Study on the residual dynamics of diazepam in freshwater fish of Zhejiang, China and its implications for human health.

This study provides an in-depth evaluation of diazepam (DZP) and its metabolites in freshwater fish from Zhejiang Province, China, during 2020-2024, with a focus on contamination trends, source attribution, bioaccumulation behavior, and potential human health risks. The results reveal a significant upward trend in DZP detection, rising from 0.33 % to 4.67 %, accompanied by a 75 % increase in mean residue concentrations-from 2.31 ± 1.26 μg/kg to 4.04 ± 7.65 μg/kg-and a maximum concentration reaching 76.04 μg/kg. Recreational fishing areas exhibited the most severe contamination, with crucian carp identified as the most heavily affected species. Among DZP metabolites, nordiazepam (NZP) exhibited stable detection rates (1.20-1.37 %), while oxazepam and temazepam were rarely detected, suggesting selective metabolic pathways. Source analysis identified bait as the dominant contributor, with DZP levels reaching up to 1.10 × 105 μg/kg. Crucian carp exhibited the highest bioaccumulation factor (BCF = 1238.60), reinforcing their heightened susceptibility. Molecular docking analyses revealed species-specific binding affinities of DZP and NZP to fish GABA receptors, providing mechanistic insight into observed residue patterns. Health risk assessments indicated low average dietary exposure for adults, whereas under extreme exposure scenarios, hazard quotients (HQ) for children approached the threshold of concern (HQ = 0.49). These findings underscore the urgent need for strengthened regulation of bait quality and contamination control in recreational fishing areas to mitigate future food safety risks.