title: Transport of engineered nanoparticles in partially saturated sand columns.
abstract: The vadose zone is a critical region controlling fate and transport of contaminants in soils and, ultimately, groundwater. It is therefore important to understand the behavior of engineered nanoparticles (ENPs) in this zone, as a potential group of emerging contaminants. Soil is a significant sink for ENPs; however, only a few studies have considered the fate and transport of ENPs in partially saturated systems, representative of the vadose zone. Here, transport behavior of three commonly used ENPs--gold (Au-NPs), silver (Ag-NPs) and zinc oxide (ZnO-NPs)--is investigated in partially saturated sand columns. High mobilities of Au-NPs and Ag-NPs under different water saturation levels and concentrations were observed. The presence of CaCl2 reduces Ag-NP mobility through chemical interactions, similar to behavior reported in saturated systems. Furthermore, transformation of Ag-NPs in the environment may influence their mobility; aging of Ag-NPs following sulfidation was investigated. The silver sulfide (Ag2S-NPs) remained stable in aqueous suspension, and mobile in the partially saturated sand column. In contrast, the positively-charged ZnO-NPs were completely immobilized in the sand column. Significantly, though, addition of humic acid (HA) to the ZnO-NP suspension reverses particle surface charge and thus increases their mobility. Moreover, remobilization of entrapped ZnO-NPs by HA was demonstrated.
authors.affiliation: Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address: yinon.yecheskel@weizmann.ac.il.
authors.forename: Yinon
authors.initials: Y
authors.lastname: Yecheskel
authors.affiliation: Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Ishai
authors.initials: I
authors.lastname: Dror
authors.affiliation: Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Brian
authors.initials: B
authors.lastname: Berkowitz
keywords: Aging; Gold nanoparticles; Remobilization; Silver nanoparticles; Silver sulfide nanoparticles; Zinc oxide nanoparticles