Degradation of a fluoroquinolone antibiotic in an urbanized stretch of the River Tiber

CIP residual concentrations were measured over time by using HPLC coupled to fluorescence detection (FLD) and the effects of the antibiotic on the natural microbial community were assessed in terms of live cell abundance. The key role of light in CIP disappearance was confirmed, but also its biodegradation in natural river water was demonstrated. In fact, differently from other experiments we found a higher degradation rate (DT50 = 10.4 d), in presence of both light and the natural river bacterial populations than in the same sterilized river water (DT50 = 18.4 d). Moreover, even in the dark, a partial CIP biodegradation was also observed (DT50 = 177 d). The overall results were supported by the increase in live cell numbers with the decrease of CIP concentrations both in the dark and light condition.