Nanoscale Reference Materials for Environmental, Health, and Safety Measurements: Needs, Gaps, and Opportunities
Aleksandr B. Stefaniak, Vincent A. Hackley, Gert Roebben, Kensei Ehara, Steve Hankin, Michael T. Postek, Iseult Lynch, Wei-En Fu, Thomas P. Linsinger, Andreas Th?nemann
There is a need to understand and manage potential risks posed to workers, the public, and the environment from exposure to engineered nanomaterials. In response, several organizations have developed lists of relevant nano-objects and of physico-chemical properties thought to be important for the risk assessment of nano-objects. In this paper, we critically review these lists and discuss metrological challenges associated with 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) were common to all lists. Twenty eight lists were identified that contained 51 different properties perceived as important for characterization; (specific) surface area was the only property on all lists. Many of the listed properties were ill-defined or qualitative in nature which precludes development of RMs for these properties. Among the properties that were accurately described and quantitative, many are method-defined, i.e., dependent upon the measurement process. Because of the metrological challenges associated with these method-defined properties, very few nanoscale RMs are currently available, except for particle size measurement. Opportunities exist for the metrology and environmental, health and safety communities to clarify the relationship between nano-object and characterization requirements for safety testing and the concept of RMs. Improved communication and collaboration between these communities may help to clarify which RMs are needed to support the safety assessment of relevant nano-objects or which non-RMs would fulfill needs for safety testing. Such an approach would permit efficient development of more costly RMs to solve specific measurement problems.