Coal tar

Coal tar is a brown or black liquid of 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. It is a mixture of about 200 substances.

Applications

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.

Like pine tar, 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; this must then be diluted in an ointment base such as petrolatum. Coal tar is also used to synthesize paracetamol (acetaminophen). It is also used to manufacture paints,synthetic dyes and photographic materials.

Tar is used in treatment of the skin disease psoriasis, where coal tar is the most effective. Petroleum tar was also used in ancient Egyptian mummification circa 1000 BC.

Tar was a vital component of the first sealed, or "tarmac", roads. The streets of Baghdad were the first to be paved with tar from the 8th century AD. Coal tar was formerly used as one of the primary ingredients of Tarmacadam pavements, when mixed with ironworks slag. 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.

Safety

According to the International Agency for Research on Cancer, preparations that include more than 5 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. 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 , and the composition of coal tar varies with its origin and type of coal (eg: lignite, bituminous or anthracite) used to make it.

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

External links

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

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