Mechanisms underlying the chronic toxicity of ofloxacin to Daphnia magna: Oxidative stress, mitochondrial dysfunction, and energy allocation

Ofloxacin (OFL), a fluoroquinolone antibiotic, has attracted attention due to its extensive use and frequent environmental detection, posing ecological risks in aquatic systems. Herein, a multilevel ecotoxicity assessment of OFL (0.01, 0.1, 1, and 10 mg/L) was conducted on an ecotoxicology model, Daphnia magna, using a 21-day chronic test. The involved parameters included mitochondrial function, metabolites, digestive enzymes, oxidative stress, development, reproduction, locomotor behavior, and multi-omic analysis. Environmentally relevant concentration of OFL (0.01 mg/L) exposure elicited detrimental effects on redox homeostasis, intestinal flora, and lipid metabolism in D. magna. It is noteworthy that hormetic effects were observed in reproductive capacity in D. magna exposed to OFL. Furthermore, exposure to elevated contamination concentrations of OFL (0.1, 1, and 10 mg/L) led to pronounced oxidative stress in D. magna, resulting in gut damage and reduced digestive enzymes and metabolites. Notably, exposure to 10 mg/L OFL induced marked mitochondrial dysfunction and shortage of lipid metabolites in the D. magna, leading to the destruction of energy supply and impairment of locomotor, development, and reproduction. This study comprehensively assessed the aquatic ecological risks of OFL and provided insights into the mechanisms underlying the toxicity of OFL on the development, reproduction, and energy allocation of D. magna.