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  • 1
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.102(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.12.023 Byline: Anika Braun, Erwin Klumpp, Rafig Azzam, Christoph Neukum Abstract: It is considered inevitable that the increasing production and application of engineered nanoparticles will lead to their release into the environment. However, the behavior of these materials under environmentally relevant conditions is still only poorly understood. In this study the transport and deposition behavior of engineered surfactant stabilized silver nanoparticles (AgNPs) in water saturated porous media was investigated in transport experiments with glass beads as reference porous medium and in two natural soils under various hydrodynamic and hydrochemical conditions. The transport and retention processes of AgNPs in the porous media were elucidated by inverse modeling and possible particle size changes occurring during the transport through the soil matrix were analyzed with flow field-flow fractionation (FlFFF). A high mobility of AgNPs was observed in loamy sand under low ionic strength (IS) conditions and at high flow rates. The transport was inhibited at low flow rates, at higher IS, in the presence of divalent cations and in a more complex, fine-grained silty loam. The slight decrease of the mean particle size of the AgNPs in almost all experiments indicates size selective filtration processes and enables the exclusion of homoaggregation processes. Article History: Received 14 July 2014; Revised 21 November 2014; Accepted 7 December 2014
    Keywords: Nanoparticles – Analysis ; Silt – Analysis ; Loams – Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Water Research, 01 May 2013, Vol.47(7), pp.2572-2582
    Description: Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solution ionic strength (IS), and an increase in water velocity, sand grain size, and input concentration ( ). In contrast to conventional filtration theory, retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The experimental BTCs and RPs with uniform or hyperexponential shape were well described using a numerical model that considers time- and depth-dependent retention. The simulated maximum retained concentration on the solid phase ( ) and the retention rate coefficient ( ) increased with IS and as the grain size and/or decreased. The RPs were more hyperexponential in finer textured sand and at lower because of their higher values of . Conversely, RPs were nonmonotonic or uniform at higher and in coarser sand that had lower values of , and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when was approaching filled conditions. Nonmonotonic RPs had peak concentrations at greater distances in the presence of excess amounts of surfactant, suggesting that competition between AgNPs and surfactant diminished close to the column inlet. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum. However, elimination of the secondary minimum only produced recovery of a small portion (〈10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity. ► The presence of surfactant affected the shape of the retention profiles (RPs). ► RPs transitioned from hyperexponential, to nonmonotonic, and then to uniform. ► Nanoparticles mainly irreversibly interacted with microscopic heterogeneity.
    Keywords: Stabilized Silver Nanoparticles ; Saturated Porous Media ; Time- and Depth-Dependent Retention ; Surfactant ; Competitive Attachment ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 3
    Language: English
    In: Chemosphere, November 2012, Vol.89(11), pp.1376-1383
    Description: ► Oxidative and reductive degradation of xenobiotics is simulated successfully. ► Model substances for NOM are suggested and evaluated. ► Possible reactions of the model substances and the xenobiotics and/or their degradation products are elucidated. Risk assessment of xenobiotics requires a comprehensive understanding of their transformation in the environment. As most of the transformation processes usually involve a redox reaction or a hydrolysis as the first steps of the transformation, we applied an approach that uses an electrochemical cell to investigate model “redox” reactions in aqueous solutions for environmental processes. We investigated the degradation of a variety of xenobiotics from polar to nonpolar and analyzed their degradation products by on-line coupling of electrochemistry with mass spectrometry (EC–MS). Furthermore, we evaluated possible binding reactions with regard to the generation of non-extractable residues with some model substances (catechol, phthalic acid, γ- -Glutamyl- -cysteinyl-glycine (GSH) and -histidine) deduced from a natural organic matter (NOM) structure model and identified possible binding-sites. Whereas typically investigations in soil/water-systems have been applied, we used to our knowledge for the first time a bottom-up approach, starting from the chemicals of interest and different model substances for natural organic matter to evaluate chemical binding mechanisms (or processes) in the EC–MS under redox conditions. Under oxidative conditions, bindings of the xenobiotics with catechol, GSH and histidine were found, but no reactions with the model compound phthalic acid were observed. In general, no chemical binding has yet been found under reductive conditions. In some cases (i.e. benzo[a]anthracene) the oxidation product only underwent a binding reaction, whereas the xenobiotic itself did not undergo any reactions. EC–MS is a promising fast and simple screening method to investigate the environmental behavior of xenobiotics and to evaluate the potential risks of newly synthesized substances.
    Keywords: Xenobiotics ; Chemical Transformation ; Natural Organic Matter (Nom) ; Electrochemical Simulation ; Mass Spectrometry ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 4
    Language: English
    In: Water Research, 2010, Vol.44(4), pp.1288-1296
    Description: A study was conducted to understand the role of cell concentration and metabolic state in the transport and deposition behaviour of with and without substrate addition. Column experiments using the short-pulse technique (pulse was equivalent to 0.028 pore volume) were performed in quartz sand operating under saturated conditions. For comparison, experiments with microspheres and inactive (killed) bacteria were also conducted. The effluent concentrations, the retained particle concentrations and the cell shape were determined by fluorescent microscopy. For the transport of metabolically-active without substrate addition a bimodal breakthrough curve was observed, which could be explained by the different breakthrough behaviour of the rod-shaped and coccoidal cells of . The 70:30 rod/coccoid ratio in the influent drastically changed during the transport and it was about 20:80 in the effluent and in the quartz sand packing. It was assumed that the active rod-shaped cells were subjected to shrinkage into coccoidal cells. The change from active rod-shaped cells to coccoidal cells could be explained by oxygen deficiency which occurs in column experiments under saturated conditions. Also the substrate addition led to two consecutive breakthrough peaks and to more bacteria being retained in the column. In general, the presence of substrate made the assumed stress effects more pronounced. In comparison to microspheres and inactive (killed) bacteria, the transport of metabolically-active bacteria with and without substrate addition is affected by differences in physiological state between rod-shaped and the formed stress-resistant coccoidal cells of .
    Keywords: Bacteria Transport ; Colloid Deposition ; Cell Morphology ; Physiological State ; Pseudomonas Fluorescens ; Oxygen Stress ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 5
    Language: English
    In: Water Research, 01 February 2013, Vol.47(2), pp.933-944
    Description: Water-saturated column experiments were conducted to investigate the effect of input concentration ( ) and sand grain size on the transport and retention of low concentrations (1, 0.01, and 0.005 mg L ) of functionalized C-labeled multi-walled carbon nanotubes (MWCNT) under repulsive electrostatic conditions that were unfavorable for attachment. The breakthrough curves (BTCs) for MWCNT typically did not reach a plateau, but had an asymmetric shape that slowly increased during breakthrough. The retention profiles (RPs) were not exponential with distance, but rather exhibited a hyper-exponential shape with greater retention near the column inlet. The collected BTCs and RPs were simulated using a numerical model that accounted for both time- and depth-dependent blocking functions on the retention coefficient. For a given , the depth-dependent retention coefficient and the maximum solid phase concentration of MWCNT were both found to increase with decreasing grain size. These trends reflect greater MWCNT retention rates and a greater number of retention locations in the finer textured sand. The fraction of the injected MWCNT mass that was recovered in the effluent increased and the RPs became less hyper-exponential in shape with higher due to enhanced blocking/filling of retention locations. This concentration dependency of MWCNT transport increased with smaller grain size because of the effect of pore structure and MWCNT shape on MWCNT retention. In particular, MWCNT have a high aspect ratio and we hypothesize that solid phase MWCNT may create a porous network with enhanced ability to retain particles in smaller grain sized sand, especially at higher . Results demonstrate that model simulations of MWCNT transport and fate need to accurately account for observed behavior of both BTCs and RPs. ► Breakthrough curves and retention profiles were measured and numerically modeled. ► We used very low (0.005–1 mg L ) input concentrations of carbon nanotubes (CNTs). ► Breakthrough of CNTs increased with increasing input concentration and grain size. ► Data were simulated well using time- and depth-dependent retention coefficients. ► Model predictions indicate the transport of CNTs to distances greater than 12 cm.
    Keywords: Carbon Nanotubes ; Column Experiments ; Quartz Sand ; Breakthrough Curves ; Retention Profiles ; Transport Modeling ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 6
    Language: English
    In: Chemosphere, 2011, Vol.84(4), pp.409-414
    Description: ► The sorption of a branched nonylphenol isomer (NP111) on humic acids was investigated by a dialysis technique. ► Humic acids were characterized by solid-state C DP/MAS NMR spectroscopy. ► A relationship between the organic carbon-normalized sorption coefficients of NP111 and the aliphaticity of humic acids was established. By using dialysis equilibrium experiments, the sorption of a branched nonylphenol isomer [4-(1-ethyl-1,3-dimethylpentyl)-phenol] (NP111) on various humic acids (HAs) isolated from river sediments and two reference HAs was studied. The HAs were characterized by solid-state C direct polarization/magic angle spinning nuclear magnetic resonance ( C DP/MAS NMR) spectroscopy. Sorption isotherms of NP111 on HAs were described by a linear model. The organic carbon-normalized sorption coefficient ( ) ranged from 2.3 × 10 to 1.5 × 10 L kg . Interestingly, a clear correlation between value and alkyl C content was observed, indicating that the aliphaticity of HAs markedly dominates the sorption of NP111. These new mechanistic insights about the NP111 sorption indicate that the fate of nonylphenols in soil or sediment depends not only on the content of HA, but also on its structural composition.
    Keywords: Branched Nonylphenol ; Sorption ; Humic Acids ; NMR ; Aliphaticity ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 7
    Language: English
    In: Water Research, 01 February 2017, Vol.109, pp.358-366
    Description: Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L ) of functionalized C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca in comparison to K , and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca in comparison to K . Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K displaced Ca ) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that 〉23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca than K . These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs.
    Keywords: Multi-Walled Carbon Nanotubes ; Soil ; Breakthrough Curves ; Retention Profiles ; Cation Exchange ; Soil Fractionation ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 8
    Language: English
    In: Science of the Total Environment, 01 December 2015, Vol.535, pp.102-112
    Description: It is considered inevitable that the increasing production and application of engineered nanoparticles will lead to their release into the environment. However, the behavior of these materials under environmentally relevant conditions is still only poorly understood. In this study the transport and deposition behavior of engineered surfactant stabilized silver nanoparticles (AgNPs) in water saturated porous media was investigated in transport experiments with glass beads as reference porous medium and in two natural soils under various hydrodynamic and hydrochemical conditions. The transport and retention processes of AgNPs in the porous media were elucidated by inverse modeling and possible particle size changes occurring during the transport through the soil matrix were analyzed with flow field-flow fractionation (FlFFF). A high mobility of AgNPs was observed in loamy sand under low ionic strength (IS) conditions and at high flow rates. The transport was inhibited at low flow rates, at higher IS, in the presence of divalent cations and in a more complex, fine-grained silty loam. The slight decrease of the mean particle size of the AgNPs in almost all experiments indicates size selective filtration processes and enables the exclusion of homoaggregation processes.
    Keywords: Engineered Nanoparticle ; Soil ; Transport and Retention ; Transport Modeling ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 9
    Language: English
    In: Water research, 2010, Vol.44, pp.1288-1296
    Description: In the special issue: Transport and Fate of Colloids and Microbes in Granular Aqueous Environments / Edited by David Dixon, Nathalie Tufenkji and Monica B. Emelko. Includes references ; p. 1288-1296.
    Keywords: Pseudomonas Fluorescens ; Colloids ; Oxygen ; Microbial Contamination ; Porous Media ; Metabolism ; Drinking Water ; Saturated Conditions
    ISSN: 0043-1354
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 10
    Language: English
    In: Environmental Pollution, Sept, 2013, Vol.180, p.152(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.envpol.2013.05.031 Byline: Daniela Kasel, Scott A. Bradford, JiAi A imA[macron]nek, Thomas Putz, Harry Vereecken, Erwin Klumpp Abstract: Column experiments were conducted in undisturbed and in repacked soil columns at water contents close to saturation (85-96%) to investigate the transport and retention of functionalized.sup.14C-labeled multi-walled carbon nanotubes (MWCNT) in two natural soils. Additionally, a field lysimeter experiment was performed to provide long-term information at a larger scale. In all experiments, no breakthrough of MWCNTs was detectable and more than 85% of the applied radioactivity was recovered in the soil profiles. The retention profiles exhibited a hyper-exponential shape with greater retention near the column or lysimeter inlet and were successfully simulated using a numerical model that accounted for depth-dependent retention. In conclusion, results indicated that the soils acted as a strong sink for MWCNTs. Little transport of MWCNTs is therefore likely to occur in the vadose zone, and this implies limited potential for groundwater contamination in the investigated soils. Author Affiliation: (a) Agrosphere Institute (IBG-3), Forschungszentrum Julich GmbH, 52425 Julich, Germany (b) US Salinity Laboratory, Agricultural Research Service, United States Department of Agriculture, Riverside, CA 92507, USA (c) Department of Environmental Sciences, University of California Riverside, Riverside, CA 92521, USA Article History: Received 8 February 2013; Revised 8 May 2013; Accepted 16 May 2013
    Keywords: Groundwater -- Analysis ; Soils -- Analysis ; Recharge Zones -- Analysis ; Vadose Zone -- Analysis ; Nanotubes -- Analysis ; Soil Carbon -- Analysis
    ISSN: 0269-7491
    Source: Cengage Learning, Inc.
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