title: Aqueous photochemistry of triclosan: formation of 2,4-dichlorophenol, 2,8-dichlorodibenzo-p-dioxin, and oligomerization products.
abstract: The photochemical fate of the antimicrobial agent triclosan is presented. Experiments performed in both natural and buffered deionized water show that triclosan rapidly photodegrades by direct photolysis (t(1/2) = 5 h, pH 8, noon summer sunlight, 45 degrees N latitude). Both 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) and 2,4-dichlorophenol (2,4-DCP) are produced. The 2,8-DCDD and 2,4-DCP also are photolabile and, thus, are intermediates. The yields for 2,8-DCDD and 2,4-DCP ranged from 3 to 12% depending on the conditions employed. When triclosan is photolyzed in the presence of Suwannee River (GA, USA) fulvic acid, a portion of the initial mass is recovered as insoluble material. Based on experiments in which the formation of insoluble material was monitored with photolysis time, it is postulated that photolysis in natural waters leads to some of the triclosan being coupled to humic matter. Triclosan also reacts rapidly with both singlet oxygen (k(rxn) = 1.07 +/- 0.03 x 10(8) M(-1) s(-1) in water of pH 10) and hydroxyl radical (k(*OH) = 5.4 +/- 0.3 X 10(9) M(-1)(s-1). Indirect photolysis pathways, however, are not expected to be important because of low steady-state concentrations of reactive oxygen species in natural waters and the efficiency of the direct photolysis of triclosan.
authors.affiliation: Department of Chemistry, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, USA.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Latch
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Packer
authors.forename: Brian L
authors.initials: BL
authors.lastname: Stender
authors.forename: Jennifer
authors.initials: J
authors.lastname: VanOverbeke
authors.forename: William A
authors.initials: WA
authors.lastname: Arnold
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
mesh_terms: D000891:Anti-Infective Agents, Local / Q000737:chemistry*; D001578:Benzopyrans / Q000737:chemistry; D002733:Chlorophenols / Q000737:chemistry; D004147:Dioxins / Q000737:chemistry; D005845:Georgia; D017665:Hydroxyl Radical / Q000737:chemistry; D008910:Minnesota; D010782:Photolysis; D045483:Rivers / Q000737:chemistry; D012621:Seasons; D026082:Singlet Oxygen / Q000737:chemistry; D013472:Sunlight; D014260:Triclosan / Q000737:chemistry*
chemical_list: D000891:Anti-Infective Agents, Local; D001578:Benzopyrans; D002733:Chlorophenols; D004147:Dioxins; D026082:Singlet Oxygen; D017665:Hydroxyl Radical; D014260:Triclosan; C068993:2,8-dichlorodibenzo-4-dioxin; C004762:2,4-dichlorophenol; C005023:fulvic acid