Laboratory Assessment of ¹⁴C-Phenyl Metsulfuron-Methyl Degradation in an Oil Palm Plantation Soil

The ¹⁴C-phenyl metsulfuron-methyl is a selective systemic sulfonylurea herbicide. Degradation studies in soils are esse tial for the evaluation of the persistence of pesticides and their breakdown products. The objective of this study was to investigate the degradation of metsulfuron-methyl in an oil palm plantation soil under laboratory conditions. The soil used was both sterilised and non-sterilised soil in order to observe the involvement of soil microbes. The estimated DT₅₀ and DT₉₀ values of metsulfuron-methyl in a nonsterile system were approximately 13 and 44 days, whereas in sterilised soil, the DT₅₀ and DT₉₀ were 31 and 70 days, respectively. The principal degradation product after 60 days is CO₂. The higher cumulative ¹⁴CO₂ in ¹⁴C-phenyl in the non-sterilised soil compared to that in the sterile system suggests that bi logical degradation by soil micro-organisms significantly contribute to the dissipation of the compound. In some the major routes of degradation are O-demethylation, sulfonylurea bridge cleavage and triazine ring-opened. In vitro study in order to identify the microbes involve in the degradation of the compound should be carried out in the future study. (author)