Influence of Water Hardness on Silver Ion and Silver Nanoparticle Fate and Toxicity Toward Nitrosomonas europaea.

ABSTRACT: This study investigated the influence of water hardness (Mg(2+) and Ca(2+)) on the fate and toxicity of 20?nm citrate silver nanoparticles (AgNPs) and Ag(+) toward Nitrosomonas europaea, a model ammonia-oxidizing bacterium. Nitrification inhibition of N. europaea by 1?ppm AgNPs and 0.5?ppm Ag(+) was reduced from 80% and 83%, respectively, in the absence of Mg(2+) to 2% and 33%, respectively, in the presence of 730??M Mg(2+). Introduction of Mg(2+) resulted in the rapid aggregation of the AgNP suspensions and reduced the 3?h Ag(+) dissolution rates from 30%, in the absence of Mg(2+), to 9%, in the presence of 730??M Mg(2+). Reduced AgNP dissolution rates resulted in decreased concentrations of silver that were found adsorbed to N. europaea cells. Increasing AgNP concentrations in the presence of Mg(2+) increased the observed inhibition of nitrification, but was always less than what was observed in the absence of Mg(2+). The presence of Mg(2+) also reduced the adsorption of Ag(+) to cells, possibly due to multiple mechanisms, including a reduction in the negative surface charge of the N. europaea membrane and a competition between Mg(2+) and Ag(+) for membrane binding sites and transport into the cells. Ca(2+) 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.

SUBMITTER: Anderson JW 

PROVIDER: S-EPMC4098081 | biostudies-other | 2014 Jul

REPOSITORIES: biostudies-other