Florence Bonvin

Occurrence and fate of micropollutants in the Vidy Bay of Lake Geneva, Switzerland. Part II: Micropollutant removal between wastewater and raw drinking water.

The occurrence and removal of 58 pharmaceuticals, endocrine disruptors, corrosion inhibitors, biocides, and pesticides, were assessed in the wastewater treatment plant (WWTP) of the city of Lausanne, Switzerland, as well as in the effluent-receiving water body, the Vidy Bay of Lake Geneva. An analytical screening method to simultaneously measure all of the 58 micropollutants was developed based on ultra performance liquid chromatography coupled to a tandem mass spectrometer (UPLC-MS/MS). The selection of pharmaceuticals was primarily based on a prioritization study, which designated them as environmentally relevant for the Lake Geneva region. Except for the endocrine disruptor 17alpha-ethinylestradiol, all substances were detected in 24-h composite samples of wastewater entering the WWTP or in the treated effluent. Of these compounds, 40% were also detected in raw drinking water, pumped from the lake 3 km downstream of the WWTP. The contributions of dilution and degradation to micropollutant elimination between the WWTP outlet and the raw drinking water intake were established in different model scenarios using hypothetical residence times of the wastewater in Vidy Bay of 1, 4, or 90 d. Concentration decrease due to processes other than dilution was observed for diclofenac, beta-blockers, several antibiotics, corrosion inhibitors, and pesticides. Measured environmental concentrations (MECs) of pharmaceuticals were compared to the predicted environmental concentrations (PECs) determined in the prioritization study and agreed within one order of magnitude, but MECs were typically greater than the corresponding PECs. Predicted no-effect concentrations of the analgesic paracetamol, and the two antibiotics ciprofloxacin and sulfamethoxazole, were exceeded in raw drinking water samples and therefore present a potential risk to the ecosystem.

Direct Photolysis of Human Metabolites of the Antibiotic Sulfamethoxazole: Evidence for Abiotic Back-Transformation

The presence of potentially persistent and bioactive human metabolites in surface waters gives rise to concern; yet little is known to date about the environmental fate of these compounds. This work investigates the direct photolysis of human metabolites of the antibiotic sulfamethoxazole (SMX). In particular, we determined photolysis kinetics and products, as well as their concentrations in lake water. SMX, N-acetyl sulfamethoxazole, sulfamethoxazole β-D-glucuronide, 4-nitroso sulfamethoxazole, and 4-nitro sulfamethoxazole were irradiated under various light sources and pH conditions. All investigated metabolites, except sulfamethoxazole β-D-glucuronide were found to be more photostable than SMX under environmentally relevant conditions. Between two and nine confirmed photoproducts were identified for SMX-metabolites through ultraperformance liquid chromatography/high-resolution mass spectrometry. Interestingly, photolytic back-transformation to SMX was observed for 4-nitroso-SMX, indicating that this metabolite may serve as an environmental source of SMX. Moreover, two human metabolites along with SMX were regularly detected in Lake Geneva. The knowledge that some metabolites retain biological activity, combined with their presence in the environment and their potential to retransform to the parent compound, underlines the importance of including human metabolites when assessing the effects of pharmaceuticals in the environment.

Spatial and Temporal Presence of a Wastewater-Derived Micropollutant Plume in Lake Geneva

This study discusses the occurrence and environmental risk associated with a micropollutant plume originating from the direct discharge of treated wastewater into the Vidy Bay of Lake Geneva, Switzerland. The temporal variations and spatial extent of the plume and its effect on the presence of 39 pharmaceuticals and other micropollutants in the Vidy Bay were assessed over a 10 month period. A pronounced plume was observed from April to October, leading to locally elevated (up to 70-fold) pharmaceutical concentrations compared to the surrounding water column. For three of the measured substances, these plume-associated concentrations were sufficiently high to pose an ecotoxicological risk. The plume depth followed the thermal lake stratification, which moved to lower depths over the course of the warm seasons. Pharmaceutical hotspots associated with the plume were detected as far as 1.5 km downstream of the effluent wastewater outfall, but concentrations typically decreased with increasing distance from the wastewater outfall as a result of dilution and photodegradation. From November to January, when uniform temperature prevailed throughout the water column, no micropollutant plumes were detected. In contrast to pharmaceuticals, most pesticides showed homogeneous concentrations throughout the Vidy Bay during the whole study period, indicating that the effluent wastewater was not their dominant source. A strong linear correlation between electrical conductivity and concentrations of wastewater-derived micropollutants was identified. This relation will allow future estimates of wastewater-derived micropollutant concentrations via simple conductivity measurements.

Direct effects of dominant winds on residence and travel times in the wide and open lacustrine embayment: Vidy Bay (Lake Geneva, Switzerland)

Numerical simulations were carried out to determine the residence (or flushing) time of water in Vidy Bay (north shore of Lake Geneva) for different meteorological conditions. A hydrodynamic model (Delft3D-FLOW) was applied to simulate the flow field in the embayment during 2010 and January 2011. Using these results, particle tracking was applied to estimate transport of wastewater effluent discharged into the embayment. The model predictions compared well with published field measurements of dissolved species (as given by electrical conductivity profiles) within the wastewater. The pelagic boundary of the embayment was defined by the largest within-bay gyre. Based on this definition, particle tracking was used to quantify the residence time under dominant wind conditions. Similarly, particle tracking was used to determine the travel time (i.e., time to exit the embayment) for each of Vidy Bay’s three inflows (stream, stormwater and wastewater effluent). Although the wind field over the lake is variable, current patterns in the embayment can be simulated using the hydrodynamic model forced by a spatially uniform wind field. For a given wind speed, the main factor influencing residence and travel times is the wind angle. The presence of gyres leads to high mean residence times with large variability. As the wind direction becomes more aligned with the shoreline (i.e., with increasing westerly or easterly components), longshore currents dominate. These disrupt gyre formation and markedly reduce the mean and variability of embayment residence time. The numerical model was utilized to assess the potential for plume movement (in plan) from above the wastewater effluent outfall towards one of Lausanne’s drinking water intakes. In the most direct pathway, westward longshore currents can move water from the embayment to the water column above the intake location.

Micropollutant Dynamics in Vidy Bay—A Coupled Hydrodynamic-Photolysis Model to Assess the Spatial Extent of Ecotoxicological Risk

The direct discharge of effluent wastewater into Vidy Bay (Lake Geneva) results in the formation of an effluent plume with locally high concentrations of wastewater-derived micropollutants. The micropollutant hotspots above the wastewater outfall present a potential ecotoxicological risk, yet the spatial extent of the plume and the associated ecotoxicological risk zone remain unclear. This work combines the two main processes affecting the spreading of the plume, namely dilution of micropollutants due to mixing and degradation by photolysis, into a coupled hydrodynamic-photolysis model, with which we estimated the spatial extent of the risk zone in Vidy Bay. The concentration of micropollutants around the wastewater outfall was simulated for typical wind scenarios and seasons relevant to Vidy Bay, and the resulting ecotoxicological risk was evaluated. Specifically, we determined the direct and indirect photolysis rate constants for 24 wastewater-derived micropollutants and implemented these in a hydrodynamic particle tracking model, which tracked the movement of water parcels from the wastewater outfall. Simulations showed that owing to thermal stratification, the zone of ecotoxicological risk is largest in summer and extends horizontally over 300 m from the outfall. Photolysis processes contribute to reducing the plume extent mainly under unstratified conditions when the plume surfaces. Moreover, it was shown that only a few compounds, mainly antibiotics, dominate the total ecotoxicological risk.

Application of δ(18)O, δ(13)CDIC, and major ions to evaluate micropollutant sources in the Bay of Vidy, Lake Geneva.

Waters were sampled monthly from a profile at the wastewater outlet and a reference point in the Bay of Vidy (Lake Geneva) for a year. The samples were analyzed for 18O/16O of water, 13C/12C of dissolved inorganic carbon (DIC), major ions, and selected micropollutant concentrations. δ18O values, combined with the major ion concentrations, allowed discharged waste and storm-drainage water to be traced within the water column. On the basis of δ18O values, mole fractions of wastewater (up to 45 %), storm-drainage (up to 16 %), and interflowing Rhône River water (up to 34 %) could be determined. The results suggest that the stormwater fractions do not influence micropollutant concentrations in a measurable way. In contrast, the Rhône River interflow coincides with elevated concentrations of Rhône River-derived micropollutants in some profiles. δ13C values of DIC suggest that an increase in micropollutant concentrations at the sediment–water interface could be related to remineralization processes or resuspension.