Degradation of the herbicide [14C]-diclofop-methyl in soil under different conditions

The degradation of the herbicide diclofop-methyl, ( ± )-methyl 2-4-(2,4-dichloro-phenoxy)phenoxy]propionate, was investigated in two agricultural soils under aerobic and anaerobic conditions. Using two differently labelled forms of ¹⁴C]-diclofop-methyl the qualitative as well as the quantitative formation of extractable metabolites was followed for 64 days. The mineralisation of the uniformly labelled aromatic rings was pursued by monitoring the ¹⁴CO₂ generated for 25 weeks. As a first step of the degradation a very rapid hydrolysis of the ester bond was detected under all conditions. Diclofop, the corresponding substituted propionic acid formed, was extensively degraded under aerobic conditions, the final product being ¹⁴CO₂. As an intermediate, a compound later identified by GLC/MS to be 4-(2,4-dichlorophenoxy)phenol, was found in the extracts. Furthermore, traces of six other unknown metabolites were detected. Under anaerobic conditions the degradation proceeded to a small extent. At most 3% of the applied radioactivity was accounted for by the degradation product 4-(2,4-dichlorophenoxy)phenol. No other metabolite, including ¹⁴CO₂, was observed, implying lack of any further degradation.