Triclosan + Chlorinated Water = Chloroform
Triclosan: the news continues to get worse
Compiled by Melissa Kaplan
Formation of chloroform
and chlorinated organics by free-chlorine-mediated oxidation of triclosan.
The widely used antimicrobial agent triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) readily reacts with free chlorine under drinking water treatment conditions. Overall second-order kinetics were observed, first-order in free chlorine and first-order in triclosan. Over the pH range of 4-11.5, the kinetics were pH sensitive as a result of the pH dependent speciation of both triclosan and free chlorine. Using a Marquardt-Levenberg routine, it was determined that this pH effect indicates that the dominant reaction in this system is between the ionized phenolate form of triclosan and hypochlorous acid (HOCl). The overall second-order rate coefficient was determined to be kArO- = 5.40 (+/- 1.82) x 10(3) M(-1) s(-1). Three chlorophenoxyphenols and two chlorophenols were identified by gas chromatographic-mass spectroscopic analysis. The chlorophenoxyphenol compounds include two monochlorinated triclosan derivatives (5,6-dichloro-2-(2,4-dichlorophenoy)phenol and 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol) and one dichlorinated derivative (4,5,6-trichloro-(2,4-dichlorophenoxy)phenol); these species form via bimolecular electrophilic substitution of triclosan. 2,4-Dichlorophenol was detected under all reaction conditions and forms via ether cleavage of triclosan. In experiments with excess free chlorine, 2,4,6-trichlorophenol was formed via electrophilic substitution of 2,4-dichlorophenol. Chloroform formation was observed when an excess of free chlorine was present. A Hammett-type linear free-energy relationship (LFER) using Brown-Okamoto parameters (sigma+) was established to correlate the reactivity of HOCI and the phenolate forms of triclosan and other chlorophenols (log kArO- = -(10.7 +/- 2.2)Sigmasigma(+)o,m,p + 4.43). This LFER was used to obtain estimates of rate coefficients describing the reactivity of the intermediates 5,6-dichloro-2-(2,4-dichlorophenoy)phenol (kArO- approximately equal to 6 x 10(2)), 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol (kArO- approximately equal to 3 x 10(2)), and 4,5,6-trichloro-(2,4-dichlorophenoxy)phenol (kArO- approximately equal to 4 x 10(1)).
PMID: 15926568 [PubMed - in process]
Dozens of toothpastes sold at supermarkets are at the centre of a cancer alert today. Anti-bacterial cleaning products, including dishwashing liquid and handwash, are also affected.
Researchers have discovered that triclosan, a chemical in the products, can react with water to produce chloroform gas. If inhaled in large enough quantities, chloroform can cause depression, liver problems and, in some cases, cancer.An Evening Standard investigation found dozens of products on supermarket shelves containing the chemical, from brand names including Colgate, Aquafresh, Dentyl and Sensodyne.
Marks & Spencer confirmed today it was removing products containing triclosan from all its stores and has been working with Greenpeace to develop alternative products.
Asda said it was investigating the problem and would be urgently talking to its suppliers.
Giles Watson, a toxicology expert at wildlife charity WWF, warned that the long-term effects of exposure to chloroform were still unknown and advised consumers to check the bottles before buying products.
"These products produce low levels of chloroform, but that adds up over time. The amount of gas formed is very low but I think the key thing is that we just don't know what the effects are. However, manufacturers do have to list triclosan on their ingredients, so if consumers are worried the best advice is to avoid products with the chemical."
A Tesco spokesman said: "We do not use triclosan in any of our own-brand products, apart from one anti-bacterial handwash, which is being reformulated, and our toothpaste. We believe that triclosan is a very effective ingredient in toothpaste as it helps fight gum disease and improve overall oral care."
The Department of Trade and Industry said use of triclosan was tightly controlled under EU laws brought in last year, but that they were under constant review.
Researchers in the US found that the chlorine added to water in Britain reacted with triclosan to produce chloroform-gas. They found that it was possible for the chloroform produced when soap containing the chemical mixes with chlorinated water to be absorbed through the skin or inhaled.
Professor Peter Vikesland, of Virginia Tech University, who carried out the research, said: "This is the first work that we know of that suggests that consumer products, such as antimicrobial soap, can produce significant quantities of chloroform." He has called for governments around the world to regulate the chemical more closely.
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