This study is designed to provide the data needed to predict the environmental fate and human health effects of commercially manufactured nanoparticles in aqueous solution. With the widespread development of nanoscience and nanotechnology, nanoparticles represent a potential emerging contaminant. The main objectives of the research are to determine under what environmental conditions do manufactured metal nanoparticles of different size and composition aggregate in solution and under what conditions do metal nanoparticles dissolve? Complementary studies to investigate the fundamental surface properties and surface chemistry of metal nanoparticles will be done as surface properties control both nanoparticle aggregation and dissolution as well as nanoparticle-biological interactions. These data can then be used to predict the environmental fate of commercial nanoparticles and are important in assessing the human health effects associated with these materials.