Influence of soil porewater properties on the fate and toxicity of silver nanoparticles to Caenorhabditis elegans

Engineered nanoparticles (NPs) entering the environment are subject to various transformations that in turn influence how particles are presented to, and taken up by, organisms. To understand the effect of soil properties on the toxicity of nanosilver to Caenorhabditis elegans, toxicity assays were performed in porewater extracts from natural soils with varying organic matter content and pH using 3-8 nm unfunctionalized silver (Ag 3-8Unf), 52-nm polyvinylpyrrolidone (PVP)-coated Ag NPs (Ag 52PVP), and AgNO3 as ionic Ag. Effects on NP agglomeration and stability were investigated using ultraviolet-visible (UV-vis) spectroscopy and asymmetric flow field-flow fractionation (AF4); Ag+ showed greater overall toxicity than nanosilver, with little difference between the NP types. Increasing soil organic matter content significantly decreased the toxicity of Ag 3-8Unf, whereas it increased that of AgNO3 . The toxicity of all Ag treatments significantly decreased with increasing porewater pH. Dissolution of both NPs in the porewater extracts was too low to have contributed to their observed toxic effects. The UV-vis spectroscopy revealed low levels of agglomeration/aggregation independent of soil properties for Ag 3-8Unf, whereas higher organic matter as well as low pH appeared to stabilize Ag 52PVP. Overall, both soil organic matter content and pH affected NP fate as well as toxicity to C. elegans; however, there appears to be no clear connection between the measured particle characteristics and their effect.C.L. Schultz, A. Lawlor, and D.J. Spurgeon received support from the UK Natural Environment Research Council (NERC) Highlight topic on nanomaterials (NE/N006224/1). C.L. Schultz and V. Puntes were supported by the European Union 7th Framework Programme, Marie Curie Actions, Innovative Training Networks Nanotechnology: Training of Experts in Safety (ITN NanoTOES; PITN-GA-2010-264506). E. Lahive was supported by a joint NERC/US Environmental Protection Agency (USEPA) Transatlantic Initiative for Nanotechnology and the Environment (TINE) grant (NE/H013679/1, RD83457401). D.J. Spurgeon and C. Svendsen received support from National Capability funding through the UK NERC-Centre for Ecology & Hydrology (CEH) Pollution and Environmental Risk Theme and the European Union FP7 project GUIDEnano (CP-FP7 604387). J.M. Unrine was supported by the US National Science Foundation (NSF) and the USEPA under NSF Cooperative Agreement EF-0830093 and DBI-1266252, Center for the Environmental Implications of NanoTechnology (CEINT).Peer reviewe