Influence of natural organic matter on fate and transport of silver nanoparticles in saturated porous media: laboratory experiments and modeling

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 NaNO 3 ) 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 sorption.

Continuum-based models and concepts for the transport of nanoparticles in saturated porous media: A state-of-the-science review

“…The first type of detachment typically emerges where the feeding solution into the column inlet is switched from the injecting particle dispersion to the particle-free solution with the same ionic strength and pH (two-phase injection experiments). This is the most common reference to 'detachment' and has been observed for various NP such as NZVI [105,136], carbon nanotubes [172], silica [102], nanoporous silicate [173], and Ag NP [174][175][176] (Table 2). This is also known as re-entrainment and has been observed as dramatically extended BTC tailing which has been observed for a wide variety of colloids [165,167,171,177].…”

Silver nanoparticles in aquatic environments: Physiochemical behavior and antimicrobial mechanisms

“…nanosilver is coated by polymers while the porous medium is not) (Lin et al 2012). A detailed 705 discussion of the transport of nanosilver in porous media is beyond the scope of this review and 706 can be found elsewhere (Flory et al 2013, Goldberg et al 2014, Kanel et al 2015…”

Fate of metallic engineered nanomaterials in constructed wetlands: prospection and future research perspectives

“…Similarly to coating, natural dissolved organic matter (DOM) which attaches on the surface of the ENMs has a stabilizing effect on the ENMs due to which the ENMs are more persistent to aggregation (Gallego-Urrea et al 2014) ( Figure 2). DOM has been shown to cause disaggregation and subsequent decrease in Ag-NP size distribution at concentrations 5 -20 mg/L total organic carbon (TOC) as Suwannee river humic acid (SRHA) and up to 15 mg Ag/L (Fabrega et al 2009;Kanel et al 2015;Metreveli et al 2015). Similarly, the presence of DOM has been shown to have a stabilizing effect on However, there are also contradictory results showing no significant impact of SRHA (2.5 -10 mg TOC/L) on the aggregation state of carbonate-coated Ag-NPs or disaggregation of pre-agglomerated Ag-NPs (Piccapietra et al 2012).…”