Coal tar

Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. 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, about 200 substances in all.^[1]

Applications

Pavement Sealcoat

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.

Tar was a vital component of the first sealed, or "tarmac", roads. Coal tar was formerly used as one of the primary ingredients of Tarmacadam pavements, when mixed with ironworks slag.^[2] Today, petroleum derived binders and sealers are more commonly used. These sealers are used to extend the life and lower 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 heating or baking process of the green blocks as a part of commercial graphite production, most part of the coal tar binders gets vaporised and is generally burned in an incinerator to prevent release in the atmosphere as the 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),^[3] and liquor picis carbonis (Latin: coal tar solution) (LPD),^[4][5] 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 an OTC (over-the-counter drug) pharmaceutical and are subject to regulation by the United States Food and Drug Administration. Name 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;^[6] this must then be diluted in an ointment base such as petrolatum.

(Pine tar has historically also been used for this purpose, but has been banned as a medical product by the FDA, since no evidence was submitted proving it is effective.^[7])

Safety

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

According to the National Psoriasis Foundation and the FDA, coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp or skin conditions.^[8] Coal tar concentrations between 0.5% and 5% are safe and effective for psoriasis, and no scientific evidence suggests that the coal tar in the concentrations seen in non-prescription treatments is carcinogenic. The NPF states that coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified,^[9] 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,^[10] 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.

See also

• Creosote
• Cresolene
• Preservative
• Red 40
• Tar
• Sealcoat

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, page 19, September 2002
2. ^ John Sheail, ‘Hooley, Edgar Purnell (1860–1942)’, Oxford Dictionary of National Biography, online edn, Oxford University Press, Sept 2004 accessed 21 June 2010
3. ^ Paghdal & Schwartz, Topical tar: Back to the future, Dermatology and Pathology, August 2009
4. ^ British Pharmacopoeia (BP)
5. ^ British Medical Journal - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2091540/
6. ^ USP30-NF25 page 1817
7. ^ http://pinch.com/skin/docs/fda/FDA-OTC-ingredients-ban
8. ^ National Psoriasis Foundation, The battle to save coal tar in California, December 3, 2001.
9. ^ National Psoriasis Foundation: Tar
10. ^ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 2008-08-22. p. 5. http://www.medicinenet.com/sun-sensitive_drugs_photosensitivity_to_drugs/page5.htm. Retrieved 2010-09-22. 

External links

• Coal Tar Pitch Volatiles by OSHA
• Parking lots create sticky pollution problem by Erica Engelhaupt Environmental Science and Technology