Key Factors Controlling the Transport of Silver Nanoparticles in Porous Media

Environmental Science & Technology (Impact Factor: 5.33). 03/2013; 47(9). DOI: 10.1021/es304580r
Source: PubMed


The current study investigated the mobility of four AgNPs stabilized using different capping agents and represent the common stabilization mechanisms as well as surface charging scenarios in reactive and non-reactive porous media. The AgNPs were 1) uncoated H2-AgNPs and citrate coated AgNPs (Citrate-AgNPs) (electrostatically stabilized), 2) polyvinylpyrrolidone coated AgNPs (PVP-AgNPs) (sterically stabilized), and 3) branched polyethyleneimine coated AgNPs (BPEI-AgNPs) (electrosterically stabilized). The porous media were 1) quartz sand (QS), 2) ferrihydrite-coated sand (FcS), and 3) kaolin-coated sand (KcS). The H2-AgNPs and Citrate-AgNPs were readily mobile in QS but significantly retained in FcS and KcS with more deposition achieved in the KcS media. The deposition of the H2-AgNPs and Citrate-AgNPs followed the order of KcS > FcS > QS. The PVP-AgNPs breakthrough occurred more rapid as compared to the H2-AgNPs and Citrate-AgNPs but the deposition of PVP-AgNPs followed the same order of the electrostatically stabilized AgNPs (KcS > FcS > QS). The BPEI-AgNPs were readily mobile regardless of the porous media reactivity. Physicochemical interactions were the dominant filtration mechanism in the majority of the investigated cases but straining played the major role in the deposition of the electrostatically stabilized H2-AgNPs and Citrate-AgNPs in the KcS media. The results highlight the importance of both the stabilization mechanism and capping agent chemistry as key factors governing the transport of AgNPs in the environment.

Download full-text


Available from: Kirk G Scheckel
  • Source
    • "The evaluation of toxicity is complex because the impact of pollutants on soil biota is determined by a combination of physicochemical soil characteristics, the chemical form of the pollutant and the physiological status of the biota (Babich et al., 1980). Fate studies have identified factors that influence the transport of AgNMs in soils (Aiken et al., 2011; Akaighe et al., 2011; Coutris et al., 2012; El Badawy et al., 2013; Sagee et al., 2012). The effect of soil type (Shoults-Wilson et al., 2011b) and ion content in the soil pore water (Schlich et al., 2013a) have been considered in earthworm (Eisenia andrei) reproduction tests, but the soil parameters that affect the toxicity of AgNMs towards soil microorganisms are poorly understood and the role played by soil properties has not been investigated. "
    [Show abstract] [Hide abstract]
    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 (
    Full-text · Article · Jan 2015 · Environmental Pollution
  • Source
    • "However, deviations between experimental observations and CFT predictions have been frequently observed . For instance, blocking (a decreasing rate of deposition with time) (Bradford and Bettahar, 2006; Cullen et al., 2010; El Badawy et al., 2013; Li et al., 2008b; Liang et al., 2013a,b; Lin et al., 2011; Petosa et al., 2013; Schijven and Hassanizadeh, 2000; Taghavy et al., 2013; Torkzaban et al., 2013) or ripening (an increasing rate of deposition with time) (Jiang et al., 2012; Kocur et al., 2013; Sagee et al., 2012; Schijven and Hassanizadeh, 2000) behavior in the breakthrough curves (BTCs) and hyperexponential (a decreasing rate of deposition with distance) (Jiang et al., 2012; Li et al., 2004; Liang et al., 2013a,b; Wang et al., 2011, 2012a,b), uniform (invariant deposition rate) (Liang et al., 2013a), or nonmonotonic (a peak in NPs retention down-gradient from the column inlet) (Bradford et al., 2006; Choy et al., 2008; Cornelis et al., 2013; Li et al., 2006, 2008b; Liang et al., 2013a; Tong et al., 2005) behavior in the retention profiles (RPs) have been extensively documented in colloid/NP transport studies. The hyperexponential RPs have been commonly obtained in NP transport studies because the NPs rapidly aggregate to form large sizes of aggregates and thus preferentially deposit near the column inlet (Jiang et al., 2012; Wang et al., 2011, 2012a,b), whereas little information has been documented pertinent to the nonmonotonic RPs. "
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Jun 2014 · Journal of Contaminant Hydrology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Biochar land application may result in multiple agronomic and environmental benefits (e.g., carbon sequestration, improving soil quality, and immobilizing environmental contaminants). However, our understanding of biochar particle transport is largely unknown in natural environment with significant heterogeneity in solid (e.g., patches of iron oxyhydroxide coating) and solution chemistry (e.g., the presence of natural organic matter), which represents a critical knowledge gap in assessing environmental impact of biochar land application. Transport and retention kinetics of nanoparticles (NPs) from wheat straw biochars produced at two pyrolysis temperatures (i.e., 350 and 550 °C) were investigated in water-saturated sand columns at environmentally relevant concentrations of dissolved humic acid (HA, 0, 1, 5, and 10 mg L-1) and fractional surface coverage of iron oxyhydroxide coatings on sand grains (ω, 0.16, 0.28, and 0.40). Transport of biochar NPs increased with increasing HA concentration, largely because of enhanced repulsive interaction energy between biochar NPs and sand grains. Conversely, transport of biochar NPs decreased significantly with increasing ω due to enhanced electrostatic attraction between negatively charged biochar NPs and positively charged iron oxyhydroxides. At a given ω of 0.28, biochar NPs were less retained with increasing HA concentration due to increased electrosteric repulsion between biochar NPs and sand grains. Experimental breakthrough curves and retention profiles were well described using a two-site kinetic retention model that accounted for Langmuirian blocking or random sequential adsorption at one site. Consistent with the blocking effect, the often observed flat retention profiles stemmed from decreased retention rate and/or maximum retention capacity at a higher HA concentration or smaller ω. The antagonistic effects of HA and iron oxyhydroxide grain-coating imparted on the mobility of biochar NPs suggest that biochar colloid transport potential will be dependent on competitive influences exerted by a number of environmental factors (e.g., natural organic matter and metal oxides).
    Full-text · Article · Apr 2013 · Environmental Science & Technology
Show more