Effect of material properties on stability of silver nanoparticles in water.

Increased production and use of silver nanoparticles (AgNPs) could potentially lead to their release into the environment. Estimating the exposure to engineered nanomaterials in the environment is essential for assessing their risk. This study examined the aggregation and sedimentation kinetics behaviors of citrate- (Cit-AgNPs) and polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) with three different average sizes in calcium chloride (CaCl2) solutions, emphasizing the effects of particle size and type of coating material on both behaviors. As the ionic strength increased, Cit-AgNPs (stabilized by charge repulsion) aggregated rapidly and settled down, while PVP-AgNPs (stabilized by steric repulsion) did not aggregate, even at an ionic strength of 10 mM CaCl2, due to likely steric hiderance effects of PVP coating. Interestingly, however, PVP-AgNPs sedimented without aggregating within 7 days and this tendency seems to having relevance to the particle size. These results suggest that the particle size and type of coating material play important roles in determining nanoparticle fate and transport.