Bioconcentration, biotransformation, oxidative stress and neurochemical response of environmental concentration diazepam in yellowbelly pufferfish.

The benzodiazepine diazepam is an emerging environmental contaminant that poses a potential threat to ecosystems and human health. However, there are knowledge gaps regarding tissue-specific accumulation and biotransformation, and the potential toxicity of diazepam in economically important fish at environmental concentrations. This study explored the tissue distribution and accumulation of diazepam and its metabolites in juvenile yellowbelly pufferfish after 35 days of exposure to environmentally relevant concentrations (2, 20, and 100 ng/L). Additionally, changes in oxidative stress markers and neurotransmitter levels were analyzed during a 35-day exposure period and a 7-day recovery period. Our results showed that after 35-day exposure, diazepam exhibited the highest accumulation in the liver tissue of yellowbelly pufferfish, followed by the brain tissue. Moreover, biotransformation occurred in vivo, including demethylation and hydroxylation. Significant differences in superoxide dismutase, catalase, and glutathione peroxidase enzyme activity between the medium and high-level treatment groups reflected the compensatory effect of antioxidant defenses, while the unchanged malondialdehyde levels indicated their strong antioxidant stress capacity. Furthermore, the down-regulation of key neurotransmitters (glutamate, γ-aminobutyric acid, dopamine, 5-hydroxytryptamine, and norepinephrine) in brain tissues during the exposure period and recovery period confirms the high potential for neurotoxicity at environmental concentrations of diazepam. These results provide fundamental support for an in-depth understanding of the tissue-specific accumulation and potential toxicity of diazepam and its metabolites to marine organisms.