Identification and Quantification of Dimethachlon Degradation Products in Soils and Their Effects on Soil Enzyme Activities

In this study, high-performance liquid chromatography–high-resolution mass spectrometry (HPLC–HRMS, Q-Exactive Orbitrap) and Compound Discoverer 3.3 were used to screen dimethachlon degradation products in soils. Four metabolites 4-(3,5-dichloroanilino)-4-oxobutanoic acid (DCBAA), 3,5-dichloroaniline (3,5-DCA), succinic acid, and muconic acid were confirmed by primary and secondary ion mass spectrometry comparisons between standards and samples. A quantitative analysis method of dimethachlon residues and four metabolites in soils was developed using HPLC–HRMS. Dimethachlon degradation in agricultural soil indoor unsterilized, sterilized, and field environments in three typical areas was measured. Dimethachlon degraded fast with a half-life of less than 1 day in three nonsterile soils. The maximum DCBAA and 3,5-DCA residues during degradation could reach 22.5–35.2% of the initial concentration of the parent dimethachlon. The metabolite DCBAA had a greater impact on soil enzyme activity than the parent dimethachlon.