A new theoretical investigation on ·OH initiated oxidation of acephate in the environment: mechanism, kinetics, and toxicity

Abstract

Acephate (O,S-dimethyl acetylphosphoramidothioate) is a typical organophosphorus pesticide used widely in agriculture. It can be released into the atmosphere and water during production and application. In this work, mechanisms in the ·OH initiated degradation of acephate were investigated using quantum chemical methods. Results show that addition, substitution and H-abstraction mechanisms can take place, with the latter being dominant. Moreover, the subsequent reactions of dominant products with O₂ and NO in the atmosphere were considered, as well. The rate constant in the atmosphere and aqueous phase was calculated by transition state theory (TST) with the Wigner tunneling contribution. The total rate constant in the atmosphere and aqueous phase is 7.86 × 10⁻¹⁰ and 1.83 × 10⁻¹² cm³ per molecule per s, respectively, the latter being in accordance with the available experimental value of 1.50 × 10⁻¹² cm³ per molecule per s. Moreover, the ecotoxicity of acephate and degradation products was assessed in fish, daphnia, green algae and rats.