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.
- SourceAvailable from: Sushil Raj Kanel
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- "When NOM interacts with AgNPs, there may be charge and steric effects that can influence the fate, transport, and toxicity of these AgNPs (Fabrega et al. 2009). A number of recent studies have examined the transport of unmodified and surface-modified AgNPs in saturated porous media (e.g., unmodified AgNPs (Lin et al. 2011), citrate-stabilized AgNPs (El Badawy 2011; Sagee et al. 2012; Taghavy et al. 2013), polyvinylpyrrolidone (PVP)-AgNPs (El Badawy et al. 2011; Flory et al. 2013; Lin et al. 2012b; Mitzel and Tufenkji 2014; Sagee et al. 2012; Song et al. 2011), Gum Arabic-AgNPs (Lin et al. 2012a; Song et al. 2011), branched polyethyleneimine-coated AgNPs (El Badawy 2011), and proteinate-AgNPs (Ren and Smith 2013). These studies have reported the effect of flow velocity, pH, and ionic strength on AgNP transport. "
ABSTRACT: Understanding the fate and transport of silver nanoparticles (AgNPs) is of importance due to their widespread use and potential harmful effects on humans and the environment. The present study investigates the fate and transport of widely used Creighton AgNPs in saturated porous media. Previous investigations of AgNP transport in the presence of natural organic matter (NOM) report contradictory results regarding how the presence of NOM affected the stability and mobility of AgNPs. In this work, a nonreactive tracer, AgNPs and a mixture of AgNPs and NOM were injected into a background solution (0.01 mM of NaNO3) flowing through laboratory columns packed with water-saturated glass beads to obtain concentration versus time breakthrough curves. Transport of AgNPs in the presence of NOM was simulated with a model that accounted for both reversible and irreversible attachment. Based upon an analysis of the AgNP breakthrough curves, it was found that addition of NOM at concentrations ranging from 1 to 40 mg L−1 resulted in significant decreases in both the zeroth and first moments of the breakthrough curves. These observations may be attributed to NOM promoting AgNP aggregation and irreversible attachment. Raman and surface-enhanced Raman scattering analysis of NOM-AgNP mixtures revealed that a possible interaction of NOM with AgNP occurred through the carboxylic moieties (–COO−) located in the immediate vicinity of the metallic surface. At higher concentrations of NOM, both the zeroth and first moments of the breakthrough curves increased. Based on modeling and the literature, we hypothesize that as the NOM concentration increases, it begins to coat both the AgNPs and the glass beads, leading to a situation where AgNP transport may be described in the same way that transport of a sorbing hydrophobic compound partitioning to an immobile organic phase is typically described, assuming reversible, rate-limited sorptionJournal of Nanoparticle Research 03/2015; 17(3):1-13. DOI:10.1007/s11051-015-2956-y · 2.28 Impact Factor
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- "There was a better relationship between AgNM toxicity and clay content, with only small deviations (05G and 02A). The retention of AgNMs in natural soil has previously been shown to increase in line with the granulometric clay content (Cornelis et al., 2012; Sagee et al., 2012 "
ABSTRACT: a b s t r a c t We investigated the effects of silver nanomaterials (AgNMs) on five well-characterized soils with distinct physicochemical properties using two standardized test systems. The carbon transformation test (OECD 217) showed minimal sensitivity whereas the ammonia oxidizing bacteria test (ISO 15685) showed extreme sensitivity over 28 days of exposure. AgNM toxicity was compared with the physicochemical properties of the soils, revealing that toxicity declined with increasing clay content and increasing pH. AgNM toxicity did not appear to be affected by the organic carbon content of the soil. Our results showed that AgNM toxicity cannot be attributed to any single soil property but depends on the same parameters that determine the toxicity of conventional chemicals. Recommendations in the test guidelines for soil ecotoxicity studies are therefore applicable to AgNMs as well as conventional chemicals. article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Environmental Pollution 01/2015; 196:321 - 330. DOI:10.1016/j.envpol.2014.10.021 · 3.90 Impact Factor
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- "However, conclusions drawn from these studies may have only limited relevance to natural soils that are highly complex and heterogeneous in terms of physicochemical properties such as variable composition (e.g., presence of clay minerals and metal oxides) and natural organic matter (NOM) coating, broad particle size distribution, complex pore structure, and pronounced surface roughness (Cornelis et al., 2012, 2013; Darlington et al., 2009; Fang et al., 2009; Grolimund et al., 1998; Jaisi and Elimelech, 2009; Pan and Xing, 2012; Sagee et al., 2012). Recently, researchers have attempted to explore the mobility of AgNPs in sandy soils with relatively low amounts of clay-size particles (Liang et al., 2013b; Sagee et al., 2012). However, little research has been conducted to investigate the influence of physicochemical factors on the mobility of AgNPs in natural soils that are rich in clay-size particles (diameter b2 μm), largely due to their low hydraulic conductivities (e.g., likely inducing pore clogging) (Grolimund et al., 1998; Jaisi and Elimelech, 2009). "
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. DOI:10.1016/j.jconhyd.2014.05.007 · 2.70 Impact Factor