CHEMICAL OR MICROBIAL-DEGRADATION OF SULFONYLUREA HERBICIDES IN SOIL .1. SULFOMETURON METHYL

The rates of degradation of sulfometuron methyl in a soil and in aqueous solution at the same pH were measured at different temperatures. The Arrhenius relationship was verified between 20-degrees-C and 75-degrees-C. The calculated activation energy in soil and in solution was 94 kJ mol-2 and 117 kJ mol-1, respectively. From the fact that the Arrhenius relationship is followed up to 70-degrees-C, it is proposed that the mechanism of degradation in the soil is chemical. Analysis of the metabolites formed in sterile and non-sterile soil was performed using sulfometuron methyl labelled with C-14 in the pyrimidine ring. In both soils the main metabolite isolated was 2-amino-4,6-dimethylpyrimidine. No significant difference has been observed between sterile and non-sterile soils.