Abstract
Riverbank filtration (RBF) is used worldwide to produce high quality drinking water. With river water often contaminated by micropollutants (MPs) from various sources, this study addresses the occurrence and fate of such MPs at three different RBF sites with oxic alluvial sediments and short travel times to the drinking water well down to hours. A broad range of MPs with various physico-chemical properties were analysed with detection limits in the low ng L−1 range using solid phase extraction followed by liquid chromatography coupled to tandem high resolution mass spectrometry. Out of the 526 MPs targeted, a total of 123 different MPs were detected above the limit of quantification at the three different RBF sites. Of the 75–96 MPs detected in each river, 43–59% were attenuated during RBF. The remaining total concentrations of the MPs in the raw drinking water accounted to 0.6–1.6 μgL−1 with only a few compounds exceeding 0.1 μgL−1, an often used threshold value. The attenuation was most pronounced in the first meters of infiltration with a full elimination of 17 compounds at all three sites. However, a mixing with groundwater related to regional groundwater flow complicated the characterisation of natural attenuation potentials along the transects. Additional non-target screening at one site revealed similar trends for further non-target components. Overall, a risk assessment of the target and estimated non-target compound concentrations finally indicated during the sampling period no health risk of the drinking water according to current guidelines. Our results demonstrate that monitoring of contamination sources within a catchment and the affected water quality remains important in such vulnerable systems with partially short residence times.
Highlights
Riverbank filtration (RBF) is used worldwide as a natural process to produce high quality drinking water with relatively low environmental impact and at low capital costs (Maeng et al, 2011)
With river water often contaminated by micropollutants (MPs) from various sources, this study addresses the occurrence and fate of such MPs at three different RBF sites with oxic alluvial sediments and short travel times to the drinking water well down to hours
526 target compounds were selected based on consumption data and occurrence in former monitoring campaigns of surface and groundwater in Switzerland (Huntscha et al, 2012; Moschet et al, 2014; Schymanski et al, 2014) and covered pharmaceuticals (215), plant protection products, biocides (18), illicit drugs (11), perfluorinated compounds (PFCs, 16), others (23 including 8 food additives and 15 industrial compounds), as well as 101 major metabolites for which reference standards were available (Table S7, Fig. S1)
Summary
Riverbank filtration (RBF) is used worldwide as a natural process to produce high quality drinking water with relatively low environmental impact and at low capital costs (Maeng et al, 2011). Photolysis, sorption, dispersion, and volatilization influence the fate and attenuation of MPs in aquatic systems (Escher and Fenner, 2011; Gurr and Reinhard, 2006; Schwarzenbach et al, 2006) All these processes are affected by the physico-chemical properties of the compounds as well as the physical and biological parameters of the river, such as river flow rate, turbidity, dissolved oxygen concentration, pH, temperature, the structure of microbial communities, the hydraulic regime and the extent of hyporheic exchange in the river (Boulton et al, 2010). Several studies strongly indicate that natural attenuation is most pronounced already in the first few meters of infiltration, i.e., within the highly reactive hyporheic zone (Brunke and Gonser, 1997; Heberer et al, 2008; Huntscha et al, 2013; Lawrence et al, 2013; Regnery et al, 2015)
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