Identification of dimethachlon metabolites and dissipation behavior, processing factor and risk assessment of dimethachlon in rapeseed

Pesticides and their transformation products are found in raw agricultural and processed food products, posing risks to human health. Therefore, a thorough investigation of dimethachlon’s dissipation, metabolites, residue levels in crops, and changes during food processing is essential for an accurate dietary risk assessment. This study identified two metabolites, 4-(3,5-dichloroanilino)-4- oxobutanoic acid (DCBAA) and 3,5-dichloroaniline (3,5-DCA), formed from dimethachlon in crops under field conditions. A precise and sensitive analytical method was developed to detect dimethachlon, DCBAA, and 3,5-DCA in rapeseed pods, seeds, and oil. The half-lives of dimethachlon in rapeseed pods at two sites ranged from 1.61 to 1.67 days. During degradation, the maximum residue levels of DCBAA and 3,5-DCA in rapeseed pods reached 38.59 % and 3.47 % of the initial parent compound concentration, respectively. At harvest (day 10), final dimethachlon residues in rapeseed were 0.11 mg/kg and 0.27 mg/kg. Processing rapeseed into oil through sun-drying and stir-frying reduced dimethachlon residues, with processing factors (PF) of 0.69 and 0.64, respectively. However, pressing the seeds concentrated dimethachlon in the oil, with a PF of 1.92. Notably, DCBAA tended to concentrate during sun-drying but decreased during stir-frying and pressing. Supervised trials indicated that dimethachlon residues in rapeseed posed no long-term dietary risks.