Coal tar

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Coal tar
Clinical data
Trade names Balnetar, Cutar, others
Other namesliquor carbonis detergens (LCD)
liquor picis carbonis (LPC) [1]
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Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. [2] [3] It is a type of creosote. It has both medical and industrial uses. [2] [4] Medicinally it is a topical medication applied to skin to treat psoriasis and seborrheic dermatitis (dandruff). [5] It may be used in combination with ultraviolet light therapy. [5] Industrially it is a railroad tie preservative and used in the surfacing of roads. [6] Coal tar was listed as a known human carcinogen in the first Report on Carcinogens from the U.S. Federal Government, issued in 1980. [7]

Contents

Coal tar was discovered circa 1665 and used for medical purposes as early as the 1800s. [6] [8] Circa 1850, the discovery that it could be used as the main raw material for the synthesis of dyes engendered an entire industry. [9] It is on the World Health Organization's List of Essential Medicines. [10] Coal tar is available as a generic medication and over the counter. [4]

Side effects include skin irritation, sun sensitivity, allergic reactions, and skin discoloration. [5] It is unclear if use during pregnancy is safe for the baby and use during breastfeeding is not typically recommended. [11] The exact mechanism of action is unknown. [12] It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds. [2] 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] [ better source needed ] 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. [13] Many of these constituents are known carcinogens. [19] [20]

Derivatives

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol aka acetaminophen. [21] Paracetamol may be the only coal-tar derived analgesic still in use today. [22] Industrial phenol is now usually synthesized from crude oil rather than coal tar. [23]

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. [24]

Mechanism of action

The exact mechanism of action is unknown. [12] Coal tar is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds. [2]

It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin. [25] [13]

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. [10] Coal tar is generally available as a generic medication and over the counter. [4]

Coal tar is used in medicated shampoo, soap and ointment. It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties. [12] It may be applied topically as a treatment for dandruff and psoriasis, and to kill and repel head lice. [5] It may be used in combination with ultraviolet light therapy. [5]

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] [26] [27] 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

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.[ citation needed ]

Coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement. [28] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch. [28] Research [29] shows it is used throughout the United States of America, however several areas have banned its use in sealcoat products, [30] [31] [32] including the District of Columbia; the city of Austin, Texas; Dane County, Wisconsin; the state of Washington; and several municipalities in Minnesota and others. [33] [34]

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. [35]

Some British companies included: [41] [42]

Safety

Side effects of coal tar products include skin irritation, sun sensitivity, allergic reactions, and skin discoloration. [5] 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, [17] 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. [20] 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. [47] Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma. [13]

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. [13] 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. [17]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer. [17] [50] [51] The U.S. Department of Health and Human Services lists coal tars as known human carcinogens. [52]

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. [53]

Other

Coal tar causes increased sensitivity to sunlight, [54] 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. [55]

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. [56]

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

Related Research Articles

<span class="mw-page-title-main">Creosote</span> Tar distillation byproduct used as wood preservative

Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics.

<span class="mw-page-title-main">Naphthalene</span> Chemical compound

Naphthalene is an organic compound with formula C
10H
8. It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings. It is the main ingredient of traditional mothballs.

<span class="mw-page-title-main">Soot</span> Product of incomplete combustion of hydrocarbons

Soot is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed fuel particles such as coal, cenospheres, charred wood, and petroleum coke that may become airborne during pyrolysis and that are more properly identified as cokes or char.

<span class="mw-page-title-main">Phenanthrene</span> Polycyclic aromatic hydrocarbon composed of three fused benzene rings

Phenanthrene is a polycyclic aromatic hydrocarbon (PAH) with formula C14H10, consisting of three fused benzene rings. It is a colorless, crystal-like solid, but can also appear yellow. Phenanthrene is used to make dyes, plastics and pesticides, explosives and drugs. It has also been used to make bile acids, cholesterol and steroids.

<span class="mw-page-title-main">Polycyclic aromatic hydrocarbon</span> Hydrocarbon composed of multiple aromatic rings

A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar and planar. Many are colorless. Many of them are found in coal and in oil deposits, and are also produced by the incomplete combustion of organic matter—for example, in engines and incinerators or when biomass burns in forest fires.

<span class="mw-page-title-main">Carbon black</span> Chemical compound

Carbon black is a material produced by the incomplete combustion of coal tar, vegetable matter, or petroleum products, including fuel oil, fluid catalytic cracking tar, and ethylene cracking in a limited supply of air. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon. It is dissimilar to soot in its much higher surface-area-to-volume ratio and significantly lower polycyclic aromatic hydrocarbon (PAH) content. However, carbon black can be used as a model compound for diesel soot to better understand how diesel soot behaves under various reaction conditions as carbon black and diesel soot have some similar properties such as particle sizes, densities, and copolymer adsorption abilities that contribute to them having similar behaviours under various reactions such as oxidation experiments. Carbon black is used as a colorant and reinforcing filler in tires and other rubber products; pigment and wear protection additive in plastics, paints, and ink pigment. It is used in the EU as a food colorant when produced from vegetable matter (E153).

Benzo(<i>a</i>)pyrene Carcinogenic compound found in smoke and soot

Benzo[a]pyrene (BaP or B[a]P) is a polycyclic aromatic hydrocarbon and the result of incomplete combustion of organic matter at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F). The ubiquitous compound can be found in coal tar, tobacco smoke and many foods, especially grilled meats. The substance with the formula C20H12 is one of the benzopyrenes, formed by a benzene ring fused to pyrene. Its diol epoxide metabolites (more commonly known as BPDE) react with and bind to DNA, resulting in mutations and eventually cancer. It is listed as a Group 1 carcinogen by the IARC. In the 18th century a scrotal cancer of chimney sweepers, the chimney sweeps' carcinoma, was already known to be connected to soot.

Tar is the name for the resinous, combusted particulate matter made by the burning of tobacco and other plant material in the act of smoking. Tar is toxic and damages the smoker's lungs over time through various biochemical and mechanical processes. Tar also damages the mouth by rotting and blackening teeth, damaging gums, and desensitizing taste buds. Tar includes the majority of mutagenic and carcinogenic agents in tobacco smoke. Polycyclic aromatic hydrocarbons (PAH), for example, are genotoxic and epoxidative.

<span class="mw-page-title-main">Ethylbenzene</span> Hydrocarbon compound; precursor to styrene and polystyrene

Ethylbenzene is an organic compound with the formula C6H5CH2CH3. It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as a reaction intermediate in the production of styrene, the precursor to polystyrene, a common plastic material. In 2012, more than 99% of ethylbenzene produced was consumed in the production of styrene.

<span class="mw-page-title-main">Fluoranthene</span> Chemical compound

Fluoranthene is a polycyclic aromatic hydrocarbon (PAH). The molecule can be viewed as the fusion of naphthalene and benzene unit connected by a five-membered ring. Although samples are often pale yellow, the compound is colorless. It is soluble in nonpolar organic solvents. It is a member of the class of PAHs known as non-alternant PAHs because it has rings other than those with six carbon atoms. It is a structural isomer of the alternant PAH pyrene. It is not as thermodynamically stable as pyrene. Its name is derived from its fluorescence under UV light.

Occupational lung diseases comprise a broad group of diseases, including occupational asthma, industrial bronchitis, chronic obstructive pulmonary disease (COPD), bronchiolitis obliterans, inhalation injury, interstitial lung diseases, infections, lung cancer and mesothelioma. These can be caused directly or due to immunological response to an exposure to a variety of dusts, chemicals, proteins or organisms. Occupational cases of interstitial lung disease may be misdiagnosed as COPD, idiopathic pulmonary fibrosis, or a myriad of other diseases; leading to a delay in identification of the causative agent.

<span class="mw-page-title-main">DNA adduct</span> Segment of DNA bound to a cancer-causing chemical

In molecular genetics, a DNA adduct is a segment of DNA bound to a cancer-causing chemical. This process could lead to the development of cancerous cells, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers of exposure. They are especially useful in quantifying an organism's exposure to a carcinogen. The presence of such an adduct indicates prior exposure to a potential carcinogen, but it does not necessarily indicate the presence of cancer in the subject animal.

<span class="mw-page-title-main">Chrysene</span> Chemical compound

Chrysene is a polycyclic aromatic hydrocarbon (PAH) with the molecular formula C
18H
12 that consists of four fused benzene rings. It is a natural constituent of coal tar, from which it was first isolated and characterized. It is also found in creosote at levels of 0.5–6 mg/kg.

<span class="mw-page-title-main">Anthanthrene</span> Chemical compound

Anthanthrene is a polycyclic aromatic hydrocarbon. According to the International Agency for Research on Cancer, as of 2006 there was "limited evidence in experimental animals" that it is a carcinogen.

<span class="mw-page-title-main">Sealcoat</span>

Sealcoating, or pavement sealing, is the process of applying a protective coating to asphalt-based pavements to provide a layer of protection from the elements: water, oils, and U.V. damage.

<span class="mw-page-title-main">Benzopyrene</span>

A benzopyrene is an organic compound with the formula C20H12. Structurally speaking, the colorless isomers of benzopyrene are pentacyclic hydrocarbons and are fusion products of pyrene and a phenylene group. Two isomeric species of benzopyrene are benzo[a]pyrene and the less common benzo[e]pyrene. They belong to the chemical class of polycyclic aromatic hydrocarbons.

Benzo(<i>j</i>)fluoranthene Chemical compound

Benzo[j]fluoranthene (BjF) is an organic compound with the chemical formula C20H12. Classified as a polycyclic aromatic hydrocarbon (PAH), it is a colourless solid that is poorly soluble in most solvents. Impure samples can appear off white. Closely related isomeric compounds include benzo[a]fluoranthene (BaF), bendo[b]fluoranthene (BbF), benzo[e]fluoranthene (BeF), and benzo[k]fluoranthene (BkF). BjF is present in fossil fuels and is released during incomplete combustion of organic matter. It has been traced in the smoke of cigarettes, exhaust from gasoline engines, emissions from the combustion of various types of coal and emissions from oil heating, as well as an impurity in some oils such as soybean oil.

Benzo(<i>c</i>)fluorene Chemical compound

Benzo[c]fluorene is a polycyclic aromatic hydrocarbon (PAH) with mutagenic activity. It is a component of coal tar, cigarette smoke and smog and thought to be a major contributor to its carcinogenic properties. The mutagenicity of benzo[c]fluorene is mainly attributed to formation of metabolites that are reactive and capable of forming DNA adducts. According to the KEGG it is a group 3 carcinogen. Other names for benzo[c]fluorene are 7H-benzo[c]fluorene, 3,4-benzofluorene, and NSC 89264.

<span class="mw-page-title-main">National Firefighter Registry for Cancer</span> Registry of firefighters used to evaluate cancer risk

The National Firefighter Registry for Cancer (NFR) is a voluntary registry of firefighters in the United States used to evaluating cancer rates and cancer risk factors in the U.S. fire service through collecting relevant occupational, lifestyle, and health information on firefighters. It aims to use this data to reduce cancer in firefighters.

Indeno(1,2,3-<i>cd</i>)pyrene Polycyclic aromatic hydrocarbon

Indeno[1,2,3-cd]pyrene is a polycyclic aromatic hydrocarbon (PAH), one of 16 PAHs generally measured in studies of environmental exposure and air pollution. Many compounds of this class are formed when burning coal, oil, gas, wood, household waste and tobacco, and can bind to or form small particles in the air. The compounds are known to have toxic, mutagenic and/or carcinogenic properties. Over 100 different PAHs have been identified in environmental samples. One of these 16 is Indeno[1,2,3-cd]pyrene (IP). IP is the combination of an indeno molecule and a pyrene molecule with a fluoranthene network. In 1962, the National Cancer Institute reported that indeno[1,2,3-cd]pyrene has a slight tumor activity. This was confirmed in 1973 by the IARC in mice testing.

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  51. ↑ "COAL-TARS (Group I)" (PDF). IARC MONOGRAPHS SUPPLEMENT 7. IARC. p. 175. ISBN   9789283214113. Archived (PDF) from the original on 2016-03-15. Evidence for carcinogenicity to humans (sufficient)
  52. ↑ "Report on Carcinogens, Fourteenth Edition: Coal Tars and Coal-Tar Pitches" (PDF). National Toxicology Program, Department of Health and Human Services. Archived (PDF) from the original on 2017-02-01. Retrieved 2017-06-10.
  53. ↑ Quirmbach C (7 February 2017). "Milwaukee Common Council Bans Coal Tar Sealants". Wisconsin Public Radio.
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