Bromazepam exposure alters early development, behavior, and induces oxidative stress in zebrafish

Abstract Bromazepam (BMZ) is a pharmaceutical drug of the benzodiazepine (BZD) class, commonly prescribed for its sedative, hypnotic, anxiolytic, and muscle relaxant properties. This medication has a higher abuse potential than other BZDs due to its rapid onset of action, moderate liposolubility, and pronounced anxiolytic effect mediated by the positive modulation of GABA A receptors. BMZ can be found in different aquatic matrices, mainly associated with sewage, industrial effluents, and surface waters, causing adverse effects on non-target species. Therefore, assessing whether BMZ causes biological effects at environmentally relevant concentrations in zebrafish, an important experimental model for the ecotoxicological assessment of pharmaceuticals, is crucial. Here, we assessed the effects of BMZ exposure during early development (3–120 hpf) at concentrations of 0, 7, 15 (a concentration detected in effluent samples), and 30 μg L −1 on survival, hatching, spontaneous movement, heart rate, locomotor activity, anxiety-like behavior, anti-predatory response, and antioxidant enzyme activity (catalase and superoxide dismutase). Exposure to BMZ decreased spontaneous movement ( p = 0.0123), increased heart rate ( p < 0.0001), altered locomotor behavior, and reduced the activity of antioxidant enzymes (catalase, p = 0.0408; superoxide dismutase, p = 0.0109) compared to the control group in zebrafish larvae. In this study, we demonstrate that BMZ exposure impairs the early development of zebrafish, affecting physiological, behavioral, and biochemical parameters that may reduce individual fitness and compromise survival, growth, and predator escape, highlighting the ecological risks posed by BMZ residues in contaminated aquatic environments.