The persistence of zero-valent silver nanoparticles after their release in the aquatic environment will depend on key transformation processes that include aggregation, dissolution, and surface modifications by thiol-containing ligands that are expected to bind Ag+ in many aquatic settings. These transformations work in concert to determine the persistence of silver nanoparticles in the environment and bioavailability to organisms. Here, we studied how low molecular weight thiols (cysteine, glutathione, and N-acetylcysteine) can alter the surface chemistry, aggregation, and dissolution of silver nanoparticles . We compared silver nanomaterials that were synthesized with two different coatings (citrate or polyvinylpirrolidone) and demonstrated that that when the particles were exposed to an excess of cysteine, up to 47% of the silver had dissolved. The zero-order dissolution rates of the nanomaterials depended on the type of synthetic coating and the extent of aggregation, which decreased the exposed surface area available for release of dissolved silver. We also observed through silver K-edge X-ray absorption spectroscopy that cysteine adsorbed to the particles and formed Ag(I)-sulfhydryl bonds at the surface. This modification of the nanoparticles is expected to drastically influence the long term reactivity of the materials in the aquatic environment and bioavailability to exposed organisms who internalize the materials. Our results stress the need to consider multiple and interlinked transformation processes, and particularly those induced by metal-binding constituents in environmental matrices, for assessing potential hazards and exposure pathways of soluble nanomaterials.

Surface modification of metallic silver nanoparticles by low molecular weight thiols: Implications for solubility, aggregation, and bioavailability

243rd National Meeting (2012)

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