Hydroxylated polyhalogenated diphenyl ethers (HO-PXDEs) are widely detected environmental endocrine disruptors. Environmental phototransformation of HO-PXDEs may lead to the formation of dioxins. However, the photochemical reaction mechanisms of these compounds has not been fully elucidated. In this study, the phototransformation pathways of HO-PXDEs were explored with triclosan and 2'-HO-BDE-28 as model compounds. Their photolysis rate constants (k), quantum yields (Φ), relative light absorptions (Ar) and dioxin formation yields for both the neutral and anionic forms were determined. Indirect photolysis and the nature of excited states involved in the photolysis were explored. Results showed that the k value of 2'-HO-BDE-28 is higher than that of triclosan at pH = 4 solutions for the higher Ar value of 2'-HO-BDE-28; the k value of triclosan was higher than that of 2'-HO-BDE-28 at pH = 11 solutions due to the higher Φ value of triclosan. 2,8-dichlorodibenzodioxin (2,8-DCDD) and 2,7/2,8-dibromodibenzodioxin (2,7/2,8-DBDD) were detected in the direct photolysis of anionic forms of triclosan and 2'-HO-BDE-28. The formation yield of 2,8-DCDD (2.7%) is higher than that of 2,7/2,8-DBDD (1.9%). The direct photolysis of both triclosan and 2'-HO-BDE-28 was mainly through their excited singlet states, leading to the formation of dioxins and other photoproducts. Self-sensitized photolysis (photo-oxidation by hydroxyl radicals (·OH) and singlet oxygen (1O2)) was proved to be involved in the phototransformation. ·OH and 1O2 can be formed through energy and electron transfer from excited states of the two compounds to 3O2. The mechanism understanding is important for assessing the photochemical fate of HO-PXDEs in the environment.

Insights into photochemical transformation pathways of triclosan and 2'-HO-BDE-28

249th National Meeting (2015)

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