Fluoroquinolone and sulfonamide antibiotics (single and mixtures) impair the motor function of zebrafish larvae at environmentally relevant concentrations.

The occurrence of antibiotics in freshwater is a global concern, with evidence pointing to potential neurotoxic effects after prolonged exposure. However, data on their impact on behavior, particularly at environmentally relevant concentrations, remain limited. This study examined the motor function of zebrafish larvae exposed to single and mixture of antibiotics from the sulfonamide and fluoroquinolone classes. Ten antibiotics were assessed, namely, fluoroquinolones: ciprofloxacin (CIP), norfloxacin (NOR), pefloxacin (PEF), ofloxacin (OFL), and enrofloxacin (ENR) and sulfonamides: sulfamethoxazole (SMX), sulfadiazine (SDZ), sulfamethazine (SMZ), sulfamerazine (SMR), and sulfadimethoxine (SDM). After 24 h of exposure, single exposures revealed that all antibiotics disrupted at least one typical larval behavior at environmentally relevant concentrations. Larvae showed similarities in the escape response provoked by a vibrating acoustic stimulus (startle) according to the antibiotic class, despite the significantly more severe effects of SDM on startle and SMX on habituation to repetitive acoustic stimulation. Exposures to sulfonamide mixtures caused a non-monotonic effect on the startle response and significantly increased the distance traveled over the visual motor response. On the other hand, fluoroquinolone mixtures at 0.1 and 10 μg L reduced the habituation of zebrafish larvae. Biochemical markers suggest sulfonamide mixtures can potentially decrease catalase activity, whereas reduced glutathione levels are increased in fluoroquinolone mixtures at 10 μg L. Such findings support recent discussions on the potential of antibiotics to impair motor function in aquatic species, whether in isolated or combined forms. Regulatory mechanisms focused on discharging those substances into freshwater are pivotal to preventing adverse effects and ensuring biota safety.