Applications of Low Energy Microfocused X-Ray Microprobe Technique for Assessing the Chemical Fate of Nanosilver in Soils.

Antimicrobial effects of silver nanoparticles (AgNPs) have been extensively investigated in in aquatic systems in the past decades. However, it remains a difficult task to extrapolate the toxicological data to the terrestrial environment since the fate of AgNPs in heterogeneous soils still poorly understood. To improve our understanding of AgNP toxicity in the terrestrial environment, the effects of AgNPs (15-50 nm, with and without polyvinylpyrrolidone (PVP) coating) on soil nitrification and denitrification processes were recently investigated. The results suggested the toxicity might be depending on the particle specific phase transformation of AgNPs. Linear combination (LC) of reference compound fit analysis on bulk Ag K-edge XAS spectra showed that some particles transformed into Ag₂S and or humic acid (HA) complexed Ag(I). While the results of LC analysis showed an importance of sulfur geochemistry in assessing the fate of AgNPs in soils, there has not been any direct evidence showing the correlation of Ag with S. In this study, the results of low energy microfocused-X-ray microprobe analysis including Ag L₃-edge XAS measurements will be discussed. The results of this study should highlight the sulfur geochemistry in predicting the fate of AgNPs and or Ag(I)(aq) in soils, and could potentially help to model the biogeochemical behavior of soft acid based  nanoparticles in terrestrial environments.