Many toxicity studies show the toxic effect of silver nanoparticles (Ag-NPs). However most of these toxicity studies are not relevant to environmental conditions because they do not consider transformations of Ag-NPs expected in the environment and, therefore, may not be evaluating the environmentally relevant form(s) of the Ag-NPs. In this context, our study focuses on characterizing the corrosion processes Ag-NPs. The most common Ag corrosion product occurs when silver strongly reacts with reduced sulfur ligands to form a silver sulfide corrosion layer. We have investigated the sulfidation of Ag-NPs with the goal of determining how sulfidation affect Ag-NPs properties (Environ. Sci. Technol., DOI: 10.1021/es2007758).
A combination of synchrotron-based X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) has shown the formation of Ag2S despite the presence of the PVP coating. TEM observations show the formation of chain-like structures with Ag2S nano-bridges binding the Ag-NPs. Sulfidation strongly affects Ag-NPs properties in term of surface charge and dissolution rate. Both may affect the behavior of Ag-NPs in soils in term of reactivity, transport, and toxicity. In particularly, the decreases of dissolution rate as a function of sulfide exposure may strongly limit Ag-NPs toxicity because released Ag+ ions are known to be a major factor in the toxicity of Ag-NPs.