Enrofloxacin's dual effects on earthworms: Reproductive toxicity at environmental levels and growth promotion at elevated concentrations.

The extensive use of veterinary antibiotics like enrofloxacin (EF) has led to environmental accumulation, yet its ecological risks to soil fauna remain understudied. Earthworms, essential for soil health, were exposed to environmentally relevant (10 mg/kg) and growth-promoting (100 mg/kg) EF concentrations for 21 days to assess sublethal effects. At 10 mg/kg, EF had no significant impact on earthworm survival or growth but reduced cocoon production and downregulated the reproduction-related gene Annetocin precursor (ANN). DNA damage and increased expression of defense-related genes (CytochromeP450, CYP450; Heat Shock Protein 70, Hsp70) were also observed. In contrast, 100 mg/kg EF significantly promoted growth and upregulated ANN expression. It also activated antioxidant defenses, reducing reactive oxygen species (ROS) accumulation, and increased the expression of the defense gene Translationally controlled tumor protein (TCTP). Integrated biomarker response (IBR) analysis revealed that EF's effects at environmental concentrations diminished over time, while its impacts at higher concentrations persisted or intensified. These results highlight EF's complex, concentration-dependent effects, demonstrating that even sublethal exposures can alter key physiological and molecular functions in earthworms. The findings underscore the need for stricter regulation and long-term risk assessment of veterinary antibiotics in soil environments to safeguard soil biodiversity and functionality.