title: The fate of silver nanoparticles in soil solution--Sorption of solutes and aggregation.
abstract: Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254 nm, and the absorption ratio α254/α410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca(2+) solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320 μg/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag(+) ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces.
authors.affiliation: Freiburg University, Institute of Forest Sciences, Chair of Soil Ecology, D-79085 Freiburg, Germany; Berlin University of Technology, Institute of Ecology, Department of Soil Science, Ernst-Reuter-Platz 1, D-10587 Berlin, Germany. Electronic address: Sondra.klitzke@alumni.tu-berlin.de.
authors.forename: Sondra
authors.initials: S
authors.lastname: Klitzke
authors.affiliation: University Koblenz-Landau, Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, Fortstr. 7, D-76829 Landau, Germany. Electronic address: metreveli@uni-landau.de.
authors.forename: George
authors.initials: G
authors.lastname: Metreveli
authors.affiliation: Berlin University of Technology, Institute of Ecology, Department of Soil Protection, Ernst-Reuter-Platz 1, D-10587 Berlin, Germany. Electronic address: Andre.peters@tu-berlin.de.
authors.forename: Andre
authors.initials: A
authors.lastname: Peters
authors.affiliation: University Koblenz-Landau, Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, Fortstr. 7, D-76829 Landau, Germany. Electronic address: schaumann@uni-landau.de.
authors.forename: Gabriele E
authors.initials: GE
authors.lastname: Schaumann
authors.affiliation: Freiburg University, Institute of Forest Sciences, Chair of Soil Ecology, D-79085 Freiburg, Germany. Electronic address: fritzi.lang@bodenkunde.uni-freiburg.de.
authors.forename: Friederike
authors.initials: F
authors.lastname: Lang
mesh_terms: D053768:Metal Nanoparticles / Q000032:analysis* / Q000737:chemistry; D008956:Models, Chemical; D012834:Silver / Q000032:analysis* / Q000737:chemistry; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D012996:Solutions
chemical_list: D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; D012834:Silver
keywords: Cation valency; Exchangeability of sorbed Ag ions; Initial nanoparticle concentration; Isoelectric point