Theoretical insights into the degradation of swep by hydroxyl radicals in atmosphere and water environment: Mechanisms, kinetics and toxicity

Abstract

As an excellent conductive herbicide, swep is widely used in weed removal. Its remaining in atmosphere and water can not only contaminate the environment but also pose a threat to human health. This work presented a systematic theoretical study of HO•-mediated degradation mechanisms and kinetics of swep in atmosphere and water environment. HO•-addition reaction was the dominant reaction type and the main degradation products N-(3-chloro-4-hydroxyphenyl)carbamate (P2), N-(3,4-chloro-6-hydroxyphenyl)carbamate (P3) and N-(3,4-chloro-2-hydroxyphenyl)carbamate (P11) were in good agreement with the experimental results. The total rate constants of swep with HO• were determined to be 3.37 × 10−12 and 7.73 × 10−12 cm3 molecule−1 s−1 (at 298 K) in atmosphere and water environment, respectively. As an excellent adsorbent and photocatalyst, zinc oxide (ZnO) was selected to study the adsorption and catalytic degradation mechanism of swep. The adsorption configuration of (ZnO)n clusters with swep was most stable when n = 6. The adsorption of (ZnO)6 cluster was more favorable to the H-atom abstraction reaction. The toxicities of swep and its degradation products to aquatic organisms were predicted. The degradation of swep induced by HO• was beneficial to the survival of aquatic organisms. This work would provide a comprehensive theoretical basis for understanding the degradation behavior of organic pollutants.