Analysis Of The Photodegradation Products Of Triclosan

Triclosan, 5-chloro-2-(2,4-dichlorophenoxy) phenol, is a popular antibacterial agent which has evoked a great deal concerns on its environmental fate due to its widely applications. Determination of the triclosan content in both toothpastes and hand lotions was conducted by using high performance liquid chromatography. Meanwhile, the potential unsafe compounds were analysed by comparing with the retention time of the standards of dibenzo-p-dioxins. Standards addition method was chosen as a detection means. 28 toothpastes in the market were examined in this paper and it was found that the contents of triclosan in every toothpaste sample were different, even for the same brand sample. The results also revealed that the contents of triclosan in all the tested samples are in accordance with the international standard. After examination of the potential harzardous materials related with the triclosan, no dibenzo-p-dioxins or other chlorophenols were detected in toothpaste samples. To exam the potential effluent of chlorophenols into environment, the water samples of Taihu lake were analysed after precipitation, filtration and concentration, no triclosan or other related chlorophenols were detectable.On the basis of the above work, the processes of the photodegradation and the influence factors were also studied. The degradation of triclosan under UVB irradiation followed first-order kinetics. There were 7 photoproducts produced at pH8.7, and these photoproducts exhibit some extent of stability to further photodegradation. It was also found that triclosan is more liable to photodegradation in aqueous solution when compared with that of in organic solvent, such as ethanol. The effect of surfactants on the photodegradation was also investigated. In the presence of surfactants, triclosan was more resistant to photodegradation compared with their absence. Non-ionic surfactant, Triton X-100, exhibits strongest shielding effect on the triclosan photodegradation among the surfactants tested. And this effect was more pronounced when the photodegradation was carried out at pH 8.7 comparing with that at pH10.5. In general, the shielding effect is increasing with the increase of surfactant concentrations. After considering surfactant types, pH and concentrations, it was concluded the surfactant influences were dependant on the following aspects: the first was types of surfactant. Non-ion surfactant has more protective or shielding effects for non-polar compounds; the second was the structure of the surfactant. The one which include the phenyl composition in its structure adsorb the ultraviolet radiation during the degradation process would have more pronounced shielding effects on the the photodegradation. The third factor is that the surfactant effect also depends on the forms of a molecule, i.e., the shielding effect of a surfactant on a molecule and its effectiveness is a function of solution pH, as different pH would lead to a different extent of a triclosan ionization, hence the charge possess by it.Finally, photodegradation mechanism of the triclosan was investigated. The photoproducts was analysed by the LC-MS and GC-MS. 2,4-dichlorophenol and 2,8-DCDD was confirmed by matching with the standards of the corresponding materials. The photopolymerizaiton products was analysed by the LC-MS. The numbers of the chlorine atom in photopolyerization products was estimated by the ratio of the two isotopes of chlorine atom, and hence the structures of the photoproducts could be duduced. All of the polymerized products were dimmers or trimers. Dechlorination takes place during the photo reaction process. For example, 5-chloro-2- (4-dichlorophenoxy) phenol was a result of dechlorination. Four main routes were proposed in the triclsoan photo-reaction process under UVB irradiation, namely homolytic scission of ether bond, dechlorination, ring closure and photo-polymerization.