On the transformation and bio-interaction of nanosilver particles in natural waters: Toxicity implications for aquatic organisms

The fast growth of nanotechnology has stimulated research on the potential impacts of its products on both human health and the environment. Results from studies on nanosilver (nAg) toxicity to aquatic organisms have raised questions as to whether or not the observed toxicity was due to the dissolution of toxic silver ions (Ag+). Most studies to date use simple synthetic waters and do not take in to account the complexity of natural waters. The goal of this dissertation research was to comparatively investigate the behavior and toxicity of nAg in natural and synthetic waters.;A series of batch experiments were conducted to determine the effect of different waters on nAg dispersion, stability, and toxicity in comparison with ionic Ag used as AgNO3. Waters were fully characterized and various techniques were employed to assess the stability and dissolution of nAg suspensions. Data from the above studies were used to help explain results obtained in two toxicity assays using freshwater invertebrates and green algae, which were performed in natural waters, traditional growth media, and synthetic waters amended with model organic compounds.;The findings presented in this dissertation help establish needed correlations between water matrix dependent nAg particle properties and toxicity implications using new methods that allow for good representation of natural aquatic systems. Dissolved organic carbon (DOC) was a clear driver in reduction of negative impacts of nAg to aquatic organisms. Conversely, natural water with moderate ionic strength and low DOC, and depending on the test organism used, showed nAg toxicity trends similar to growth media and in others showed greater toxicity than nAg in growth media. Dissolution results presented here paired with stability results suggest that the toxic impacts observed were not completely due to silver ions released from nAg particles.;The use of natural waters to investigate the fate of nAg remains very limited in peer reviewed literature. Similarly, almost no studies have been published using natural waters as both suspension and growth media for toxicity assays. This research shows that behavior and toxicity of nAg in complex natural waters wouldn't be easily predicted by simple alterations of synthetic waters.