Environmental exposure and risk assessment of fluoroquinolone antibacterial agents in wastewater and river water of the Glatt Valley Watershed, Switzerland.

The mass flows of fluoroquinolone antibacterial agents (FQs) were investigated in the aqueous compartments of the Glatt Valley Watershed, a densely populated region in Switzerland. The major human-use FQs consumed in Switzerland, ciprofloxacin (CIP) and norfloxacin (NOR), were determined in municipal wastewater effluents and in the receiving surface water, the Glatt River. Individual concentrations in raw sewage and in final wastewater effluents ranged from 255 to 568 ng/L and from 36 to 106 ng/L, respectively. In the Glatt River, the FQs were present at concentrations below 19 ng/L. The removal of FQs from the water stream during wastewater treatment was between 79 and 87%. During the studied summer period, FQs in the dissolved fraction were significantly reduced downstream in the Glatt River (15-20 h residence time) (66% for CIP and 48% for NOR). Thus, after wastewater treatment, transport in rivers causes an additional decrease of residual levels of FQs in the aquatic environment. Refined predicted environmental concentrations for the study area compare favorably with the measured environmental concentrations (MEC) obtained in the monitoring study. Total measured FQ concentrations occurring in the examined aquatic compartments of the Glatt Valley Watershed were related to acute ecotoxicity data from the literature. The risk quotients obtained (MEC/PNEC < 1) following the recommendations of the European guidelines or draft documents suggest a low probability for adverse effects of the occurring FQs, either on microbial activity in WWTPs or on algae, daphnia, and fish in surface waters.