The Role of Water Dispersible Clays in the Transport of Silver Nanoparticles From Terrestrial Ecosystems.

Silver nanoparticles (Ag-np) are used in the widest variety of consumer products and can enter the environment from several sources and pathways. Use and disposal estimates of Ag-np suggest their major point of entry will be to terrestrial ecosystems after being removed as solids from wastewater treatments processes, as it has been shown that biosolids retain between 80 and 99% of Ag-np. It is therefore compelling to investigate the Ag-np environmentally relevant mobility from soils amended with Ag-np containing biosolids (Ag-BS). Water dispersible clays (WDC) have been recognized as a good indicator of the erosion risk of soil colloids by water and a facilitator of contaminants’ transport from terrestrial ecosystems to aquatic systems. Therefore, the objectives of this study were to i) determine the potential for Ag-np transport and surface runoff  through WDC fractions collected from soils amended with Ag-BS, and ii) identify components in WDC fractions that adsorb Ag-np and are therefore potentially responsible for their facilitated transport in soils. To that end, biosolids obtained from a wastewater treatment plant in Lexington, KY were spiked with three forms of silver: 10 nm and 30-50 nm poly(N-vinyl-2-pyrrolidone) or PVP coated Ag-nps (respectively designated as SAg-np and LAg-np), and aqueous AgNO3. After an anaerobic incubation, the biosolids were mixed at a 1:1 ratio with two soils with different physicochemical properties: a Loradale sil (Typic Argiudolls) and a Bradson (Typic Hapludult).  WDC fractions were collected and along with residual soils analyzed for Ag, C, N and S. Additionally, WDC were characterized by X-ray diffraction, thermogravimetric analysis, and scanning and transmission electron microscopy. Preliminary results demonstrated that WDC fractions collected from all treatments were enriched with Ag on a concentration basis, and can therefore play an important role as Ag-np carriers from soils receiving heavy applications of Ag-BS.