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Coal tar

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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]

It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.[2]

Uses

Pavement sealcoat

Main article: Sealcoat

Coal tar is incorporated into some parking-lot sealcoat products, which are used to protect and beautify the underlying pavement.[3] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[3] Research [4] shows it is used in United States states from Alaska to Florida and several areas have banned its use in sealcoat products [5][6][7] including: The District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota and others.[8][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 (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

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".[10]

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol (acetaminophen).[11] 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.

Safety

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.[12]

According to the FDA, coal tar concentrations between 0.5% and 5% are considered safe[13] 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.[14][citation needed] Coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified,[15][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,[16] 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.[17]

Coal tar distillers

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:[18]

Names

Also known as liquor carbonis detergens (LCD),[19] and liquor picis carbonis [a] (LPC) by BP.[20]

See also

Notes

  1. ^ Latin: coal tar solution

References

  1. ^ "Toxicological profile for wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles" (PDF). U.S. Department of Health and Human Services. September 2002. Retrieved 8 March 2013.
  2. ^ "19th WHO Model List of Essential Medicines (April 2015)" (PDF). WHO. April 2015. Retrieved May 10, 2015.
  3. ^ 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.
  4. ^ 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. doi:10.1016/j.scitotenv.2010.08.014. PMID 21112613. Retrieved 8 March 2013.
  5. ^ "City of Austin Ordinance 20051117-070" (PDF). 17 November 2005. Retrieved 8 March 2013.
  6. ^ "District Bans Coal-Tar Pavement Products". 26 June 2009. Retrieved 8 March 2013.
  7. ^ "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.
  8. ^ "Coal Tar Free America – Bans". Retrieved 8 March 2013.
  9. ^ 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. {{cite conference}}: External link in |conferenceurl= (help); Unknown parameter |conferenceurl= ignored (|conference-url= suggested) (help)
  10. ^ "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.
  11. ^ "Pain relief: from coal tar to paracetamol". Royal Society of Chemistry. July 2005. Retrieved 8 March 2013.
  12. ^ "The battle to save coal tar in California". 3 December 2001. Archived from the original on 19 February 2012. Retrieved 8 March 2013. {{cite web}}: |archive-date= / |archive-url= timestamp mismatch; 29 October 2002 suggested (help)
  13. ^ FDA (1 April 2015). "Drug Products for the Control of Dandruff, Seborrheic Dermatitis, and Psoriasis". Retrieved 26 February 2016.
  14. ^ 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.
  15. ^ 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. {{cite web}}: Italic or bold markup not allowed in: |work= (help)
  16. ^ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 2008-08-22. p. 5. Retrieved 8 March 2013.
  17. ^ "CDC - NIOSH Pocket Guide to Chemical Hazards - Coal tar pitch volatiles". www.cdc.gov. Retrieved 2015-11-27.
  18. ^ Mike Smith. "GANSG - Coal Tar Distillers". Igg.org.uk. Retrieved 8 March 2013.
  19. ^ Paghdal KV; Schwartz RA (31 January 2009). "Topical tar: back to the future". PMID 19185953. Retrieved 8 March 2013.
  20. ^ Berenblum I (25 September 1948). "Liquor Picis Carbonis". British Medical Journal. 2 (4577): 601. doi:10.1136/bmj.2.4577.601. PMC 2091540. PMID 18882998.
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