The overall hypothesis of our work is that the bioavailability of nanoscale materials in the aquatic environment is linked to multiple transformation pathways for the nanomaterials (dissolution, aggregation, and surface modifications). In the silver work, we test silver nanomaterials synthesized with two types of coatings (citrate or PVP) and found that a Ag+-binding ligand, such as cysteine, increase the solubility of silver in suspension. The dissolution rate depended on the aggregation state of the nanoparticles (modified by a monovalent electrolyte). Furthermore, the cysteine directly modified the nanoparticles, resulting in the formation of monovalent Ag-cysteine coordination on the particle surfaces. This research was presented at the Goldschmidt Conference (August 2011, Prague). A manuscript is in preparation.
In the mercury work, we tested the bioavailability of HgS nanoparticles to bacteria that convert this mercury to methylmercury. Overall, the results show that the nanoparticle exposure resulted in mercury methylation that was faster than bulk-scale HgS particles and slower than dissolved forms of Hg. We believe that enhanced methylation of nano-HgS (over micro-HgS) was due to the amorphous nature of the nanoparticles that increased their solubility in the bacteria culture media. This result provides an example of how nanoscale materials in nature can have distinct bioavailability to microbes that are not the same as bulkscale mineral. This paper was presented at Goldschmidt and the International Conference on Mercury as a Global Pollutant (July 2011, Halifax).