Soil Metabolism of [14C]MRC-04 under Aerobic and Aerobic Flooded and Anaerobic Conditions

MRC-04 (5-(((2,6-difluorobenzyl)oxy)methyl)-5-methyl-3-(o-tolyl)-4,5-dihydroisoxazole), is an analogue of a new turf herbicide methiozolin, is a herbicide candidate with a potent herbicidal activity to various paddy weeds, especially against susceptible and ALS-resistant barnyardgrass. The fate of MRC-04 was investigated in soil under an aerobic, aerobic flooded, and anaerobic condition using [benzyl-14C]MRC-04, describing the mass balance, the degradation pattern and formation of metabolites. Overall mass balance was in the range of 90.2-103.3% of the applied in all the soil conditions. MRC-04 steadily degraded to 23.6 and 11.7% of the applied at 120 and 60 days, and the estimated half-life was 63.0 and 17.9 days in the soil under the aerobic and aerobic flooded conditions, respectively. However, the half-life could not be calculated in the soil under the anaerobic condition because MRC-04 degradation was limited. Carbon dioxide increased to 24.1, 30.9 and 13.7% of the applied, and non-extractable residue increased to 35.9, 11.6, and 15.3% at 120, 60, and 120 days in the soil under the aerobic, aerobic flooded, and anaerobic conditions, respectively. No significant volatile compound was detected during this study. Three major metabolites were detected in the soil under aerobic flooded condition and identified as 2,6-difluorobenzoic acid, 4-((2,6-difluorobenzyl)oxy)-3- hydroxy-3-methyl-1-(o-tolyl)butan-1-one and 1-((2,6-difluorobenzyl)oxy)propan-2-ol. Conclusively, MRC-04 was shown to undergo fast degradation in aerobic conditions, especially when flooded, but not in an anaerobic condition in soil. KCI Citation Count: 0