title: Influence of Water Hardness on Silver Ion and Silver Nanoparticle Fate and Toxicity TowardNitrosomonas europaea.
abstract: This study investigated the influence of water hardness (Mg2+and Ca2+) on the fate and toxicity of 20 nm citrate silver nanoparticles (AgNPs) and Ag+towardNitrosomonas europaea, a model ammonia-oxidizing bacterium. Nitrification inhibition ofN. europaeaby 1 ppm AgNPs and 0.5 ppm Ag+was reduced from 80% and 83%, respectively, in the absence of Mg2+to 2% and 33%, respectively, in the presence of 730 μM Mg2+. Introduction of Mg2+resulted in the rapid aggregation of the AgNP suspensions and reduced the 3 h Ag+dissolution rates from 30%, in the absence of Mg2+, to 9%, in the presence of 730 μM Mg2+. Reduced AgNP dissolution rates resulted in decreased concentrations of silver that were found adsorbed toN. europaeacells. Increasing AgNP concentrations in the presence of Mg2+increased the observed inhibition of nitrification, but was always less than what was observed in the absence of Mg2+. The presence of Mg2+also reduced the adsorption of Ag+to cells, possibly due to multiple mechanisms, including a reduction in the negative surface charge of theN. europaeamembrane and a competition between Mg2+and Ag+for membrane binding sites and transport into the cells. Ca2+demonstrated similar protection mechanisms, as Ag+toxicity was reduced and AgNP suspensions aggregated and decreased their dissolution rates. These results indicate that the toxicity of Ag+and AgNPs to nitrifying bacteria in wastewater treatment would be less pronounced in systems with hard water.
authors: School of Chemical, Biological and Environmental Engineering, Oregon State University , Corvallis, Oregon.
authors: Joseph W
authors: JW
authors: Anderson
authors: School of Chemical, Biological and Environmental Engineering, Oregon State University , Corvallis, Oregon.
authors: Lewis
authors: L
authors: Semprini
authors: School of Chemical, Biological and Environmental Engineering, Oregon State University , Corvallis, Oregon.
authors: Tyler S
authors: TS
authors: Radniecki
keywords: Nitrosomonas europaea; adsorption; magnesium; silver ions; silver nanoparticles; toxicity