Occurrence and ecological risk assessment of diazepam and its metabolites in aquaculture environment in the Pearl River Delta region

Diazepam (DIAZ), a widely prescribed benzodiazepine for insomnia and anxiety, has been frequently detected in aquatic ecosystems, raising concerns about potential impacts on human and animal health. To investigate its environmental presence, water and sediment samples were collected from 187 aquaculture ponds across the Pearl River Delta, China. The concentrations of DIAZ and its metabolites—nordazepam (NDZ), oxazepam (OXZ), and temazepam (TEM)—were determined using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). Detection frequencies in water ranged from 0.535 % to 58.8 %, with concentrations from below detection (nd) to 392 ng·L −1 , whereas in sediments, frequencies ranged from 1.07 % to 35.8 %, with levels from nd to 1.66 μg·kg −1 . Marked spatial variability was evident, with aquaculture ponds in Foshan (FS) exhibiting the highest DIAZ concentration (392 ng·L −1 ), while Zhongshan (ZS) displayed higher detection frequencies but lower concentrations. Fish ponds contained significantly greater cumulative concentrations of DIAZ and its metabolites compared with shrimp ponds. Strong positive correlations were identified between DIAZ in water and DIAZ and NDZ in sediments. Similarly, NDZ in water was strongly correlated with NDZ and DIAZ in sediments, and TEM in water showed significant correlations with DIAZ and NDZ in sediments. Environmental risk assessment revealed that NDZ and OXZ presented low ecological risks in both matrices at all sites, whereas DIAZ and TEM posed medium to high risks at certain water sites, with DIAZ also showing medium risks in some sediments. The study provides an integrated evaluation of occurrence, spatial distribution, and ecological risks of DIAZ and its metabolites in aquaculture systems, offering critical evidence to support food safety measures and strategies for pharmaceutical pollution control in the Pearl River Delta.