Spatio-Temporal Presence of Micropollutants and their Metabolites in Lake Geneva and Susceptibility to Direct and Indirect Photodegradation Processes

Invisible to the human eye, yet ubiquitous... The occurrence and the potential adverse effects of micropollutants in the environment are uncontested. Due to incomplete removal by conventional wastewater treatment technologies, the aquatic environment is contaminated with pharmaceuticals and other micropollutants (biocides, pesticides). This thesis discusses the occurrence and photolytic fate of micropollutants in the Vidy Bay of Lake Geneva, Switzerland and the resulting environmental risk. The spatio-temporal variations in the concentrations of 39 micropollutants were investigated during a 10-month sampling campaign, at different locations around a wastewater outfall in Vidy Bay. A pronounced wastewater plume was observed from April to October, leading to locally elevated pharmaceutical concentrations compared to the surrounding water column. 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 wastewater outfall, but concentrations typically decreased with increasing distance from the 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 in the vicinity of the plume. On the other hand, from November to January, when uniform temperature prevailed throughout the water column, the plume surfaced or was not detected due to enhanced mixing of the water column. 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. To overcome the limitations of punctual sampling, a more complete picture of the distribution of wastewater-derived micropollutants in Vidy Bay was obtained by augmenting field measurements with a validated model, which incorporates the most important physical and chemical attenuation processes. Given the importance of photolysis in the fate of many organic pollutants, we proposed a model which combines the current hydrodynamics via 3D particle tracking, and the depth-dependent photodegradation of micropollutants. Moreover, the total ecotoxicological risk associated with the predicted concentrations of all micropollutants concentrations was determined. Direct discharge of effluent wastewater into the Bay resulted in a limited zone, in which micropollutant concentrations were sufficiently high that commonly applied water quality criteria were exceeded. The resulting ecotoxicoloigcal risk could mainly be attributed to only three among the 24 wastewater-derived compounds investigated, namely three antibiotics. As expected, photodegradation was an important removal mechanism for many compounds and thus, along with