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Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (VIII, 116 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018, Silver nanoparticles (AgNP) find a wide application due to their physical-chemical properties and antimicrobial activity. Through the rising consumption of products containing AgNP, the release of AgNP in the environment is becoming ever more likely and, as such, AgNP can end up in soil. Information on the behavior and fate of AgNP in soil is essential for risk assessment. Therefore, the aim of this study is to investigate the transport and retention behavior of surface modified AgNP such as surfactant-stabilized AgNP and polyvinylpyrrolidone-stabilized AgNP (PVP-AgNP) in soil at environmentally relevant conditions. The investigations of this thesis include the influence of environmentally relevant weather conditions such as dry periods and rain events with different rain intensities, as well as tillage on the transport and retention of surfactant-stabilized AgNP in an arable loamy sand soil. Furthermore, the distribution, identification and characterization of aged surfactant-stabilized AgNP–soil associations, as well as the impact of chemical surface heterogeneity on the transport and retention of PVP-AgNP was studied. AgNP concentrations for breakthrough curves (BTCs) and retention profiles (RPs) were analyzed by inductively coupled plasma mass spectrometry (ICP-MS).The effect of wet and dry weather events on the transport and retention on surfactant-stabilized AgNP was simulated by conducting water-unsaturated undisturbed soil column experiments with flow interruption (FI) and variable ionic strength (IS). The results were compared to those obtained under continuous flow conditions. Experimental results were simulated using a numerical model that considers reversible attachment of AgNP at the soil–water interface and irreversible attachment at the air–water interface (AWI). BTCs of AgNP showed a dramatic drop after FI compared to continuous flow conditions. Evaporation increased due to FI, resulting in increased electrical conductivity (EC) of the soil solution, which led to a totally reduced mobility of AgNP. A reduction of IS after FI enhanced AgNP mobility slightly. Here the strongly increased aluminum (Al) and iron (Fe) concentration in the effluent suggested that soil colloids facilitated the release of AgNP (cotransport). The numerical model reproduced the measured AgNP BTCs and indicated that attachment to AWI occurring during FI was the key process for AgNP retention. Undisturbed outdoor lysimeters were used to examine the influence of either heavy rain events (short rain events of high frequency and high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the long-term transport and retention behavior of surfactant-stabilized AgNP in soil. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the ploughed A (Ap) horizon. High rain intensities cause higher infiltration rates, pore water velocity and soil colloid mobilization and thus could contribute to the mobilization of AgNP and AgNP–soil colloid associations. The AgNP–soil associations within the Ap horizon were analyzed by means of soil particle- size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis- detection and ICP-MS (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil particles. In particular, water-dispersible colloids (WDC) of the soil in the size range of 0.45–0.1 µm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids composed of Al, Fe, and silicon. These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homoaggregated, and small AgNP probably due to dissolution.The impact of chemical surface heterogeneity on the transport and retention of PVP-AgNP was studied in water-saturated goethite coated quartz sand (GQS) columns with various mass percentages of GQS in the mixed porous medium. The BTCs indicated that PVP-AgNP mobility decreased with increasing GQS proportion. By increasing the mass percentage of GQS in the mixed porous media, the attachment conditions for negative surface charged AgNP became more favorable due to the increase of the positively charged surface area and surface roughness of the collector, and thus led to increased AgNP retention. Transport experiments in water-unsaturated undisturbed soil columns were performed with simulated soil tillage after the application of surfactant-stabilized AgNP and compared to those conducted without soil tillage. Soil tillage and direct irrigation reduced the mobility slightly due to the temporarily destroyed pore structure and flow paths, which was related to lower flow velocity, and increased EC of the soil solution. Overall, the results provide important insights into the environmental fate of AgNP and indicated AgNP retention in soil at above mentioned conditions., Published by Aachen