Nanoscale reference materials for environmental, health and safety measurements: needs, gaps and opportunities

Abstract

The authors critically reviewed published lists of nano-objects and their physico-chemical properties deemed important for risk assessment and discussed metrological challenges associated with the development of nanoscale reference materials (RMs). Five lists were identified that contained 25 (classes of) nano-objects; only four (gold, silicon dioxide, silver, titanium dioxide) appeared on all lists. Twenty-three properties were identified for characterisation; only (specific) surface area appeared on all lists. The key themes that emerged from this review were: 1) various groups have prioritised nano-objects for development as "candidate RMs" with limited consensus; 2) a lack of harmonised terminology hinders accurate description of many nano-object properties; 3) many properties identified for characterisation are ill-defined or qualitative and hence are not metrologically traceable; 4) standardised protocols are critically needed for characterisation of nano-objects as delivered in relevant media and as administered to toxicological models; 5) the measurement processes being used to characterise a nano-object must be understood because instruments may measure a given sample in a different way; 6) appropriate RMs should be used for both accurate instrument calibration and for more general testing purposes (e.g., protocol validation); 7) there is a need to clarify that where RMs are not available, if "(representative) test materials" that lack reference or certified values may be useful for toxicology testing and 8) there is a need for consensus building within the nanotechnology and environmental, health and safety communities to prioritise RM needs and better define the required properties and (physical or chemical) forms of the candidate materials.

The Current World of Nanomaterial Characterization: Discussion of Analytical Instruments for Nanomaterial Characterization

“…As a result, the range of nanomaterial parameters that have to be assessed to characterize nanomaterials is large (Salamon et al, 2010). Aleck Stefaniak has ''summarized twenty-three different physio-chemical material properties that were identified as important for NO characterization as part of the risk assessment process collected from published literature'' (Stefaniak et al, 2012). I have chosen to address nine key characteristics that contribute to the uniqueness of nanomaterials, and these are depicted in Fig.…”

Overview of Nanomaterial Characterization and Metrology

“…The importance of proper nanomaterial characterization cannot be understated. Stefaniak et al 5 argues that incomplete nanomaterial characterization limits the reliability (and perhaps validity) of conclusions drawn from scientific investigations, which may impede both future research in and commercialization of nanotechnology. By way of example, a review by Hansen et al 6 of over 400 published nanotoxicology studies concluded that nanomaterial characterization was either poorly described or not at all conducted.…”

Size Distributions

“…24 However, it is clear that great caution must be taken in the measurement, interpretation and reporting of NM size. For example, the lack of an observed effect of size of a given NM on its toxicity may not support a lack of this relationship.…”