Degradation of prosulfocarb by hydroxyl radicals in gas and aqueous phase: Mechanisms, kinetics and toxicity

Prosulfocarb (PSC) is a thiocarbamate herbicide mainly used in winter cereals and a relevant aerosol precursor under OH radicals (center dot OH) photooxidation conditions. We investigated the environmental risks, mechanisms, kinetics and products for the PSC with center dot OH by employing theoretical chemical calculations. Two reaction types of H-abstraction and center dot OH-addition reactions were taken into account. Whether in the atmosphere or aqueous particles, the most favorable pathway was the H-abstraction in the N-alkyl groups close to nitrogen atom. Subsequent reactions of primary intermediates were considered at different conditions. The total rate constants were determined as 2.62 x 10-10 cm(3) molecule-1 s-1 and 4.96 x 10-11 cm(3) molecule-1 s-1 at 298 K in atmosphere and aqueous particles, respectively. In natural water with the center dot OH concentration of 10-15-10-18 mol 1-1, the half-lives (t1/2) of PSC in the center dot OH-initiated reactions were calculated as t(1/2) = 2.40 x 10(4)-2.40 x 10(7) s. With regard to the influence on human health and the ecosystem, oxidized products of PSC were estimated to be mutagenicity negative and had no obvious bioaccumulation potential. The aquatic toxicity of PSC and its degradation products was evaluated and the assessment results showed that the degradation of PSC was a toxicityreduced process but they were still at toxic and harmful levels.