Theoretical investigation on the transformation of ketamine initiated by ⋅OH/SO4−⋅ in aqueous solution: Mechanisms, kinetics and ecotoxicity assessment

Abstract

Ketamine (KET), as an analgesic medicine, has raised considerable attention due to its widespread existence and potential environmental hazards. This study researched the transformation mechanisms, kinetics, and potential ecology risks of KET degradation initiated by ⋅OH/SO4−⋅ through density functional theory (DFT). The calculation results show that the H15 atom belongs to the -CH3 group is more likely to be extracted by ⋅OH or SO4−⋅, generating the most active dehydrogenated radical intermediate IM21, which could further transform into the principal products (P1, P2, P3, P5, P6, and P8) in the aquatic environment. Furthermore, the subsequent degradation pathways of other active intermediates IM2, IM16, and IM19 were also considered. At 298 K, the calculated ktotal of KET reacting with ⋅OH and SO4−⋅ are 1.34 × 1010 and 1.11 × 1010 M−1 s−1, respectively, demonstrating that the ⋅OH shows slightly higher initiation performance than SO4−⋅. In terms of the half-lives, the values in ⋅OH-initiated AOPs are at the range of 0.05–5.75 s, while the half-lives of KET reaction oxidized by SO4−⋅ range from 0.01 to 437.03 d in 273–313 K. Based on the toxicity evaluation, the majority of degradation products present toxicity decreasing, but some of them remain at toxic or very toxic levels, such as P1, P3, P13, and P20. In addition, the accumulative effects, developmental toxicity, mutagenicity, and carcinogenicity of multiple transformation products increase compared with parent KET. This work could contribute to enhancing the comprehension of KET mineralization in liquid ecosystems and establish a theoretical basis for prospective industrial applications.