Chemistry:Coal tar

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Short description: Chemical mixture
This page is about the substance. For the book, see Coal Tar: How Corrupt Politics and Corporate Greed Are Killing America's Children.

Coal tar
Clinical data
Trade namesBalnetar, Cutar, others
Other namesliquor carbonis detergens (LCD)
liquor picis carbonis (LPC)[1]
AHFS/Drugs.comMultum Consumer Information
Pregnancy
category
  • US: C (Risk not ruled out)
Routes of
administration		Topical
ATC code
Legal status
Legal status
  • US: OTC / Rx-only
Identifiers
CAS Number
ChemSpider
  • none
UNII

Coal tar (also creosote) is a thick dark liquid that is a by-product of deriving coke and coal gas from coal.[2][3] Coal tar has both medical and industrial uses.[2][4][5] Medicinally, it is a topical medication applied to skin to treat psoriasis and seborrheic dermatitis (dandruff).[4][5][6] It may be used in combination with ultraviolet light therapy in a treatment called Goeckerman therapy, which is rarely used clinically, as of 2024.[7]

Industrially, it is a railroad tie preservative used in the surfacing of roads.[8] Coal tar was listed as a known human carcinogen in the first Report on Carcinogens from the U.S. Federal Government, issued in 1980,[9] and remains a cancer concern due to the presence of benzene in coal tar skincare products, such as shampoos.[4][5][10]

History

Coal tar was discovered circa 1665.[8] Much later, it was an undesirable byproduct in the production of coke and illumination gases ("town gas"). Soon it was found that the tar could be a source of solvents.[11] Around 1850, it was discovered that it could be used as a source of many organic compounds. Its use as a precursor to dyes engendered an entire industry.[12] In 1854 Frederick Crace Calvert, "an eminent English chemist," made the extraordinary statement before the Society of Arts that ere long, some valuable dyeing substances would be prepared from coal."[13] Coal tar was used for medical purposes as early as the 1800s.[14]

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.[15]

Coal tar is a mixture of approximately 10,000 chemicals, of which only about 50% have been identified.[16] Most of the chemical compounds are polycyclic aromatic hydrocarbon:[17][18]

Others: benzene, toluene, xylenes, cumenes, coumarone, indene, benzofuran, naphthalene and methyl-naphthalenes, acenaphthene, fluorene, phenol, cresols, pyridine, picolines, phenanthracene, carbazole, quinolines, fluoranthene.[15] Many of these constituents are known carcinogens.[21][22]

Derivatives

Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol aka acetaminophen.[23] Paracetamol may be the only coal-tar derived analgesic still in use today.[24] Industrial phenol is now usually synthesized from crude oil rather than coal tar.[25]

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.[26]

Mechanism of action

The exact mechanism of action is unknown.[27] Coal tar is a complex mixture of phenols, polycyclic aromatic hydrocarbons, and heterocyclic compounds.[2]

It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin.[15][28]

Uses

Medicinal

Coal tar is on the World Health Organization's List of Essential Medicines.[6] Coal tar is generally available as a generic medication over the counter for topical use, typically as a shampoo.[4][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.[27][29][30] When used as a topical medication, it is supplied in the form of coal tar 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.

Coal tar is also used as a soap and ointment. It demonstrates antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.[27] It may be applied topically as a treatment for dandruff and psoriasis, and to kill and repel head lice.[4][5][6][31] It may be used in combination with ultraviolet light therapy called Goeckerman therapy.[6][7]

Although coal tar topical products have been used to treat childhood psoriasis, this is an uncommon clinical practice, with risk of cancer development existing from long-term treatment.[7] Coal tar as a monotherapy for childhood psoriasis has not been adequately studied.[7]

Adverse effects

Possible adverse effects of using topical coal tar to treat psoriasis include folliculitis, skin irritation, contact dermatitis, phototoxicity, and changes in skin pigmentation and odor.[4]

Construction

Main article: Chemistry:Sealcoat


Coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement.[32] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[32] Research[33] shows that it is used throughout the United States of America, but several areas have banned its use in sealcoat products,[34][35][36] including the District of Columbia; Austin, Texas; Dane County, Wisconsin; the state of Washington; and several municipalities in Minnesota and others.[37][38]

Industry

In modern times, coal tar is mostly traded as fuel and as an application for tar, such as roofing. The total value of the trade in coal tar is around US$20 billion per year (2023).[39]

  • Historically as a chemical feedstock for dyes.[40]
  • As a fuel.
  • In the manufacture of paints, synthetic dyes (notably tartrazine/Yellow #5), and photographic materials.[41]
  • For heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.[42]
  • As a source of carbon black.[43]
  • As a binder in manufacturing graphite; a considerable portion of the materials in "green blocks" is coke oven volatiles (COV). 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.[44][45]
  • As a main component of the electrode paste used in electric arc furnaces. Coal tar pitch act as the binder for solid filler that can be either coke or calcined anthracite, forming electrode paste, also widely known as Söderberg electrode paste.[46]
  • As a feed stock for higher-value fractions, such as naphtha, creosote and pitch. In the coal gas era, companies distilled coal tar to separate these out, leading to the discovery of many industrial chemicals.

Some British companies included:[47][48]

    • Bonnington Chemical Works
    • British Tar Products
    • Lancashire Tar Distillers
    • Midland Tar Distillers
    • Newton, Chambers & Company (owners of Izal brand disinfectant)
    • Sadlers Chemicals

Chemicals from coal tar

At one time, coal tar was a major source of organic compounds. This application has almost disappeared with the growth of the petrochemical industry. Coal tar is produced by thermolysis of coal, usually with the objective of obtaining coke, which is heavily used in the production of iron and steel. The tar is further processed, generating the following fractions of chemical interest: a mixture of benzene, toluene and xylenes ("BTX", phenolics, and polycyclic aromatics, especially naphthalene.[49]

Safety

Side effects include skin irritation, sun sensitivity, allergic reactions, and skin discoloration.[6] It is unclear if use during pregnancy is safe for the baby and its use during breastfeeding is not typically recommended.[50] The exact mechanism of action is unknown.[27] 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.[27]

Cancer

Long-term, consistent exposure to coal tar likely increases the risk of non-melanoma skin cancers.[51] Evidence is inconclusive as to 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.[52] While coal tar consistently causes cancer in cohorts of workers with chronic occupational exposure, animal models, and mechanistic studies,[19] the data on short-term use as medicine in humans has so far failed to show any consistently significant increase in rates of cancer.[52]

Coal tar contains many polycyclic aromatic hydrocarbons, and it is believed that their metabolites bind to DNA, damaging it.[22] The PAHs found in coal tar and air pollution induce immunosenescence and cytotoxicity in epidermal cells.[53][54] It is possible that the skin can repair itself from this damage after short-term exposure to PAHs but not after long-term exposure.[52] Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma.[15]

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.[15] 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.[19]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.[19][55][56] The U.S. Department of Health and Human Services lists coal tars as known human carcinogens.[57]

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.[58]

Other

Coal tar causes increased sensitivity to sunlight,[59] 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.[60]

Regulation

The U.S. 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 U.S. 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.[61]

See also

References

  1. ↑ "Liquor picis carbonis; a carcinogenic agent". British Medical Journal 2 (4577): 601. September 1948. doi:10.1136/bmj.2.4577.601. PMID 18882998. 
  2. ↑ 2.0 2.1 2.2 2.3 "ToxFAQs for Creosote". US Centers for Disease Control and Prevention. 8 July 2024. https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=65&toxid=18. 
  3. ↑ (in en) Gas Phase Reactions in Organic Synthesis. CRC Press. 1998. pp. 107. ISBN 978-90-5699-081-7. https://books.google.com/books?id=lfBC9hj9iH8C&pg=PA107. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 "Psoriasis treatment: Coal tar". American Association of Dermatology. 2025. https://www.aad.org/public/diseases/psoriasis/treatment/medications/coal-tar. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 "Management of Psoriasis With Topicals: Applying the 2020 AAD-NPF Guidelines of Care to Clinical Practice". Cutis 110 (2 Suppl): 8–14. August 2022. doi:10.12788/cutis.0573. PMID 36219602. https://www.mdedge.com/dermatology/article/256943/psoriasis/management-psoriasis-topicals-applying-2020-aad-npf-guidelines. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 WHO Model Formulary 2008. World Health Organization. 2009. pp. 306–308. ISBN 978-92-4-154765-9. https://iris.who.int/bitstream/10665/44053/1/9789241547659_eng.pdf. 
  7. ↑ 7.0 7.1 7.2 7.3 "Topical Management of Pediatric Psoriasis: A Review of New Developments and Existing Therapies". Paediatric Drugs 26 (1): 9–18. January 2024. doi:10.1007/s40272-023-00592-9. PMID 37847480. 
  8. ↑ 8.0 8.1 (in en) Construction Materials: Types, Uses and Applications. John Wiley & Sons. 1991. pp. 864. ISBN 978-0-471-85145-5. https://books.google.com/books?id=oaxKD0pEKxkC&pg=PA864. 
  9. ↑ First Annual Report on Carcinogens. National Technical Reports Library. 1980. https://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB84122852.xhtml. 
  10. ↑ "Coal tar and coal-tar pitch". US National Cancer Institute. 2025. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/coal-tar. 
  11. ↑ "Tar and Pitch". Ullmann's Encyclopedia of Industrial Chemistry. 2011. doi:10.1002/14356007.a26_091.pub2. ISBN 978-3-527-30673-2. 
  12. ↑ "History The Early Years (1863–1881)". Bayer AG. https://www.bayer.com/en/history/1863-1881. 
  13. ↑ "Dyes from Coal Tar Products". February 20, 2024. https://www.scientificamerican.com/article/dyes-from-coal-tar-products/. 
  14. ↑ (in en) Drug Discovery: A History. John Wiley & Sons. 2005. pp. 356. ISBN 978-0-471-89979-2. https://books.google.com/books?id=Cb6BOkj9fK4C&pg=PA356. 
  15. ↑ 15.0 15.1 15.2 15.3 15.4 "Coal Tar". Encyclopedia of Toxicology (Third ed.). Oxford: Academic Press. 2014. pp. 993–995. doi:10.1016/b978-0-12-386454-3.00012-9. ISBN 978-0-12-386455-0. "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." 
  16. ↑ "The Challenge in Coal Tar Chemicals". Industrial & Engineering Chemistry 55 (5): 38–44. May 1963. doi:10.1021/ie50641a006. 
  17. ↑ (in en) Creosote.. US: Agency for Toxic Substances Disease Registry, Division of Toxicology, Dept. of Health and Human Services, Public Health Service. 2002. OCLC 816079578. 
  18. ↑ "Public Health Statement for Creosote". Agency for Toxic Substances and Disease Registry. September 2002. https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=64&toxid=18. 
  19. ↑ 19.0 19.1 19.2 19.3 Coal-tar pitch. IARC. https://monographs.iarc.fr/ENG/Monographs/vol100F/mono100F-17.pdf. Retrieved 10 June 2017. "it was concluded that there is sufficient evidence in humans for the carcinogenicity of occupational exposures during paving and roofing with coal tar pitch. ... Six coal-tar pitches and three extracts of coal-tar pitches all produced skin tumours, including carcinomas, when applied to the skin of mice" 
  20. ↑ "Tar and pitch". Kirk-Othmer Encyclopedia of Chemical Technology (5th ed.). New York: John Wiley & Sons, Inc.. 1997. doi:10.1002/0471238961. ISBN 978-0-471-23896-6. 
  21. ↑ "EUR-Lex - 32013R1272 - EN - EUR-Lex" (in en). http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32013R1272. "...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament" 
  22. ↑ 22.0 22.1 "COAL TAR - National Library of Medicine HSDB Database". https://www.nlm.nih.gov/toxnet/index.html. 
  23. ↑ "Pain relief: from coal tar to paracetamol". Education in Chemistry (Royal Society of Chemistry) 42 (4): 102–105. 1 July 2005. https://eic.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article. Retrieved 14 June 2018. 
  24. ↑ "Pain relief: from coal tar to paracetamol". Royal Society of Chemistry. 1 July 2005. https://edu.rsc.org/feature/pain-relief-from-coal-tar-to-paracetamol/2020140.article. 
  25. ↑ "Early drug discovery and the rise of pharmaceutical chemistry". Drug Testing and Analysis 3 (6): 337–344. June 2011. doi:10.1002/dta.301. PMID 21698778. 
  26. ↑ "Hematologic Disorders" (in en). 15 March 2009. https://hero.epa.gov/hero/index.cfm/reference/details/reference_id/1390864. 
  27. ↑ 27.0 27.1 27.2 27.3 27.4 (in en) Evidence Based Dermatology. PMPH-USA. 2011. pp. 935–936. ISBN 978-1-60795-039-4. https://books.google.com/books?id=V2L1MAoGHVkC&pg=PA935. 
  28. ↑ "WHO Model Prescribing Information: Drugs Used in Skin Diseases: Keratoplastic and keratolytic agents: Coal tar". http://apps.who.int/medicinedocs/en/d/Jh2918e/26.2.html#Jh2918e.26.2. "keratolytic agent that inhibits excessive proliferation of epidermal cells by reducing DNA synthesis and mitotic activity to normal levels" 
  29. ↑ Clinical pharmacy : a practical approach - Society of Hospital Pharmacists of Australia. South Yarra: Macmillan Publishers Australia. 2001. pp. 114. ISBN 978-0-7329-8029-0. 
  30. ↑ "Topical tar: back to the future". Journal of the American Academy of Dermatology 61 (2): 294–302. August 2009. doi:10.1016/j.jaad.2008.11.024. PMID 19185953. 
  31. ↑ "Scalp psoriasis". National Psoriasis Foundation. 2025. https://www.psoriasis.org/scalp/#treatment-management. 
  32. ↑ 32.0 32.1 "Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health". U.S. Geological Survey Fact Sheet. 2 February 2011. http://pubs.usgs.gov/fs/2011/3010/. 
  33. ↑ "Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes". The Science of the Total Environment 409 (2): 334–344. December 2010. doi:10.1016/j.scitotenv.2010.08.014. PMID 21112613. Bibcode: 2010ScTEn.409..334V. 
  34. ↑ "City of Austin Ordinance 20051117-070". 17 November 2005. http://www.austintexas.gov/sites/default/files/files/Watershed/coaltar_ordinance.pdf. 
  35. ↑ "District Bans Coal-Tar Pavement Products". 26 June 2009. http://newsroom.dc.gov/show.aspx/agency/ddoe/section/2/release/17479. 
  36. ↑ "Ordinance 80 : Establishing Regulations on Coal Tar Sealcoat Products Application and Sale". Dane County Office of Lakes and Watersheds. 1 July 2007. http://pdf.countyofdane.com/ordinances/ORD080.pdf. 
  37. ↑ "Coal Tar Free America – Bans". https://coaltarfreeamerica.blogspot.com/p/bans.html. 
  38. ↑ "Causes of Increasing Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in U.S. Lakes". PAHs Increasing in Urban U.S. Lakes. Environmental and Energy Study Institute. 14 April 2011. http://files.eesi.org/mahler_041411.pdf. Retrieved 8 March 2013. 
  39. ↑ "Coal Tar Oil | OEC". https://oec.world/en/profile/hs/coal-tar-oil. 
  40. ↑ scientific american article/dyes-from-coal-tar-products/ June 1858
  41. ↑ Remediation of Former Manufactured Gas Plants and Other Coal-Tar Sites. Taylor & Francis Group. 2011. 
  42. ↑ "Coal gasification processes for synthetic liquid fuel production". Gasification for Synthetic Fuel Production. Woodhead Publishing Series in Energy. Woodhead. 2015. pp. 201–220 (212). doi:10.1016/B978-0-85709-802-3.00009-6. ISBN 978-0-85709-802-3. "9.5.1 Coal tar chemicals: Coal tar is a black or dark brown liquid or a high-viscosity semi-solid that is one of the by-products formed when coal is carbonized. Coal tars are complex and variable mixtures of polycyclic aromatic hydrocarbons (PAHs), phenols, and heterocyclic compounds. Because of its flammable composition, coal tar is often used for fire boilers in order to create heat. They must be heated before any heavy oil flows easily." 
  43. ↑ "Market Study: Carbon Black". Ceresana. http://www.ceresana.com/en/market-studies/chemicals/carbon-black/. 
  44. ↑ "CDC - Immediately Dangerous to Life or Health Concentrations (IDLH): Coal tar pitch volatiles - NIOSH Publications and Products" (in en-us). 2018-11-02. https://www.cdc.gov/niosh/idlh/65996932.html. 
  45. ↑ Asphalt materials science and technology. Amsterdam: Elsevier Science. 2015. pp. 60. ISBN 978-0-12-800501-9. OCLC 922698102. 
  46. ↑ "The use of thermomechanical analysis to characterise Söderberg electrode paste raw materials" (in en). Minerals Engineering 46-47: 167–176. June 2013. doi:10.1016/j.mineng.2013.04.016. ISSN 0892-6875. Bibcode: 2013MiEng..46..167B. 
  47. ↑ "Bonnington Chemical Works (1822-1878): Pioneer Coal Tar Company". International Journal for the History of Engineering & Technology 89 (1–2): 73–91. 2019. doi:10.1080/17581206.2020.1787807. 
  48. ↑ "GANSG – Coal Tar Distillers". Igg.org.uk. http://www.igg.org.uk/gansg/12-linind/tardis.htm. 
  49. ↑ "Chemicals from Coal Coking". Chemical Reviews 114 (3): 1608–1636. 2014. doi:10.1021/cr400256y. PMID 24080106. 
  50. ↑ "Coal Tar use while Breastfeeding | Drugs.com". https://www.drugs.com/breastfeeding/coal-tar.html. 
  51. ↑ "Skin disease after occupational dermal exposure to coal tar: a review of the scientific literature". International Journal of Dermatology 54 (8): 868–879. August 2015. doi:10.1111/ijd.12903. PMID 26183242. 
  52. ↑ 52.0 52.1 52.2 "No increased risk of cancer after coal tar treatment in patients with psoriasis or eczema". The Journal of Investigative Dermatology 130 (4): 953–961. April 2010. doi:10.1038/jid.2009.389. PMID 20016499. 
  53. ↑ "The impact of urban particulate pollution on skin barrier function and the subsequent drug absorption" (in English). Journal of Dermatological Science 78 (1): 51–60. April 2015. doi:10.1016/j.jdermsci.2015.01.011. PMID 25680853. 
  54. ↑ "Airborne polycyclic aromatic hydrocarbons trigger human skin cells aging through aryl hydrocarbon receptor". Biochemical and Biophysical Research Communications 488 (3): 445–452. July 2017. doi:10.1016/j.bbrc.2017.04.160. PMID 28526404. Bibcode: 2017BBRC..488..445Q. 
  55. ↑ "Chemical Agents and Related Occupations.". Coal-Tar Pitch. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Lyon (FR): International Agency for Research on Cancer. 2012. https://www.ncbi.nlm.nih.gov/books/NBK304423/. 
  56. ↑ "COAL-TARS (Group I)". IARC MONOGRAPHS SUPPLEMENT 7. IARC. 1987. pp. 175. ISBN 978-92-832-1411-3. https://monographs.iarc.fr/ENG/Monographs/suppl7/Suppl7-58.pdf. "Evidence for carcinogenicity to humans (sufficient)" 
  57. ↑ "Report on Carcinogens, Fourteenth Edition: Coal Tars and Coal-Tar Pitches" (in en-us). https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/coaltars.pdf. 
  58. ↑ "Milwaukee Common Council Bans Coal Tar Sealants". Wisconsin Public Radio. 7 February 2017. https://www.wiscontext.org/milwaukee-common-council-bans-coal-tar-sealants. 
  59. ↑ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 2008-08-22. pp. 5. http://www.medicinenet.com/sun-sensitive_drugs_photosensitivity_to_drugs/page5.htm. 
  60. ↑ "Candidate List of substances of very high concern for Authorisation". nd. https://echa.europa.eu/candidate-list-table/-/dislist/details/0b0236e1807d8743. 
  61. ↑ "CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles". https://www.cdc.gov/niosh/npg/npgd0145.html. 



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