Transformation characteristics of typical antidepressants in UV-advanced oxidation processes

Antidepressants, as psychoactive pharmaceuticals and personal care products (PPCPs), have been frequently detected in the environment; however, studies on their photochemical transformation remain limited. Ultraviolet/hydrogen peroxide (UV/H₂O₂) and UV/peroxydisulfate (UV/PDS), which are representative advanced oxidation processes (AOPs) for generating hydroxyl radicals (^•OH) and sulfate radicals (SO₄^•-), have been widely employed and are theoretically effective for eliminating antidepressants. This study comprehensively investigated the direct photolysis of six typical antidepressants at 254 nm UV and the degradation behaviors under UV/H₂O₂ and UV/PDS processes. The results revealed an 88.9-fold variation in direct photolysis rates among different antidepressants under UV irradiation. Both UV-AOPs significantly enhanced the degradation of all target antidepressants, with pseudo-first-order rate constants increased by 2.47- to 105.19- fold. Furthermore, most antidepressants exhibited lower second-order reaction rate constants with SO₄^•- than with ^•OH. Notably, the halogenated antidepressants underwent effective dehalogenation during degradation, and the dehalogenation ability of UV/PDS is stronger than that of UV/H₂O₂, but it may also bring new risks (such as a higher potential for generating trifluoroacetic acid). The degradation pathways under both UV/H₂O₂ and UV/PDS were similar, predominantly involving dealkylation and hydroxylation. Most intermediates showed reduced acute toxicity and bioaccumulation potential, though long-term risks (e.g., TFA) remain unclear. Overall, this study initially revealed the degradation characteristics and proposed pathways of typical antidepressants treated with UV-AOPs. These findings contribute to a better understanding of the photochemical behavior and fate of antidepressants in aquatic environments and could facilitate the development of efficient and novel AOPs for their removal.