Identification of fluoroquinolone antibiotics as the main source of umuC genotoxicity in native hospital wastewater

Previous work revealed genotoxic effects in the wastewater of a large university hospital using a bacterial short-term genotoxicity assay, based on a umuC::lacZ fusion gene (umuC assay). These studies ruled out disinfectants and detergents as main causative agents of the genotoxic effects. This paper focuses on specific hospital-related drugs as the cause. The ratio of theoretical mean wastewater concentrations (derived from consumption data) and lowest observable effect concentrations of selected pharmaceuticals were used to calculate umuC induction probabilities. The fluoroquinolone antibiotics Ciproxin(R) and Noroxin(R) showed the highest induction probabilities and exceeded all other investigated drugs by at least one order of magnitude in significance. Antineoplastic drugs, originally thought to be the main effecters, were found to be of marginal significance using the umuC assay. These findings were further supported by investigation of urine samples of hospital patients with the umuC assay. The determination of ciprofloxacin in native hospital wastewater by reversed-phase high-performance liquid chromatography and fluorescence detection revealed concentrations from 3 to 87 mu g/L. umuC induction factor and ciprofloxacin concentrations in 16 hospital wastewater samples showed a log-linear correlation (r(2) = 0.84, p < 0.0001). These results suggest that the previously measured umuC genotoxicity in the wastewater of the hospital under investigation is caused mainly by fluoroquinolone antibiotics, especially by ciprofloxacin. On the basis of these findings, the role of the umuC assay as a screening tool for wastewater genotoxicity assessment is discussed.