Growth and physiological responses of spearmint (Mentha spicata) cuttings to norfloxacin

The increasing global consumption of antibiotics is a growing concern for the scientific community since the residues discharged into the environment can accumulate in plants and affect their growth. Mentha spicata L. is commonly used as a spice and widely cultivated as a medicinal and edible crop under controlled environments. Our study aimed to assess the subacute toxicity of norfloxacin (NOR; 0, 5, 10, 20, and 40 mg/L) on M. spicata cuttings and investigate the degradation of NOR in hydroponics during a 14-day exposure under natural conditions. In response to NOR, there were concentration-dependent declines in biomass, chlorophyll a, root activity, root elongation, and obvious chlorosis. An increase in malondialdehyde content and antioxidant activity indicated that NOR exposure specifically led to oxidative stress. There was a slight rise in osmotic regulatory substances observed in the setups treated with NOR compared to the control group. Simultaneously, M. spicata also made a response to the stress of NOR, and phytodegradation plays a more significant role in the degradation of NOR, in addition to hydrolysis and photodegradation processes. The integrated biomarker responses vesion 2 index values gradually increased with rising exposure concentrations, which suggested that NOR had toxic effects on M. spicata. These findings will improve the understanding of fluoroquinolones antibiotic effects on plants.