OH/O3-initiated transformation of primidone in AOPs based on the theoretical calculations: Mechanisms, kinetics, and eco-toxicity assessments

Abstract

Primidone (PMD), as the first-generation anticonvulsant, is attracting considerable attention due to its extensive persistence in aqueous environments. In this paper, the aquatic transformation mechanisms, kinetics, and eco-toxicity of PMD induced by OH/O3 have been investigated through density functional theory (DFT). The results indicated that the H atom of -CH2- group (H8), which is located on the pyrimidine ring, is more vulnerable to be abstracted by OH radicals. This led to the most dominant intermediate IM8, which could be converted into the primary products (P3, P4, P5, P8, and P16). Moreover, the OH-addition channels were also considered, where the routes to form IM12 and IM16 play important roles. In terms of the reaction between PMD and O3, the cyclo-addition and subsequent degradation pathway were researched, generating the main ozonation compound P35. In addition, the calculated ktotal of PMD reacting with OH radicals and O3 at 298 K were 2.81 × 109 and 2.55 × 10−1 M−1 s−1 respectively, indicating OH radicals represent higher universality than O3. The half-lives of PMD oxidized by OH radicals range from 0.19 to 30.12 s, while the values of O3-initiated reactions are within the scope of 0.05–2.15 h in the AOPs. The eco-toxicities of the primary degradation products, di-ketone compounds (P5 and P8), to aquatic organisms have decreased to harmless, while the developmental perniciousness of several metabolites (P3, P7, P9, and P12) still remain. This work will provide a deep insight into the behavior of PMD mineralization for the first time at the computational molecule.