Disinfection action of electrostatic versus steric-stabilized silver nanoparticles on E. coli under different water chemistries.

The capping layer stabilizing silver nanoparticles (AgNPs) affects its aggregation, dissolution, and net disinfection action, especially under conditions of varying water composition, such as, pH, ionic strength and organic matter content. Herein, we correlate the silver ion (Ag(+)) release and reactive oxygen species (ROS) generation rates for AgNPs of varying functionalization to their net disinfection coefficient on Escherichia coli, under conditions of differing water chemistries. For electrostatically stabilized citrate-capped AgNPs, the rate of ROS generation, as measured using a fluorescent dye, is found to dominate over that of Ag(+) release, especially for smaller sized AgNP suspensions (~10nm) at low pH (~6.2). For these AgNPs, the ROS disinfection mechanism is confirmed to dominate net disinfection action, as measured by the live/dead assay, especially at low levels of organic matter. Steric stabilization of AgNPs by protein or starch-capped layers enables disinfection through reducing AgNP aggregation and promoting silver dissolution over ROS generation. We suggest the involvement of protons and dissolved oxygen in causing the independent formation of Ag(+) and ROS, regardless of the AgNP capping layer. While protein-capping layers effectively stabilize AgNPs, the generated ROS is likely dissipated by interference with the bulky capping layer, whereas the interference is lower with citrate-capping layers. Steric stabilization of AgNPs enables disinfection within a wide range of water chemistries, whereas effective disinfection can occur under electrostatic stabilization, only at low NaCl (<1 mmol/L) and organic matter (<5 mg/L) levels.

Using expert elicitation to prioritize resource allocation for risk identification for nanosilver.

This article introduces a method to identify risks through expert elicitation, using silver nanotechnology as a case study. Unique features of the method include supplying experts with a list of silver nanotechnology products, and conducting the elicitation in an extended interview format that captures the experts' reasoning. The end result is a series of graphical representations of expert thinking from which high-risk scenarios and knowledge gaps can be reliably inferred. This methodology, combined with other approaches to expert elicitation, can help identify knowledge and oversight gaps, and can be used as part of an adaptive management strategy.