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Title: Sensitivity of the transport and retention of stabilized silver nanoparticles to physicochemical factors

item LIANG, YAN - Agrosphere Institute
item Bradford, Scott
item SIMUNEK, JIRI - University Of California
item VEREECKEN, HARRY - Agrosphere Institute
item KLUMPP, ERWIN - Agrosphere Institute

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2013
Publication Date: 2/26/2013
Citation: Liang, Y., Bradford, S.A., Simunek, J., Vereecken, H., Klumpp, E. 2013. Sensitivity of the transport and retention of stabilized silver nanoparticles to physicochemical factors. Water Research. 47(7):2572-2582.

Interpretive Summary: The transport of stabilized silver nanoparticles (AgNPs) in the environment may pose a risk to ecosystem health. The objective of this study was to investigate the influence of various physical (grain size, water velocity, and input concentration) and chemical (solution ionic strength) factors on the transport and retention of AgNPs in saturated sand. Findings from this study demonstrated that the migration of AgNP was very sensitive to a variety of factors, and that the distribution of retained AgNPs in sand systematically evolved in shape with experimental conditions. This information will be of special interest to scientists and engineers concerned with predicting the fate of AgNPs in soil and groundwater environments, but it also improves our fundamental understanding of processes that influence the fate of other nanoparticles such as pathogenic viruses.

Technical Abstract: Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solution ionic strength (IS), and an increase in water velocity, sand grain size, and input concentration (Co). In contrast to conventional filtration theory, retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The experimental BTCs and RPs with uniform or hyperexponential shape were well described using a numerical model that considers time- and depth-dependent retention. The simulated maximum retained concentration on the solid phase (Smax) and the retention rate coefficient (k1) increased with IS and as the grain size and/or Co decreased. The RPs were more hyperexponential in finer textured sand and at lower Co because of their higher values of Smax. Conversely, RPs were nonmonotonic or uniform at higher Co and in coarser sand that had lower values of Smax, and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when Smax was approaching filled conditions. Nonmonotonic RPs had peak concentrations at greater distances in the presence of excess amounts of surfactant, suggesting that competition between AgNPs and surfactant diminished Smax close to the column inlet. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum. However, elimination of the secondary minimum only produced recovery of a small portion (<10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity.