Transport of silver nanoparticles (AgNPs) in soil.
ABSTRACT The effect of soil properties on the transport of silver nanoparticles (AgNPs) was studied in a set of laboratory column experiments, using different combinations of size fractions of a Mediterranean sandy clay soil. The AgNPs with average size of ~30nm yielded a stable suspension in water with zeta potential of -39mV. Early breakthrough of AgNPs in soil was observed in column transport experiments. AgNPs were found to have high mobility in soil with outlet relative concentrations ranging from 30% to 70%, depending on experimental conditions. AgNP mobility through the column decreased when the fraction of smaller soil aggregates was larger. The early breakthrough pattern was not observed for AgNPs in pure quartz columns nor for bromide tracer in soil columns, suggesting that early breakthrough is related to the nature of AgNP transport in natural soils. Micro-CT and image analysis used to investigate structural features of the soil, suggest that soil aggregate size strongly affects AgNP transport in natural soil. The retention of AgNPs in the soil column was reduced when humic acid was added to the leaching solution, while a lower flow rate (Darcy velocity of 0.17cm/min versus 0.66cm/min) resulted in higher retention of AgNPs in the soil. When soil residual chloride was exchanged by nitrate prior to column experiments, significantly improved mobility of AgNPs was observed in the soil column. These findings point to the importance of AgNP-soil chemical interactions as a retention mechanism, and demonstrate the need to employ natural soils rather than glass beads or quartz in representative experimental investigations.
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ABSTRACT: The increasing application of engineered nanoparticles (ENPs) has heightened the concern that these ENPs would eventually be released to the environment and may enter into life cycle of living beings. In this regard, it is essential to understand how these ENPs transport and retain in natural soils because they are considered to be a major repository for ENPs. Herein, transport and retention of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (PVP-AgNPs) were investigated over a wide range of physicochemical factors in water-saturated columns packed with an Ultisol rich in clay-size particles. Higher mobility of PVP-AgNPs occurred at larger soil grain size, lower solution ionic strength and divalent cation concentration, higher flow rate, and greater PVP concentrations. Most breakthrough curves (BTCs) for PVP-AgNPs exhibited significant amounts of retardation in the soil due to its large surface area and quantity of retention sites. In contrast to colloid filtration theory, the shapes of retention profiles (RPs) for PVP-AgNPs were either hyperexponential or nonmonotonic (a peak in particle retention down-gradient from the column inlet). The BTCs and hyperexponential RPs were successfully described using a 1-species model that considered time- and depth-dependent retention. Conversely, a 2-species model that included reversibility of retained PVP-AgNPs had to be employed to better simulate the BTCs and nonmonotonic RPs. As the retained concentration of species 1 approached the maximum solid-phase concentration, a second mobile species (species 2, i.e., the same PVP-AgNPs that are reversibly retained) was released that could be retained at a different rate than species 1 and thus yielded the nonmonotonic RPs. Some retained PVP-AgNPs were likely to irreversibly deposit in the primary minimum associated with microscopic chemical heterogeneity (favorable sites). Transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis suggested that these favorable sites were positively charged sites on montmorillonite edges and goethite surfaces in the soil. Overall, our study highlights that the transport and especially retention of PVP-AgNPs are highly sensitive to the physicochemical factors, but mathematical modeling can accurately predict the fate of these ENPs in porous media which is important for better understanding the fate of these ENPs in point of exit and in the environment.Journal of contaminant hydrology. 06/2014; 164C.
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ABSTRACT: Zinc oxide (ZnO) nanoparticles are one of the most frequently used nanoparticles in industry and hence are likely to be introduced to the groundwater environment. The mobility of these nanoparticles in different aquifer materials has not been assessed. While some studies have been published on the transport of ZnO nanoparticles in individual porous media, these studies do not generally account for varying porous medium composition both within and between aquifers. As a first step towards understanding the impact of this variability, this paper compares the transport of bare ZnO nanoparticles (bZnO-NPs) and capped ZnO nanoparticles, coated with tri-aminopropyltriethoxysilane (cZnO-NPs), in saturated columns packed with glass beads, fine grained sand and fine grained calcite, at near-neutral pH and groundwater salinity levels. With the exception of cZnO-NPs in sand columns, ZnO nanoparticles are highly immobile in all three types of studied porous media, with most retention taking place near the column inlet. Results are in general agreement with DLVO theory, and the deviation in experiments with cZnO-NPs flowing through columns packed with sand is linked to variability in zeta potential of the capped nanoparticles and sand grains. Therefore, differences in surface charge of nanoparticles and porous media are demonstrated to be key drivers in nanoparticle transport.Journal of contaminant hydrology 04/2014; 162-163C:17-26. · 2.01 Impact Factor
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ABSTRACT: Transport behavior and fate of engineered silver nanoparticles (AgNP) in the subsurface is of major interest concerning soil and groundwater protection in order to avoid groundwater contamination of vital resources. Sandstone aquifers are important groundwater resources which are frequently used for public water supply in many regions of the world. The objective of this study is to get a better understanding of AgNP transport behavior in partially fractured sandstones. We executed AgNP transport studies on partially fissured sandstone drilling cores in laboratory experiments. The AgNP concentration and AgNP size in the effluent were analyzed using Flow Field-Flow Fractionation mainly. We employed inverse mathematical models on the measured AgNP breakthrough curves to identify and quantify relevant transport processes. Physicochemical filtration, time dependent blocking due to filling of favorable attachment sites and colloid-facilitated transport were identified as the major processes for AgNP mobility. Physicochemical filtration was found to depend on solute chemistry, mineralogy, pore size distribution and probably on physical and chemical heterogeneity. Compared to AgNP transport in undisturbed sandstone matrix reported in the literature, their mobility in partially fissured sandstone is enhanced probably due to larger void spaces and higher hydraulic conductivity.Journal of Contaminant Hydrology. 01/2014;