Investigation into the Potential Toxicity of Zero-Valent Iron Nanoparticles to a Trichloroethylene-Degrading Groundwater Microbial Community

The microbiological impact of zero-valent iron remediation of groundwater was investigated by exposing a trichloroethylene-degrading anaerobic microbial community to bare and coated iron nanoparticles. Changes in population numbers and metabolic activity were analyzed using qPCR and were compared to those of a blank, negative, and positive control to assess for microbial toxicity. Additionally, these results were compared to those of samples exposed to an equal concentration of iron filings in an attempt to discern the source of toxicity. Statistical analysis revealed that the three iron treatments were equally toxic to total Bacteria and Archaea populations, as compared with the controls. Therefore, toxicity appears to result either from the release of iron ions and the generation of reactive oxygen species, or from alteration of the redox system and the disruption of microbial metabolisms. There does not appear to be a unique nanoparticle-based toxicity

Effect of high gold salt concentrations on the size and polydispersity of gold nanoparticles prepared by an extended Turkevich-Frens method

The Turkevich-Frens synthesis starting conditions are expanded, ranging the gold salt concentrations up to 2 mM and citrate/gold(III) molar ratios up to 18:1. For each concentration of the initial gold salt solution, the citrate/gold(III) molar ratios are systematically varied from 2:1 to 18:1 and both the size and size distribution of the resulting gold nanoparticles are compared. This study reveals a different nanoparticle size evolution for gold salt solutions ranging below 0.8 mM compared to the case of gold salt solutions above 0.8 mM. In the case of Au3+]<0.8 mM, both the size and size distribution vary substantially with the citrate/gold(III) ratio, both displaying plateaux that evolve inversely to Au3+] at larger ratios. Conversely, for Au3+]>= 0.8 mM, the size and size distribution of the synthesized gold nanoparticles continuously rise as the citrate/gold(III) ratio is increased. A starting gold salt concentration of 0.6 mM leads to the formation of the most monodisperse gold nanoparticles (polydispersity index<0.1) for a wide range of citrate/gold(III) molar ratios (from 4:1 to 18:1). Via a model for the formation of gold nanoparticles by the citrate method, the experimental trends in size could be qualitatively predicted:the simulations showed that the destabilizing effect of increased electrolyte concentration at high initial Au3+] is compensated by a slight increase in zeta potential of gold nanoparticles to produce concentrated dispersion of gold nanoparticles of small sizes