Acetochlor mineralization and fate of its two major metabolites in two soils under laboratory conditions

The degradation of the herbicide acetochlor, in a neoluvisol and in a calcosol were studied as a function of depth (0–25 cm and 25–50 cm) and temperature (25 °C and 15 °C) under controlled laboratory conditions during 58 and 90 days, respectively. The surface and sub-surface soil samples were respectively spiked with 1 and 0.01 mg kg −1 of 14C-acetochlor, the concentrations observed in previous field monitoring. The half-lives (DT 50) varied from 1.4 to 14.9 days depending on the soil, temperature and applied concentration. The maximal mineralization (24%) was observed for the surface calcosol at 25 °C. The comparison of results obtained for sterilized and non-sterilized soils, the decrease of DT 50 with the increase of temperature, the shape of CO 2 emissions and the increase of number of aerobic endogenous microflora through the experiment suggested that biological process are dominant in degradation. A particular attention was paid to the formation and dissipation of metabolites ESA (ethanesulphonic acid) and OA (oxanilic acid) during the whole experiment. At 25 °C, ESA and OA were observed after three days, but as ESA concentration decreased over time in surface calcosol, it remained constant in surface neoluvisol. A difference in ESA/OA ratio depends on the soil with a predominance of OA in surface neoluvisol and a disappearance of OA in surface calcosol.