Researchers from Guangzhou Institute of Geochemistry, Chinese Academy of Sciences have firstly achieved the absolute bimolecular rate constants of propyl paraben (PPB) with e aq- and HO• at the 109 M-1 s-1 by using pulse radiolysis, indicating that PPB can be easily oxidized by HO• and reduced by e aq- in water. In addition, the obtained half-life of photocatalytic degradation of PPB (3.5-76.2 min) revealed that PPB can be effectively degraded during AOPs, and oxidative species, particularly HO•, were the most important reactive oxygen species mediating photocatalytic degradation of PPB.

Based on absolute bimolecular rate constants as well as experimental and calculated UV/Vis absorption spectra of PPB and transient intermediates, it is found that HO•-addition or H-abstraction reactions are the two main initial steps. Toxic evaluation showed that the estrogenic activity of PPB can be effectively detoxified, while the acute toxicity at three trophic levels first increased slowly and then decreased rapidly as the total organic carbon decreased during the photocatalytic degradation. This implied that the treatment time of AOPs should be determined carefully for safe water.

The obtained results about initial reaction and reaction pathways in AOPs could be used to tentatively predict the fate of other ECs with a similar structure of PPB. In addition, the results suggested that the toxicity of intermediates was relied on the initial reaction step of PPB, and the transformation mechanisms as well as the fates of these ECs in water are depending on not only AOPs system but also ECs structure.

The relative results were published in Environmental Science & Technology. (Fang, H.S.; Gao, Y.P.; Li, G.Y.; An, J.B.; Wong, P.-K.; Fu, H.Y.; Yao, S.D.; Nie, X.P.; An, T.C. Advanced Oxidation Kinetics and Mechanism of Preservative Propylparaben Degradation in Aqueous Suspension of TiO₂ and Risk Assessment of Its Degradation Products. Environmental Science & Technology 2013, 47, (6), 2704-2712. doi: 10.1021/es304898r)