Ecotoxicological effects of nadifloxacin on the swimming behaviour of Daphnia magna

Background: Nadifloxacin (NDFX) is a chiral fluoroquinolone widely used as a topical treatment for inflammatory acne lesions [1] and is frequently detected in aquatic environments due to its persistence and inefficient removal in wastewater treatment plants [2, 3]. Its environmental presence raises concerns about potential enantioselective effects on non-target aquatic organisms. However, toxicity data for freshwater invertebrates such as Daphnia magna remain scarce, highlighting the need to evaluate its potential ecological risks. Objective: This study aimed to assess the potential sub-chronic effects of NDFX racemate and its individual enantiomers on Daphnia magna by evaluating swimming behaviour endpoints. Methods: Sub-chronic exposure assays initiated using neonates (<24 h) exposed for 9 days to 100 µg.L⁻¹ of racemic NDFX or each isolated enantiomer. Each treatment consisted of 5 replicates, with 20 organisms per replicate. After the exposure period, swimming behaviour endpoints (swimming speed, swimming activity, and total distance travelled) were assessed through the analysis of 1-min video recordings. Results: No significant changes in swimming behaviour endpoints were observed in organisms exposed to either NDFX racemate or its isolated enantiomers. Conclusions: Overall, NDFX exposure did not cause significant changes in swimming behaviour in Daphnia magna, and no enantioselective effects were observed under the tested conditions. Further studies are required to clarify the potential mechanisms of NDFX toxicity in aquatic organisms.