Low-Dose Ciprofloxacin Exposure Modulates Growth, Total Phenolic Content, and Residue Accumulation in Lactuca sativa L. Grown Hydroponically

Pharmaceutical contamination of irrigation water is an increasing concern for food safety, especially in hydroponic systems where dissolved contaminants remain highly bioavailable. This study evaluated low-dose ciprofloxacin (CIP; 0, 1, 5, and 10 µg L−1) effects on fresh shoot biomass, total phenolic content, in vitro antioxidant capacity (ORAC and DPPH), and CIP residues in edible tissue of hydroponically grown lettuce (Lactuca sativa L.). Shoot biomass increased by 13%, 20%, and 30% with increasing CIP, without visible phytotoxicity, while total phenolic content and ORAC increased by up to 97% and 12.4%, respectively, and DPPH IC50 decreased by 38–44%. In contrast, apparent CIP residues in shoot tissue tended to be lower at 5 and 10 µg L−1 than at 1 µg L−1; given these values were below the method limit of quantification (LOQ), this pattern is reported only as an indicative trend, and possible explanations such as uptake saturation and/or detoxification remain hypotheses that were not tested here. These results suggest that low-dose CIP exposure can be associated with higher biomass and phenolic/antioxidant indicators without evidence of a proportional rise in quantifiable residues, offering preliminary insight for food safety assessment in antibiotic-contaminated hydroponic systems. As this remains a preliminary assessment based mainly on biomass, total phenolics, in vitro antioxidant capacity, and CIP residues, further physiological and molecular analyses are needed to confirm the underlying mechanisms, together with longer-term validation under real production conditions.