Transport and fate of manufactured silver nanoparticles in saturated heterogeneous natural porous media
P 13.3 in Reactive transport modeling
Nowadays a variety of nanoparticles is used in many products in daily life. Silver nanoparticles play an important role due to their antimicrobial properties. They are widely used in textiles and personal care products. Additionally, it has been shown that silver nanoparticles are to a large part removed from wastewater in waste water treatment plants and retained in sewage sludge, which is then used as fertilizer in agriculture (Maier, 2012). As such, the likelihood that nanoparticles enter soil and groundwater is increased. Several recent (Braun et al., 2015; El Badawy et al., 2013) studies have focused on the transport of silver nanoparticles with different surface coatings. These studies used idealized column tests to investigate the behavior of silver nanoparticles on spherically shaped glass beads or quartz grains with and without surface coatings or examined the transport behavior of silver nanoparticles in saturated natural soils. However, although groundwater and spring water are the major sources of drinking-water in Germany, studies investigating the transport of silver nanoparticles in aquifer materials under realistic hydrochemical conditions are lacking.
To close this gap, we conducted several column experiments to study the breakthrough of silver nanoparticles in aquifer material. Each column was spiked with three pore volumes of a silver solution containing 60 mg Ag L− 1 surfactant stabilized silver nanoparticles before eluted at different flow rates. As background ions different solutions consisting of NaNO3, Ca(NO3)2 at different ionic strength and artificial groundwater were chosen. The aquifer material was collected from a drilling of a monitoring well near Dormagen, NRW, Germany and consisted of heterogeneous particles with different shapes and grains with and without iron oxide and hydroxide coatings. It was dominated by quartz and albite, and contained about 1% of hematite as determined by X-ray diffractometry. Breakthrough of the silver nanoparticles was measured by ICP-MS and the nanoparticle size was determined using dynamic light scattering (DLS). Breakthrough curves were modeled using the numerical transport model HYDRUS-1D. Initial results show a high breakthrough at low ionic strength for monovalent ions compared to divalent ions with the same ionic strength or artificial groundwater. No breakthrough was observed for high ionic strength for monovalent and divalent cations at different flow rates. Our initial findings show that silver nanoparticles can be retained due to chemical and physical heterogeneities to a low extend.
Braun, A.; E., K.; Azzam, R. & Neukum, C. (2015): Transport and deposition of stabilized engineered silver nanoparticles in water saturated loamy sand and silty loam, Science of the Total Environment, 535, 102-112.
Maier, M.; Letzel, M.; Wegenke, M. (2012): Verhalten von Nanopartikeln in Kläranlagen, Mitteilungen der Fachgruppe Umweltchemie und Ökotoxikologie, 18, 62-65.
El Badawy, A. M.; Hassan, A. A.; Scheckel, K. G.; Suidan, M. T.; Tolaymat, T. M. (2013): Key Factors Controlling the Transport of Silver Nanoparticles in Porous Media, Environmental Science & Technology, 47, 4037-4045.