Bioaccumulation and Biotransformation of Triazole Pesticides in Rice (Oryza sativa L.): Quantitative Structure–Activity Relationship, Metabolic Pathways, and Toxicity Assessment

Root uptake is a primary pathway for pesticides to enter the plants; however, their uptake mechanisms and biotransformation behaviors are still lacking. Herein, the root uptake and biotransformation behaviors of 21 triazole fungicides in rice plants (Oryza sativa L.) by hydroponic experiments were investigated. The uptake of triazoles in rice roots may directly and mainly originate from adsorption in the root surface, not directly dominated by nutrient solution. A QSAR model revealed that the molecular descriptors related to log K_ow and molecular polarizability (e.g., ALogP and ATSC6p) were closely associated with the bioaccumulation of triazole fungicides. Twenty-six metabolites of six typical triazole pesticides were identified, and six among them were determined for the first time. The toxicity prediction by Ecological Structure Activity Relationships Predictive Model (ECOSAR) software indicated that biotransformation products (e.g., methylation products) may exhibit a higher toxicity. Therefore, the ecological risk posed by pesticide biotransformation products should be a concern, which needs further investigation.