Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It has both medical and industrial uses. It may be applied to the affected area to treat psoriasis and seborrheic dermatitis (dandruff). It may be used in combination with ultraviolet light therapy. Industrially it is a railway tie preservative and used in the surfacing of roads.
|Trade names||Balnetar, Cutar, others|
|Synonyms||liquor carbonis detergens (LCD)
liquor picis carbonis (LPC)
|AHFS/Drugs.com||Multum Consumer Information|
Side effects 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. The exact mechanism of action is unknown. It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds. It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.
Coal tar was discovered around 1665 and used for medical purposes as early as the 1800s. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Coal tar is available as a generic medication and over the counter. In the United Kingdom 125 ml of 5% shampoo costs the NHS about £1.89. In the United States a month of treatment costs less than $25 USD. Coal-tar was one of the key starting materials for the early pharmaceutical industry.
Coal tar is used in medicated shampoo, soap and ointment, as a treatment for dandruff and psoriasis, and 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".
Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol (acetaminophen). 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.
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. Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch. Research shows it is used in United States states from Alaska to Florida, but several areas have banned its use in sealcoat products,  including the District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota and others.
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 binder used in the graphite industry for making "green blocks" is coke oven volatiles (COV), a considerable portion of which 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 (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:
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. According to the FDA, coal tar concentrations between 0.5% and 5% are considered safe 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. While concerns have been found in animal studies, short-term treatments of humans have shown no significant increase in rates of cancer. It's possible that the skin can repair itself after short-term exposure to PAHs, but not after long-term exposure.
Working with coal tar such as during the paving of roads or when working on roofs increases the risk of cancer.
The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer. Both the U.S. Department of Health and Human Services and the state of California list coal tars as known human carcinogens.
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 actionEdit
Coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified.[better source needed] 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. Others include 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.
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.
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it was concluded that there is sufficient evidence in humans for the carcinogenicity of occupational exposures during paving and roofing with coal tar pitch.
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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.
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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
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Evidence for carcinogenicity to humans (sufficient)
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keratolytic agent that inhibits excessive proliferation of epidermal cells by reducing DNA synthesis and mitotic activity to normal levels
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...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament
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|Look up coal tar in Wiktionary, the free dictionary.|
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