hematologic Disorders . hero.epa.gov . 21 April 2020 . en . 15 March 2009.
  24. Web site: WHO Model Prescribing Information: Drugs Used in Skin Diseases: Keratoplastic and keratolytic agents: Coal tar. apps.who.int. 2017-06-10. keratolytic agent that inhibits excessive proliferation of epidermal cells by reducing DNA synthesis and mitotic activity to normal levels. dead. https://web.archive.org/web/20170420161122/http://apps.who.int/medicinedocs/en/d/Jh2918e/26.2.html#Jh2918e.26.2. 2017-04-20.
  25. Book: Clinical pharmacy : a practical approach - Society of Hospital Pharmacists of Australia. Hughes J, Donnelly R, James-Chatgilaou G . 2001. Macmillan Publishers Australia. 9780732980290. South Yarra. 114.
  26. Paghdal KV, Schwartz RA . Topical tar: back to the future . Journal of the American Academy of Dermatology . 61 . 2 . 294–302 . August 2009 . 19185953 . 10.1016/j.jaad.2008.11.024 .
  27. Web site: Mahler BJ, Van Metre PC . Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health. U.S. Geological Survey Fact Sheet. 2 February 2011. 8 March 2013. live. https://web.archive.org/web/20130328042236/http://pubs.usgs.gov/fs/2011/3010/. 2013-03-28.
  28. Van Metre PC, Mahler BJ . Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes . The Science of the Total Environment . 409 . 2 . 334–44 . December 2010 . 21112613 . 10.1016/j.scitotenv.2010.08.014 . 2010ScTEn.409..334V .
  29. Web site: City of Austin Ordinance 20051117-070. 17 November 2005. 8 March 2013. live. https://web.archive.org/web/20130531014726/http://austintexas.gov/sites/default/files/files/Watershed/coaltar_ordinance.pdf. 2013-05-31.
  30. Web site: District Bans Coal-Tar Pavement Products. 26 June 2009. 8 March 2013. live. https://web.archive.org/web/20121226213006/http://newsroom.dc.gov/show.aspx/agency/ddoe/section/2/release/17479. 2012-12-26.
  31. Web site: Dane County Office of Lakes and Watersheds. Ordinance 80 : Establishing Regulations on Coal Tar Sealcoat Products Application and Sale. 1 July 2007. 8 March 2013. live. https://web.archive.org/web/20110824044232/http://pdf.countyofdane.com/ordinances/ORD080.pdf. 2011-08-24.
  32. Web site: Coal Tar Free America – Bans. 8 March 2013. live. https://web.archive.org/web/20141006095421/http://coaltarfreeamerica.blogspot.com/p/bans.html. 2014-10-06.
  33. http://www.eesi.org/pahs-increasing-urban-us-lakes-14-apr-2011. PAHs Increasing in Urban U.S. Lakes. Causes of Increasing Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in U.S. Lakes. Mahler BJ . Environmental and Energy Study Institute. 14 April 2011. 8 March 2013. dead. https://web.archive.org/web/20111005105420/http://files.eesi.org/mahler_041411.pdf. 5 October 2011.
  34. Web site: Coal Tar Oil | OEC .
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  36. Book: Speight JG . Coal gasification processes for synthetic liquid fuel production . Luque R, Speight JG . Gasification for Synthetic Fuel Production . Woodhead Publishing Series in Energy . 2015 . 201–220 (212) . Woodhead . 978-0-85709-802-3 . 10.1016/B978-0-85709-802-3.00009-6 . 9.5.1 Coal tar chemicals: Coal tar is a black or dark brown liquid or a high-viscosity semi-solid that is one of the by-products formed when coal is carbonized. Coal tars are complex and variable mixtures of polycyclic aromatic hydrocarbons (PAHs), phenols, and heterocyclic compounds. Because of its flammable composition, coal tar is often used for fire boilers in order to create heat. They must be heated before any heavy oil flows easily..
  37. Web site: Market Study: Carbon Black . 2013-04-26 . Ceresana.
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  42. Web site: Smith M . GANSG – Coal Tar Distillers . Igg.org.uk . 8 March 2013 . dead . https://web.archive.org/web/20130619153801/http://www.igg.org.uk/gansg/12-linind/tardis.htm . 2013-06-19 .
  43. Web site: Coal Tar use while Breastfeeding . Drugs.com. 2 June 2023 . https://web.archive.org/web/20230926083525/https://www.drugs.com/breastfeeding/coal-tar.html . 26 September 2023. live.
  44. Web site: The battle to save coal tar in California. 3 December 2001. https://web.archive.org/web/20021029132630/http://www.psoriasis.org/coaltar.advocacy.htm. 2002-10-29. 8 March 2013. dead.
  45. Web site: Drug Products for the Control of Dandruff, Seborrheic Dermatitis, and Psoriasis. FDA. 1 April 2015. 26 February 2016. live. https://web.archive.org/web/20150918184253/http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=358&showFR=1&subpartNode=21%3A5.0.1.1.30.8. September 18, 2015.
  46. Moustafa GA, Xanthopoulou E, Riza E, Linos A . Skin disease after occupational dermal exposure to coal tar: a review of the scientific literature . International Journal of Dermatology . 54 . 8 . 868–79 . August 2015 . 26183242 . 10.1111/ijd.12903 . 205189697 . free .
  47. Roelofzen JH, Aben KK, Oldenhof UT, Coenraads PJ, Alkemade HA, van de Kerkhof PC, van der Valk PG, Kiemeney LA . 6 . No increased risk of cancer after coal tar treatment in patients with psoriasis or eczema . The Journal of Investigative Dermatology . 130 . 4 . 953–61 . April 2010 . 20016499 . 10.1038/jid.2009.389 . free .
  48. Pan TL, Wang PW, Aljuffali IA, Huang CT, Lee CW, Fang JY . The impact of urban particulate pollution on skin barrier function and the subsequent drug absorption . English . Journal of Dermatological Science . 78 . 1 . 51–60 . April 2015 . 25680853 . 10.1016/j.jdermsci.2015.01.011 .
  49. Qiao Y, Li Q, Du HY, Wang QW, Huang Y, Liu W . Airborne polycyclic aromatic hydrocarbons trigger human skin cells aging through aryl hydrocarbon receptor . Biochemical and Biophysical Research Communications . 488 . 3 . 445–452 . July 2017 . 28526404 . 10.1016/j.bbrc.2017.04.160 .
  50. Book: Coal-tar pitch. IARC. https://web.archive.org/web/20160521101818/http://monographs.iarc.fr/ENG/Monographs/vol100F/mono100F-17.pdf. 21 May 2016. live. 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. ... Six coal-tar pitches and three extracts of coal-tar pitches all produced skin tumours, including carcinomas, when applied to the skin of mice.
  51. Book: IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. . Chemical Agents and Related Occupations. . Lyon (FR) . International Agency for Research on Cancer . 2012 . IARC Monographs on the Evaluation of Carcinogenic Risks to Humans . 100F . Coal-Tar Pitch . https://www.ncbi.nlm.nih.gov/books/NBK304423/ .
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  53. Web site: Report on Carcinogens, Fourteenth Edition: Coal Tars and Coal-Tar Pitches. National Toxicology Program, Department of Health and Human Services. en-us. 2017-06-10. live. https://web.archive.org/web/20170201002821/https://ntp.niehs.nih.gov/ntp/roc/content/profiles/coaltars.pdf. 2017-02-01.
  54. News: Quirmbach C . Milwaukee Common Council Bans Coal Tar Sealants . Wisconsin Public Radio . 7 February 2017.
  55. Web site: Sun-Sensitive Drugs (Photosensitivity to Drugs) . 2008-08-22 . 5 . MedicineNet . . 8 March 2013 . live . https://web.archive.org/web/20130317004507/http://www.medicinenet.com/sun-sensitive_drugs_photosensitivity_to_drugs/page5.htm . 2013-03-17 .
  56. Web site: Candidate List of substances of very high concern for Authorisation . echa.europa.eu/home . nd . 27 October 2021.
  57. Web site: CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles. cdc.gov. 2015-11-27. live. https://web.archive.org/web/20151208120356/http://www.cdc.gov/niosh/npg/npgd0145.html. 2015-12-08.

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