Epoxiconazole degradation from artificial wetland and forest buffer substrates under flooded conditions

The potential for 14C-epoxiconazole (EPX) degradation in wetland sediments, wetland plants, forest soil and litter was studied under flooded conditions. Mineralization was slow and low (<4% in 177 days). Two major unidentified metabolites were produced among which one was mainly extracted by methanol and had a retention time close to that of EPX. It was suspected to be of similar form to that of the EPX parent compound. A lag-phase was observed for all substrates and mineralization did not reach a plateau. Water-extractable radioactivity did not exceed 8% of the applied amount along the incubation period except for wetland plants (18.8% at day 177). Recovery of initial 14C in methanol extracts decreased with incubation time on average from 100 to 76%. Non-extractable residues (NER) increased up to nearly 18% except for wetland plants which were associated with larger fractions of NER (29.8%) at day 177. Plants’ fresh organic matter seemed to simultaneously enhance NER formation and maintain a relatively high proportion of desorbable mobile residues. A lag-phase kinetic model was proposed. Estimated dissipation half-lives on wetland sediments were less than 65 days and shorter than those estimated in forest soil, wetland plants and forest litter (89–139 days). Reducing conditions did not appear to be favorable to epoxiconazole mineralization although degradation and NER formation occurred. In field conditions, this slow mineralization rate may be compensated by the temporary aerobic conditions created by water level fluctuations.

► Epoxiconazole fate was studied under anoxic conditions in buffer zones substrates. ► Substrates included wetland sediments and plants, and forest soil and litter. ► Mineralization was low, but incomplete degradation led to unidentified metabolites. ► Plants favored both non-extractable and easily desorbable residues. ► A modified lag-phase degradation model fitted well data.