Silver Nanoparticle Levels in River Water: Real Environmental Measurements and Modeling ApproachesA Comparative Study

Due to severe analytical challenges, methods for quantification of silver-based nanoparticles (Ag-b-NPs) in environmental samples are scarce. Modeling approaches try to overcome these limitations, paving a way for valid concentration data of nanomaterials in the environment essential for comprehensive risk assessments. However, a comparison of both analytical and modeling approaches is essential to ensure validity and reliability of measurements and estimates. Here, we present analytical measurements of Ag-b-NPs in the River Isar in southern Germany, sampled from its source to the confluence with the river Danube. A stable level of approximately 1–2 ng L–1 of Ag-b-NPs was measured in the river, whereas concentration peaks near wastewater treatment plants (WWTPs) climbed to 2.47–69.08 ng L–1 of Ag-b-NPs but were quickly diluted to the stable level in the river’s reach. Simultaneously, a one-dimensional model approach successfully reproduced measured Ag-b-NP concentrations and distribution. Predictions rested upon data about population size, flow velocities, and WWTP removal efficiencies. It was assumed that WWTPs can be modeled as point sources and that the wastewater is mixed quickly over the river’s cross section. The model distinguished between unabsorbed and adsorbed Ag-b-NPs and total silver and revealed that the NPs adsorb quickly to the suspended sediment in the river