Multilevel responses of Ceriodaphnia dubia, Nitellopsis obtusa and Lemna minor to selected veterinary antibiotics

Veterinary antibiotics are increasingly detected in surface waters, yet chronic and multigenerational ecotoxicological data remain limited for many aquatic taxa. This study examined the long-term effects of three widely used veterinary antibiotics – ciprofloxacin (CIP), sulfamethoxazole (SMX), and tetracycline (TC) – on freshwater species representing ecologically distinct functional groups and exposure pathways: the zooplankton Ceriodaphnia dubia, the benthic macroalga Nitellopsis obtusa, and the floating aquatic plant Lemna minor. TC induced the most consistent and severe responses, including survival reduction in all taxa and reproductive and somatic effects in C. dubia. CIP caused multigenerational reproductive inhibition in C. dubia from 0.1 mg/L, with survival reductions in later generations (F2–F3), and significantly inhibited duckweed growth (0.3–1.0 mg/L). SMX exhibited biphasic effects on reproduction, with stimulation at 0.1 mg/L and inhibition at 5 mg/L, while moderately affecting the survival of N. obtusa and the growth of L. minor. All three antibiotics induced oxidative stress in L. minor, as confirmed by elevated hydrogen peroxide and malondialdehyde levels, which occurred at concentrations lower than those that inhibited the growth of duckweed. Across all tested compounds, L. minor responded at lower concentrations than N. obtusa, underscoring its sensitivity and value as a phytotoxicity indicator. Importantly, C. dubia exhibited increasing susceptibility in later generations, highlighting the reliability of multigenerational testing. These findings emphasise the compound-specific and time-dependent nature of antibiotic toxicity and the ecological importance of integrating macrophytes, benthic algae, and reproductive endpoints into regulatory ecotoxicological frameworks for pharmaceuticals.