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  • 1
    Language: English
    In: Environmental science & technology, 19 August 2014, Vol.48(16), pp.8946-62
    Description: This contribution critically reviews the state of knowledge on interactions of natural colloids and engineered nanoparticles with natural dissolved organic materials (DOM). These interactions determine the behavior and impact of colloids in natural system. Humic substances, polysaccharides, and proteins present in natural waters adsorb onto the surface of most colloids. We outline major adsorption mechanisms and structures of adsorption layers reported in the literature and discuss their generality on the basis of particle type, DOM type, and media composition. Advanced characterization methods of both DOM and colloids are needed to address insufficiently understood aspects as DOM fractionation upon adsorption, adsorption reversibility, and effect of capping agent. Precise knowledge on adsorption layer helps in predicting the colloidal stability of the sorbent. While humic substances tend to decrease aggregation and deposition through electrostatic and steric effects, bridging-flocculation can occur in the presence of multivalent cations. In the presence of DOM, aggregation may become reversible and aggregate structure dynamic. Nonetheless, the role of shear forces is still poorly understood. If traditional approaches based on the DLVO-theory can be useful in specific cases, quantitative aggregation models taking into account DOM dynamics, bridging, and disaggregation are needed for a comprehensive modeling of colloids stability in natural media.
    Keywords: Humic Substances ; Colloids -- Chemistry ; Nanoparticles -- Chemistry ; Water Pollutants, Chemical -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 2
    Language: English
    In: Environmental science & technology, 16 January 2018, Vol.52(2), pp.436-445
    Description: Citrate (Cit) and polyethylenimine (BPEI)-coated silver nanoparticles (AgNPs) were used to understand how the type of capping agents and surface charge affect their colloidal stability, dissolution, and ecotoxicity in the absence/presence of Pony Lake Fulvic Acid (PLFA). In the presence of PLFA, Cit-AgNPs were stabilized, while BPEI-AgNPs were aggregated. The aggregation of BPEI-AgNPs decreased with the time, and their stabilizing effect increased at high PLFA concentration. The dissolution also differed between both AgNPs and was influenced by the PLFA concentration. Generally, BPEI-AgNPs showed a lower amount of dissolved Ag than Cit-AgNPs. The dissolved Ag concentration decreased for both AgNPs at low PLFA concentration (5 mg/L). In contrast, the extent of nanoparticle dissolution increased at high PLFA concentration (30 mg/L) but only for BPEI-AgNPs. In the absence of PLFA, the ecotoxicity of Cit-AgNPs to Daphnia magna was higher than that of BPEI-AgNPs. However, the ecotoxicity of AgNPs in the presence of PLFA was up to 70% lower than in their absence. We demonstrated that the differences in colloidal stability, dissolution, and ecotoxicity may be attributed to the different capping agents, surface charge, and concentration of natural organic matter (NOM) as well as to the formation of dissolved Ag complexes with NOM.
    Keywords: Daphnia ; Metal Nanoparticles
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 3
    Language: English
    In: Environmental science & technology, 21 May 2013, Vol.47(10), pp.5083-91
    Description: The fate of engineered nanoparticles in environmental systems is controlled by changes in colloidal stability and their interaction with different environmental surfaces. Little is known about nanoparticle-surface interactions on the basis of sorption isotherms under quasi-equilibrium conditions, although sorption isotherms are a valuable means of studying sorbate-sorbent interactions. We tested the extent to which the sorption of engineered silver nanoparticles (nAg) from stable and unstable suspensions to model (sorbents with specific chemical functional groups) and environmental (plant leaves and sand) surfaces can be described by classical sorption isotherms. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) qualitative and quantitative analyses were also used to assess the morphology and nanomechanical parameters of the covered surfaces. The sorption of nAg from stable suspensions was nonlinear and best described by the Langmuir isotherm. Langmuir coefficients varied with sorbent surface chemistry. For nAg sorption from an unstable suspension, the sorption isotherms did not follow any classical sorption models, suggesting interplay between aggregation and sorption. The validity of the Langmuir isotherm suggests monolayer sorption, which can be explained by the blocking effect due to electrostatic repulsion of individual nanoparticles. In unstable suspensions, aggregates are instead formed in suspension and then sorbed, formed on the surface itself, or formed in both ways.
    Keywords: Models, Chemical ; Metal Nanoparticles -- Chemistry ; Silver -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 4
    Language: English
    In: Environmental science & technology, 01 October 2011, Vol.45(19), pp.8411-9
    Description: The stabilizing effect of water molecule bridges on polar regions in humic substances (HSs) has been investigated by means of molecular dynamics (MD) simulations. The purpose of these investigations was to show the effect of water molecular bridges (WAMB) for cross-linking distant locations of hydrophilic groups. For this purpose, a tetramer of undecanoid fatty acids connected to a network of water molecules has been constructed, which serve as a model for spatially fixed aliphatic chains in HSs terminated by a polar (carboxyl) group. The effect of environmental polarity has been investigated by using solvents of low and medium polarity in force-field MD. A nonpolar environment simulated by n-hexane was chosen to mimic the stability of WAMB in a hydrophilic hotspot surrounded by a nonpolar environment, while the more polar acetonitrile environment was chosen to simulate a more even distribution of polarity around the carboxylic groups and the water molecules. The dynamics simulations show that the rigidity of the oligomer chains is significantly enhanced as soon as the water cluster is large enough to comprise all four carboxyl groups. Increasing the temperature leads to evaporization processes which destabilize the rigidity of the tetramer-water cluster. Embedding it into the nonpolar environment introduces a pronounced cage effect which significantly impedes removal of water molecules from the cluster region. On the other hand, a polar environment facilitates their diffusion from the polar region. One important consequence of these simulations is that although the local water network is the stabilizing factor for the organic matter matrix, the degree of stabilization is additionally affected by the presence of nonpolar surroundings.
    Keywords: Molecular Dynamics Simulation ; Humic Substances -- Analysis ; Water -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 5
    Language: English
    In: Environmental science & technology, 19 April 2016, Vol.50(8), pp.4278-88
    Description: Concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs) in air and soil, their fugacities, and the experimental soil-air partitioning coefficient (KSA) were determined at two background sites in the Gt. Hungarian Plain in August 2013. The concentrations of the semivolatile organic compounds (SOCs) in the soil were not correlated with the organic carbon content but with two indirect parameters of mineralization and aromaticity, suggesting that soil organic matter quality is an important parameter affecting the sorption of SOCs onto soils. Predictions based on the assumption that absorption is the dominant process were in good agreement with the measurements for PAHs, OCPs, and the low chlorinated PCBs. In general, soils were found to be a source of PAHs, high chlorinated PCBs, the majority of OCPs and PBDEs, and a sink for the low chlorinated PCBs and γ-hexachlorocyclohexane. Diurnal variations in the direction of the soil-air exchange were found for two compounds (i.e., pentachlorobenzene and p,p'-dichlorodiphenyldichloroethane), with volatilization during the day and deposition in the night. The concentrations of most SOCs in the near-ground atmosphere were dominated by revolatilization from the soil.
    Keywords: Air Pollutants -- Analysis ; Pesticides -- Analysis ; Polychlorinated Biphenyls -- Analysis ; Polycyclic Aromatic Hydrocarbons -- Analysis ; Volatile Organic Compounds -- Analysis
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 6
    Language: English
    In: Environmental science & technology, 15 December 2005, Vol.39(24), pp.9534-40
    Description: Until now, glass transitions were detected in isolated humic and fulvic acids as well as in distinct soil samples with usually high Corg contents. The results of this study indicate that glassiness has to be considered a common characteristic of soil organic matter (SOM). However, two types of glassiness were observed in various soil types. Additionally to a typical glass transition with low intensity, a slowly reversing glasstransition-like step transition with significantly higher intensity was detected in 52 out of 102 tested soil samples. The intensity of this transition type is correlated to the organic matter content of the samples. The transition behavior additionally depends on characteristics of the locations and changes within soil profiles. Relations to particulate organic matter (POM), mineral-associated organic matter (MOM), and the thermostable fraction of the soil samples were not significant. A surprising result of the study is that the step transition temperatures of all analyzed air-dried soil samples range between 51 and 67 degrees C in closed systems, pointing to a superordinate mechanism which controls the matrix rigidity of the organic molecules. This may be represented by the formation of hydrogen bond based cross-links between water molecules and SOM suggested in a previous study. Thus, glassiness in SOM may be caused by physical and physicochemical mechanisms.
    Keywords: Carbon -- Chemistry ; Geologic Sediments -- Chemistry ; Organic Chemicals -- Analysis ; Soil -- Analysis ; Soil Pollutants -- Analysis
    ISSN: 0013-936X
    E-ISSN: 15205851
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  • 7
    Language: English
    In: Environmental science & technology, 01 February 2005, Vol.39(3), pp.800-6
    Description: This contribution aims to expand the macromolecular view of fractionated natural organic matter (NOM)to organic matter in whole soils. It focuses on glass transition behavior of whole soil organic matter (SOM) and its interrelation with water through use of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Three processes of structural relaxation related to macromolecular mobility were distinguished. Process I occurs in thermally pretreated and very low water-content samples and corresponds to classic glass transition behavior. Process II occurs in water-containing samples, where water is believed to act as an antiplasticizing agent in the peat at water contents below 12%, causing decreased macromolecular mobility and increased glass transition temperature. We suggestthe formation of hydrogen bond-based cross-links being responsible for this antiplasticizing effect. Process III represents a slow swelling process induced by water uptake with a time constant of swelling in the order of days, with water acting as a plasticizing agent. Results from this work are of particular importance for environmental systems as changes in environmental conditions (e.g., water content, temperature) may induce slow structural relaxation processes in NOM over periods of time ranging from days to weeks. These influences on NOM macromolecular mobility lead to continuous changes in physicochemical properties that may greatly influence sorbate-sorbent interactions in surface and subsurface environments.
    Keywords: Models, Theoretical ; Soil ; Soil Pollutants -- Analysis
    ISSN: 0013-936X
    E-ISSN: 15205851
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