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|The Persistence and Transformation of Silver Nanoparticles in Littoral Lake Mesocosms Monitored Using Various Analytical Techniques|
There is a potential for silver nanoparticles (AgNPs) to be released into surface waters and thus impact aquatic organisms. However, agglomeration, dissolution, surface modifications and chemical speciation are important processes that may control the toxicity of AgNPs. The purpose of the study was to apply and evaluate various methods for monitoring the persistence and transformation of AgNPs added to littoral lake mesocosms. Analytical methods included total Ag analysis, centrifugal ultrafiltration, cloud point extraction (CPE), single particle inductively coupled plasma mass spectroscopy (spICP-MS), and asymmetric flow field flow fractionation with on-line ICP-MS (AF4-ICP-MS). Analysis of total Ag showed that the levels declined rapidly in the first 12 hours after addition, followed by a slower rate of dissipation over the remainder of the study, with a half-life (t1/2) of ~20 days. Based on the spICP-MS results, there was no evidence of extensive homo-agglomeration of AgNPs. The stability of AgNPs was likely due to the low ionic strength and high concentrations of humic-rich dissolved organic carbon (DOC) in the lake water. Analysis by CPE, spICP-MS, and AF4-ICP-MS all indicated that the concentrations of AgNP decreased over time, and the nanoparticles underwent dissolution. However, the concentrations of dissolved silver, which includes Ag+, were generally below detection limits for analysis by centrifugal ultrafiltration and spICP-MS. It is likely that the majority of free ions being released via dissolution were complexing with natural organic material, such as DOC. This prediction was supported by the appearance of an early eluting peak in the fractograms generated by AF4-ICP-MS analysis. An association with DOC would be expected to reduce the toxicity of Ag+ in natural waters. Overall, we were able to characterize AgNP transformations in natural waters at toxicologically relevant concentrations through the use of multiple analytical techniques that compensate for the limitations of the individual methods.
|EN14064 Accepted 27 May 2014|
|© CSIRO 2014|