Degradation studies of dimethachlor in soils and water by UHPLC‐HRMS: putative elucidation of unknown metabolites

BACKGROUND The analytical control of the presence of dimethachlor and its metabolites in environmental samples, such as water and soils, is a main concern. Degradation of this pesticide has been evaluated in two types of soils and two different water conditions at two concentration levels. For that purpose, a new liquid chromatography‐mass spectrometry method has been developed and putative identification of new metabolites has been performed. RESULTS An analytical method based on ultra‐high‐performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC‐Orbitrap‐MS) was developed to monitor the degradation of dimethachlor in environmental samples (water and soils). The degradation of dimethachlor in soils and groundwater samples has been monitored from 1 to 110 days after application of a plant protection product at two doses. Concentration of the parent compound slowly decreased in both matrices. DT50 values ranged from 40 to 70 days. Some metabolites were detected in the commercial product and in the samples one day after the application of the plant protection product. In addition, three new metabolites were putatively identified during dimethachlor degradation by untargeted analysis. CONCLUSION In this study, the degradation of dimethachlor into its metabolites has been studied in soils and water, using a UHPLC‐Orbitrap‐MS validated method. A putative elucidation of new metabolites of dimethachlor has been carried out applying HRMS and software tools. Degradation results allowed for understanding the behavior of dimethachlor in soils and water, and provided information regarding the possible risk of this pesticide and its metabolites to the ecosystem. © 2019 Society of Chemical Industry Degradation of dimethachlor was evaluated in soils and water, detecting metabolites in incurred samples. Putative elucidation was performed using HRMS and software tools, detecting new possible metabolites of dimethachlor.