Residue Kinetics and Dietary Risk Assessment of Diazepam and Its Metabolites in Grass Carp ( <i>Ctenopharyngodon idella</i> ): Implications for Aquaculture Safety

ABSTRACT Diazepam (DZP), a benzodiazepine sedative, has been increasingly detected in various aquatic products including fish, shrimp, and crab in recent surveillance studies, raising public health concerns. This study systematically investigates the residue behavior, metabolite profile, and dietary risk of DZP in grass carp ( Ctenopharyngodon idella ) following oral administration at a dose of 500 μg/kg body weight. Concentrations of DZP and its metabolites in plasma and tissues were determined using ultra‐high performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS), and the drug concentration‐time data were fitted using a non‐compartmental model embedded in WinNonLin 6.1 pharmacokinetic software. The results indicate that DZP exhibits prolonged elimination kinetics, with tissue elimination half‐lives ( T 1/2 λz ) ranging from 309.44 to 509.75 h, and residues in skin‐on muscle did not fall below the limit of quantification until 98 days. Metabolite analysis identified nordiazepam as the primary metabolite, with its concentration surpassing that of the parent compound by Day 21 post‐administration, establishing it as a reliable residue marker for DZP in grass carp. The peak human health risk index (HRI) value was 0.392 on Day 4, remaining above the alert threshold (HRI ≥ 0.1) for 21 days, though all values remained below the safety limit (HRI &lt; 1). These findings provide critical data to support the regulation of aquaculture practices and the assessment of dietary exposure risks associated with DZP‐contaminated aquatic products.