Degradation and detoxification of acetochlor in soils treated by organic and thiosulfate amendments

This work investigated the degradation and detoxification of acetochlor in a soil amended with an organic fertilizer or sodium thiosulfate (STS). Over an incubation period of 28 d, the residual acetochlor was measured, soil dehydrogenase activity was determined, and major degradates were identified. Results show that high-concentration acetochlor was persistent in the soil, as indicated by the depression in soil dehydrogenase activity. When the soil was amended with the organic fertilizer, the soil dehydrogenase activity was stimulated by supplemented nutrients, which resulted in a higher degradation of acetochlor. While STS did not significantly stimulate the soil dehydrogenase activity, acetochlor degraded more rapidly in STS-amended soil than in organic-amended soil. The Wright-Hobbie plots show that the influence of initial acetochlor concentration on degradation was dependent on the amendments. While the organic amendment resulted in the same degradate of acetochlor ethanesulfonic acid as in unamended soil, the STS amendment produced dechlorinated acetochlor thiosulfonic acid. The degradation of acetochlor in organic- and STS-amended soils thus occurred via different mechanisms. Further tests show that both degradates were less toxic to green algae than acetochlor. Both organic and STS amendments thus effectively degrade and detoxify acetochlor in soils.