Person: Pabst, Silke
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Veröffentlichung Transport and retention of differently coated CeO2 nanoparticles in saturated sediment columns under laboratory and near-natural conditions(2019) Degenkolb, Laura; Dippon-Deissler, Urs; Klitzke, Sondra; Pabst, SilkeWhere surface-functionalized engineered nanoparticles (NP) occur in drinking water catchments, understanding their transport within and between environmental compartments such as surface water and groundwater is crucial for risk assessment of drinking water resources. The transport of NP is mainly controlled by (i) their surface properties, (ii) water chemistry, and (iii) surface properties of the stationary phase. Therefore, functionalization of NP surfaces by organic coatings may change their fate in the environment. In laboratory columns, we compared the mobility of CeO2 NP coated by the synthetic polymer polyacrylic acid (PAA) with CeO2 NP coated by natural organic matter (NOM) and humic acid (HA), respectively. The effect of ionic strength on transport in sand columns was investigated using deionized (DI) water and natural surface water with 2.2 mM Ca2+ (soft) and 4.5 mM Ca2+ (hard), respectively. Furthermore, the relevance of these findings was validated in a near-natural bank filtration experiment using HA-CeO2 NP. PAA-CeO2 NP were mobile under all tested water conditions, showing a breakthrough of 60% irrespective of the Ca2+ concentration. In contrast, NOM-CeO2 NP showed a lower mobility with a breakthrough of 27% in DI and < 10% in soft surface water. In hard surface water, NOM-CeO2 NP were completely retained in the first 2 cm of the column. The transport of HA-CeO2 NP in laboratory columns in soft surface water was lower compared to NOM-CeO2 NP with a strong accumulation of CeO2 NP in the first few centimeters of the column. Natural coatings were generally less stabilizing and more susceptible to increasing Ca2+ concentrations than the synthetic coating. The outdoor column experiment confirmed the low mobility of HA-CeO2 NP under more complex environmental conditions. From our experiments, we conclude that the synthetic polymer is more efficient in facilitating NP transport than natural coatings and hence, CeO2 NP mobility may vary significantly depending on the surface coating. © The Author(s) 2019Veröffentlichung Colloidal stabilization of CeO2 nanomaterials with polyacrylic acid, polyvinyl alcohol or natural organic matter(2018) Dippon-Deissler, Urs; Pabst, Silke; Klitzke, SondraEngineered nanomaterials (ENM) such as nano-sized cerium dioxide (CeO2) are increasingly applied. Meanwhile, concerns on their environmental fate are rising. Understanding the fate of ENM within and between environmental compartments such as surface water and groundwater is crucial for the protection of drinking water resources. Therefore, the colloidal stability of CeO2 ENM (2 mg L-1) was assessed with various surface coatings featuring different physico-chemical properties such as weakly anionic polyvinyl alcohol (PVA), strongly anionic polyacrylic acid (PAA) or complex natural organic matter (NOM) at various water compositions in batch experiments (pH 2 - 12, ionic strength 0-5 mM KCl or CaCl2). While uncoated CeO2 ENM aggregate in the range of pH 4-8 in 1 mM KCl solution, the results show that PAA, PVA and NOM surface coatings stabilize CeO2-ENM at neutral and alkaline pH in 1 mM KCl solution. Stabilization by PAA and NOM is associated with strongly negative zeta potentials below -20 mV, suggesting electrostatic repulsion as stabilization mechanism. No aggregation was detected up to 5 mM KCl for PAA- and NOM-coated CeO2 ENM. In contrast, CaCl2 induced aggregation at >2.2 mM CaCl2 for PAA and NOM-coated CeO2 ENM respectively. PVA-coated ENM showed zeta potentials of -15 mV to -5 mV in the presence of 0-5 mM ionic strength, suggesting steric effects as stabilization mechanism. The hydrodynamic diameter of PVA-coated ENM was larger compared to PAA and NOM at low ionic strength, but the size did not increase with ionic strength of the suspensions. The effect of ionic strength and counter ion valency (pH 7) on the colloidal stability of ENM depends on the prevailing stabilization mechanism of the organic coating. NOM can be similarly effective in colloidal stabilization of CeO2-ENM as PAA. Our results suggest natural Ca-rich waters will lead to ENM agglomeration even of coated CeO2-ENM. © 2018 The Authors. Published by Elsevier B.V.