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  • 1
    Language: English
    In: Water, Air, & Soil Pollution, 2019, Vol.230(3), pp.1-14
    Description: Engineered nanoparticles (NP) like Ag and TiO 2 offer unique properties for various applications. Thus, the entry of the NP in soil environments is expected to increase in the future due to their growing industrial use. To avoid potential hazards due to these anthropogenic products, NP behavior in the environment should be well understood. In natural soil solutions, we investigated NOM adsorption onto Ag and TiO 2 NP and its influence on NP colloidal stability. Therefore, we extracted soil solutions from a floodplain soil (Fluvisol) and a farmland soil (Cambisol) differing in NOM quality and inorganic ion concentration. We measured the amount of adsorbed organic carbon as well as changes in aromaticity and molecular weight of NOM upon adsorption onto NP. Additionally, the size and zeta potential of NP in both soil solutions were investigated. We observed that the highly hydrophilic NOM of floodplain soil solution rich in inorganic ions strongly adsorbed to Ag but not to TiO 2 NP. Instead, sorption to TiO 2 NP was observed for the more hydrophobic NOM of the farmland soil with low ionic strength which did not sorb to Ag NP. These differences had a strong effect on NP stability, leading to Ag NP destabilization in case of floodplain soil solution and TiO 2 NP stabilization in the presence of farmland soil solution. Our results point out the necessity of studies in more complex systems and suppose that oxic and metallic NP might show very different fate depending on the environment they are exposed to.
    Keywords: Nanomaterial ; Soil extract ; Molecular weight ; Aromatic compounds ; Organic coating ; Ionic strength
    ISSN: 0049-6979
    E-ISSN: 1573-2932
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  • 2
    Language: English
    In: Science of the Total Environment, 15 December 2018, Vol.645, pp.192-204
    Description: Riverbank filtration systems are important structures that ensure the cleaning of infiltrating surface water for drinking water production. In our study, we investigated the potential risk for a breakthrough of environmentally aged silver nanoparticles (Ag NP) through these systems. Additionally, we identified factors leading to the remobilization of Ag NP accumulated in surficial sediment layers in order to gain insights into remobilization mechanisms. We conducted column experiments with Ag NP in an outdoor pilot plant consisting of water-saturated sediment columns mimicking a riverbank filtration system. The NP had previously been aged in river water, soil extract, and ultrapure water, respectively. We investigated the depth-dependent breakthrough and retention of NP. In subsequent batch experiments, we studied the processes responsible for a remobilization of Ag NP retained in the upper 10 cm of the sediments, induced by ionic strength reduction, natural organic matter (NOM), and mechanical forces. We determined the amount of remobilized Ag by ICP-MS and differentiated between particulate and ionic Ag after remobilization using GFAAS. The presence of Ag-containing heteroaggregates was investigated by combining filtration with single-particle ICP-MS. Single and erratic Ag breakthrough events were mainly found in 30 cm depth and Ag NP were accumulated in the upper 20 cm of the columns. Soil-aged Ag NP showed the lowest retention of only 54%. Remobilization was induced by the reduction of ionic strength and the presence of NOM in combination with mechanical forces. The presence of calcium in the aging- as well as the remobilizing media reduced the remobilization potential. Silver NP were mainly remobilized as heteroaggregates with natural colloids, while dissolution played a minor role. Our study indicates that the breakthrough potential of Ag NP in riverbank filtration systems is generally low, but the aging in soil increases their mobility. Remobilization processes are associated to co-mobilization with natural colloids.
    Keywords: Heteroaggregation ; Nanoparticle Transformation ; Breakthrough ; Mobility ; Reversibility ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 3
    Language: English
    In: Science of the Total Environment, 20 October 2019, Vol.688, pp.288-298
    Description: The colloidal stability of nanoparticles NP in soil solution is important to assess their potential effects on ecosystems. The aim of this work was to elucidate the interactions between initial particle size d , particle number concentration (N ) as well as the characteristics of dissolved organic matter (DOM) for stabilizing Ag NP and TiO NP. In batch experiments using time-resolved dynamic light scattering (DLS), we investigated the aggregation of TiO NP (79 nm, 164 nm) and citrate-stabilised Ag NP (73 nm, 180 nm) in Ca solution (2 mM) and two soil solutions, one extracted from a farmland and one from a floodplain soil (each containing 2 mM Ca ). Our results demonstrate that the initial particle size and the particle number concentration affected aggregation more strongly in the presence of DOM than without DOM. The composition of DOM also affected aggregate size: NP formed larger aggregates in the presence of hydrophilic DOM than in the presence of hydrophobic DOM. Hydrophilic DOM showed a larger charge density than hydrophobic DOM. If Ca is present, it may bridge DOM molecules, which may lead to greater NP destabilization. The results demonstrate that DOM interaction with NP may not only vary for different DOM characteristics (i.e. charge density) but may also be influenced by the presence of multivalent cations and different NP material; thus the effect of DOM on NP colloidal stability is not uniform.
    Keywords: Particle Size Effect ; Particle Number Concentration ; Hydrophilic DOM ; Batch Experiment ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    Language: English
    In: Environmental Science and Pollution Research, 2019, Vol.26(16), pp.15905-15919
    Description: Where 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 CeO 2 NP coated by the synthetic polymer polyacrylic acid (PAA) with CeO 2 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 Ca 2+ (soft) and 4.5 mM Ca 2+ (hard), respectively. Furthermore, the relevance of these findings was validated in a near-natural bank filtration experiment using HA-CeO 2 NP. PAA-CeO 2 NP were mobile under all tested water conditions, showing a breakthrough of 60% irrespective of the Ca 2+ concentration. In contrast, NOM-CeO 2 NP showed a lower mobility with a breakthrough of 27% in DI and 〈 10% in soft surface water. In hard surface water, NOM-CeO 2 NP were completely retained in the first 2 cm of the column. The transport of HA-CeO 2 NP in laboratory columns in soft surface water was lower compared to NOM-CeO 2 NP with a strong accumulation of CeO 2 NP in the first few centimeters of the column. Natural coatings were generally less stabilizing and more susceptible to increasing Ca 2+ concentrations than the synthetic coating. The outdoor column experiment confirmed the low mobility of HA-CeO 2 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, CeO 2 NP mobility may vary significantly depending on the surface coating.
    Keywords: Cerium dioxide mobility ; Nanomaterial transport ; Sediment column ; Riverbank filtration ; Colloidal stability ; Hydrochemical conditions ; Surface water
    ISSN: 0944-1344
    E-ISSN: 1614-7499
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