Triclosan

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Triclosan
File:Triclosan.svg
File:Triclosan-3D-vdW.png
IUPAC name
5-chloro-2-(2,4-dichlorophenoxy)phenol
Other names
2,4,4'-trichloro-2'-hydroxydiphenyl ether, 5-chloro-(2,4-dichlorophenoxy)phenol, trichloro-2'-hydroxydiphenyl ether, CH-3565, Lexol 300, Irgasan DP 300
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 3380-34-5 YesY
PubChem 5564
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style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula C12H7Cl3O2
Molar mass 289.54 g/mol
Melting point

55-57 °C

Boiling point

120 °C, 393 K, 248 °F

 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Triclosan is an antibacterial and antifungal agent. It is a polychloro phenoxy phenol. Despite being used in many consumer products, beyond its use in toothpaste to prevent gingivitis, there is no evidence according to the American Food and Drug Administration (FDA) that triclosan provides an extra benefit to health in other consumer products.[1] Triclosan safety is currently under review by the FDA.[1]

Chemical structure and properties

This organic compound is a white powdered solid with a slight aromatic/phenolic odor. It is a chlorinated aromatic compound which has functional groups representative of both ethers and phenols. Phenols often show antibacterial properties. Triclosan is only slightly soluble in water, but soluble in ethanol, methanol, diethyl ether, and stronger basic solutions such as 1 M sodium hydroxide. Triclosan can be synthesized from 2,4-dichlorophenol.

Uses

Triclosan has been used since 1972, and it is present in soaps (0.10-1.00%), deodorants, toothpastes, shaving creams, mouth washes, and cleaning supplies, and is infused in an increasing number of consumer products, such as kitchen utensils, toys, bedding, socks, and trash bags.[2] Triclosan has been shown to be effective in reducing and controlling bacterial contamination on the hands and on treated products. More recently, showering or bathing with 2% triclosan has become a recommended regimen for the decolonization of patients whose skin is carrying methicillin resistant Staphylococcus aureus (MRSA)[3] following the successful control of MRSA outbreaks in several clinical settings.[4][5]

Triclosan is regulated by the U.S. Food and Drug Administration, the Environmental Protection Agency, and the European Union. During wastewater treatment, a portion of triclosan is degraded, while the remaining adsorbs to sewage sludge or exits the plant in wastewater effluent.[6][7] In the environment, triclosan may be degraded by microorganisms or react with sunlight, forming other compounds, which include between 3 to 12 % of chlorophenols and dioxin (Particulary 2,8-dichlorodibenzo-p-dioxin (external) (2,8-DCDD) and 2,4-dichlorophenol (2,4-DCP) are produced. Both also are photolabile and, thus, are intermediates.), or it may adsorb to particles that settle out of the water column and form sediment.[6][8] Triclosan was found in Greifensee sediment that was over 30 years old, suggesting that triclosan is degraded or removed slowly in sediment.[6]

Mechanism of action

At in-use concentrations, triclosan acts as a biocide, with multiple cytoplasmic and membrane targets.[9] At lower concentrations, however, triclosan appears bacteriostatic and is seen to target bacteria mainly by inhibiting fatty acid synthesis. Triclosan binds to bacterial enoyl-acyl carrier protein reductase enzyme (ENR), which is encoded by the gene FabI. This binding increases the enzyme's affinity for nicotinamide adenine dinucleotide (NAD+). This results in the formation of a stable ternary complex of ENR-NAD+-triclosan, which is unable to participate in fatty acid synthesis. Fatty acids are necessary for reproducing and building cell membranes. Humans do not have an ENR enzyme, and thus are not affected. Some bacterial species can develop low-level resistance to triclosan at its lower bacteriostatic concentrations due to FabI mutations, which results in a decrease of triclosan's effect on ENR-NAD+ binding, as shown in Escherichia coli and Staphylococcus aureus.[10][11] Another way for these bacteria to gain low-level resistance to triclosan is to overexpress FabI.[12] Some bacteria have innate resistance to triclosan at low, bacteriostatic levels, such as Pseudomonas aeruginosa, which possesses multi-drug efflux pumps that 'pump' triclosan out of the cell.[13] Other bacteria, such as some of the Bacillus genus, have alternative FabI genes (FabK) to which triclosan does not bind and hence are less susceptible.

Formation of dioxin in surface water

The use of triclosan in household antibacterial products introduces the chemical to surface waters where it can form dioxins. The dioxin compound that formed when triclosan degraded in sunlight was shown in a study by University of Minnesota researchers not to be of public health concern. Dioxin is not one compound, but a family of compounds of widely ranging toxicity. Of the 210 dioxin and furan family compounds, only 17 are considered to be of public health concern.[14]

Resistance concerns

An article coauthored by Dr. Stuart Levy in the August 6, 1998 issue of Nature[15] warned that triclosan's overuse could cause resistant strains of bacteria to develop, in much the same way that antibiotic-resistant bacterial strains are emerging. In 2003, the Scottish Sunday Herald newspaper reported that some UK supermarkets and other retailers were considering phasing out products containing triclosan.[16]

It has since been shown that the laboratory method used by Dr. Levy was not effective in predicting bacterial resistance for biocides like triclosan.[17] At least seven peer-reviewed and published studies have been conducted demonstrating that triclosan is not significantly associated with bacterial resistance over the short term, including one study coauthored by Dr. Levy.[18]

Some level of triclosan resistance can occur in some microorganisms, but the larger concern is with the potential for cross-resistance or co-resistance to other antimicrobials. Studies investigating this possibility have been limited.[19]

Health concerns

In August 2009, the Canadian Medical Association asked the Canadian government to ban triclosan use in household products under concerns of creating bacterial resistance and producing dangerous side products (chloroform).[20]

Reports have suggested that triclosan can combine with chlorine in tap water to form chloroform gas,[21] which the United States Environmental Protection Agency classifies as a probable human carcinogen. As a result, triclosan was the target of a UK cancer alert, even though the study showed that the amount of chloroform generated was less than amounts often present in chlorinated drinking waters.

Triclosan also reacts with the free chlorine in tap water to produce lesser amounts of other compounds, like 2,4-dichlorophenol.[21] Most of these intermediates convert into dioxins upon exposure to UV radiation (from the sun or other sources). Although small amounts of dioxins are produced, there is a great deal of concern over this effect, because some dioxins are extremely toxic and are very potent endocrine disruptors. They are also chemically very stable, so that they are eliminated from the body very slowly (they can bioaccumulate to dangerous levels), and they persist in the environment for a very long time.

Triclosan is chemically somewhat similar to the dioxin class of compounds. Its production leads to small amounts of residual polychlorinated dioxins, and polychlorinated furans, which are contained in small amounts, in the products that are using it.

A 2006 study concluded that low doses of triclosan act as an endocrine disruptor in the North American bullfrog.[22] The hypothesis proposed is that triclosan blocks the metabolism of thyroid hormone, because it chemically mimics thyroid hormone, and binds to the hormone receptor sites, blocking them, so that normal hormones cannot be used. Triclosan has also been found in both the bile of fish living downstream from waste water processing plants and in human milk.[23] The negative effects of triclosan on the environment and its questionable benefits in toothpastes[24] has led to the Swedish Naturskyddsföreningen to recommend not using triclosan in toothpaste.[25] Another 2009 study demonstrated that triclosan exposure significantly impacts thyroid hormone concentrations in the male juvenile rats.[26]

Triclosan is used in a variety common household products, including soaps, mouthwashes, dish detergents, toothpastes, deodorants, and hand sanitizers.[27] In the United States, manufacturers of products containing triclosan must indicate it on the label.

The American Dental Association published a response to the concerns stemming from the Virginia Tech study [21] stating that the study is not relevant to toothpaste.[28]

The use of triclosan as an additive for plastic production for use in food packages had not been approved by the EC.[29]

Alternatives

A comprehensive analysis from the University of Michigan School of Public Health indicated that plain soaps are just as effective as consumer-grade antibacterial soaps with triclosan in preventing illness and removing bacteria from the hands.[30]

Nonorganic antibiotics and organic biocides are effective alternatives to triclosan, such as silver and copper ions and nanoparticles.[31]

See also

References

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External links

Acridine derivatives
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  1. ↑ 1.0 1.1 "Triclosan: What Consumers Should Know". U S Food and Drug Administratio. 8 April 2010. Retrieved 13 April 2010. 
  2. ↑ Record in the Household Products Database of NLM
  3. ↑ Coia JE, Duc2,8-dichlorodibenzo-p-dioxinkworth GJ, Edwards DI; et al. (2006). "Guidelines for the control and prevention of meticillin-resistant Staphylococcus aureus (MRSA) in healthcare facilities". J. Hosp. Infect. 63 Suppl 1: S1–44. doi:10.1016/j.jhin.2006.01.001. PMID 16581155. 
  4. ↑ Brady LM, Thomson M, Palmer MA, Harkness JL (1990). "Successful control of endemic MRSA in a cardiothoracic surgical unit". Med. J. Aust. 152 (5): 240–5. PMID 2255283. 
  5. ↑ Zafar AB, Butler RC, Reese DJ, Gaydos LA, Mennonna PA (1995). "Use of 0.3% triclosan (Bacti-Stat) to eradicate an outbreak of methicillin-resistant Staphylococcus aureus in a neonatal nursery". American journal of infection control. 23 (3): 200–8. doi:10.1016/0196-6553(95)90042-X. PMID 7677266. 
  6. ↑ 6.0 6.1 6.2 Singer H, Muller S, Tixier C, Pillonel L. (2002). "Triclosan: occurrence and fate of a widely used biocide in the aquatic environment: field measurements in wastewater treatment plants, surface waters, and lake sediments". Environ Sci Technol. 36 (23): 4998–5004. doi:10.1021/es025750i. PMID 12523412. 
  7. ↑ Heidler J, Halden RU. (2007). "Mass balance assessment of triclosan removal during conventional sewage treatment". Chemosphere. 66 (2): 362–369. doi:10.1016/j.chemosphere.2006.04.066. PMID 16766013. 
  8. ↑ Latch DE, Packer JL, Stender BL, VanOverbeke J, Arnold WA, McNeill K (2005). "Aqueous photochemistry of triclosan: formation of 2,4-dichlorophenol, 2,8-dichlorodibenzo-p-dioxin, and oligomerization products". Environ. Toxicol. Chem. 24 (3): 517–25. doi:10.1897/04-243R.1. PMID 15779749. 
  9. ↑ Russell AD (2004). "Whither triclosan?". J. Antimicrob. Chemother. 53 (5): 693–5. doi:10.1093/jac/dkh171. PMID 15073159. 
  10. ↑ Heath RJ, Rubin JR, Holland DR, Zhang E, Snow ME, Rock CO (1999). "Mechanism of triclosan inhibition of bacterial fatty acid synthesis". J. Biol. Chem. 274 (16): 11110–4. doi:10.1074/jbc.274.16.11110. PMID 10196195. 
  11. ↑ Fan F, Yan K, Wallis NG; et al. (2002). "Defining and combating the mechanisms of triclosan resistance in clinical isolates of Staphylococcus aureus". Antimicrob. Agents Chemother. 46 (11): 3343–7. doi:10.1128/AAC.46.11.3343-3347.2002. PMC 128739 Freely accessible. PMID 12384334. 
  12. ↑ Slater-Radosti C, Van Aller G, Greenwood R; et al. (2001). "Biochemical and genetic characterization of the action of triclosan on Staphylococcus aureus". J. Antimicrob. Chemother. 48 (1): 1–6. doi:10.1093/jac/48.1.1. PMID 11418506. 
  13. ↑ Chuanchuen R, Karkhoff-Schweizer RR, Schweizer HP (2003). "High-level triclosan resistance in Pseudomonas aeruginosa is solely a result of efflux". American journal of infection control. 31 (2): 124–7. doi:10.1067/mic.2003.11. PMID 12665747. 
  14. ↑ "Chlorine and Triclosan: The Facts". DioxinFacts.org. 2010-06-03. Retrieved 2010-08-16. 
  15. ↑ McMurry LM, Oethinger M, Levy SB (1998). "Triclosan targets lipid synthesis". Nature. 394 (6693): 531–2. doi:10.1038/28970. PMID 9707111. 
  16. ↑ Supermarkets to ban toxic detergent Rob Edwards, Sunday Herald, 02 November 2003
  17. ↑ McBain AJ, Bartolo RG, Catrenich CE; et al. (2003). "Exposure of sink drain microcosms to triclosan: population dynamics and antimicrobial susceptibility". Appl. Environ. Microbiol. 69 (9): 5433–42. doi:10.1128/AEM.69.9.5433-5442.2003. PMC 194980 Freely accessible. PMID 12957932. 
  18. ↑ Aiello AE, Marshall B, Levy SB, Della-Latta P, Larson E (2004). "Relationship between triclosan and susceptibilities of bacteria isolated from hands in the community". Antimicrob. Agents Chemother. 48 (8): 2973–9. doi:10.1128/AAC.48.8.2973-2979.2004. PMC 478530 Freely accessible. PMID 15273108. 
  19. ↑ Yazdankhah SP, Scheie AA, Høiby EA; et al. (2006). "Triclosan and antimicrobial resistance in bacteria: an overview". Microb. Drug Resist. 12 (2): 83–90. doi:10.1089/mdr.2006.12.83. PMID 16922622. 
  20. ↑ Yang, Jeniffer (2009-08-21). "Experts concerned about dangers of antibacterial products". Globe and Mail. Retrieved 2009-08-25. 
  21. ↑ 21.0 21.1 21.2 Rule KL, Ebbett VR, Vikesland PJ (2005). "Formation of chloroform and chlorinated organics by free-chlorine-mediated oxidation of triclosan". Environ. Sci. Technol. 39 (9): 3176–85. doi:10.1021/es048943. PMID 15926568. 
  22. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  23. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  24. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  25. ↑ Start ~ Naturskyddsföreningen
  26. ↑ "The Effects of Triclosan on Puberty and Thyroid Hormones in Male Wistar Rats - Zorrilla et al. 107 (1): 56 - Toxicological Sciences". Toxsci.oxfordjournals.org. doi:10.1093/toxsci/kfn225. Retrieved 2010-08-16. 
  27. ↑ Triclosan at Household Products Database, U.S. Department of Health and Human Services
  28. ↑ "ADA.org: ADA News: Triclosan study not relevant to toothpaste". ada.org. Retrieved 2010-08-16. 
  29. ↑ COMMISSION DECISION of 19 March 2010 concerning the non-inclusion of 2,4,4’-trichloro-2’-hydroxydiphenyl ether in the Union list of additives which may be used in the manufacture of plastic materials and articles intended to come into contact with foodstuffs under Directive 2002/72/EC 23.3.2010 Official Journal of the European Union
  30. ↑ "Plain soap as effective as antibacterial but without the risk". Retrieved 2007-08-17. 
  31. ↑ Kim, J.S.; et al. (2007). "Antimicrobial effects of silver nanoparticles". Nanomedicine: Nanotechnology, Biology & Medicine. 3 (1): 95–101. doi:10.1016/j.nano.2006.12.001. PMID 17379174. 
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