Environmental dynamic evaluation of fluoroquinolones in water-sediment microcosms and the effect in total coliforms...

The contamination of aquatic environments by anthropogenic activities leads to the release of emerging contaminants, including residual antibiotics, whose fate and transformation pathways remain poorly understood. This study evaluated the environmental dynamics of fluoroquinolone antibiotics in water-sediment microcosms and assessed how exposure influenced the abundance of total coliforms and Escherichia coli populations. Anaerobic microcosms were prepared using water and sediment collected from a preserved station in the Billings Reservoir (Brazil) and spiked with ciprofloxacin (CIPRO) at 10, 100, and 1000 μg L^-1 to assess attenuation and transformation processes. Sampling was conducted over 90 days, and CIPRO and its transformation products were quantified using high-performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Total coliforms and Escherichia coli were assessed using standardized bacteriological test kits. CIPRO half-lives were 33 days in dark microcosms and 11 days under light exposure, confirming photodegradation as a major transformation pathway. CIPRO was progressively adsorbed to the sediment until equilibrium, with distribution coefficients (Kd) of 2.00 and 1.40 L kg^-1 in dark and light systems, respectively. Multivariate analysis indicated positive correlations between CIPRO and pH, chemical oxygen demand, and dissolved organic carbon in the water, and a positive correlation with pH in the sediment. No clinical resistance endpoint was evaluated; instead, exposure to CIPRO led to a gradual decline in total coliform abundance, approaching near-undetectable levels on days 10 and 15. Norfloxacin was detected as a transformation product, retaining the quinolone core ring, while cleavage occurred at the cyclopropyl group terminus. In both dark and light conditions, CIPRO was not fully degraded. These findings highlight the persistence of fluoroquinolones in tropical reservoirs and their potential to alter microbial dynamics.