Assessment of Progress - Research Progress on Environmental Health and Safety Aspects of Engineered Nanomaterials - page 22

T he committee's first report emphasized that libraries of well-characterized nanomaterials were
needed to accelerate EHS nanotechnology research and that the libraries should include nanomaterials
that meet the evolving needs of the research community. There has been progress in developing specific
nanomaterials that have been appropriately characterized for nanotechnology EHS studies, including
gold, silver, and carbon standards developed by the National Institute of Standards and Technology (NIST
2013a), Organisation for Economic Co-operation and Development reference materials characterized by
the National Institutes of Health (NIH) Nanotechnology Characterization Laboratory (NCL) for the
National Institute of Environmental Health Sciences Nanotechnology Consortium (AZoNano.com 2010),
and materials developed in individual research groups and centers. Some of those materials are now
available through commercial channels (NanoComposix 2012). However, the composition, structure,
properties, impurities, and contaminants of a nanomaterial sample depend on the production, refinement,
separation, and purification processes used to make them and can exhibit substantial lot-to-lot variation.
In addition, the sample-preparation techniques used for different characterization methods are generally
not well documented or reported. For example, the NCL reports (McNeil 2012) that up to 40% of samples
submitted to it for characterization were contaminated with endotoxin even though they had been vetted
for possible use in therapeutics. It will continue to be difficult to correlate published research results with
nanomaterial types unless more detail is provided in publications or documentation of datasets regarding
the manufacturing process, lot number, and sample-preparation and characterization methods used.
For the last few years, it has been recognized that nanomaterials for EHS research need to be well
characterized in the media in which they are used (Richman and Hutchison 2009; von der Kammer et al.
2012; Pettit and Lead 2013). Although there has been progress in that respect (for example, use of the
same well-characterized materials in various studies to allow comparison of results), there still are no
recommended standard materials for characterization. Nanomaterials produced for fundamental or applied
research are rarely characterized adequately for EHS research. Therefore, new nanomaterials that are
produced and developed for applied research typically cannot be used more broadly for EHS research,
because of the different types of characterization needed, which depend on the intended uses.
With respect to developing materials libraries to support nanotechnology EHS research, the
committee concludes that much work is needed. There has been an emphasis on nanomaterials that have
been documented to be most prevalent in commerce—including nanosilver, carbon nanotubes (CNTs),
and zinc oxide (ZnO) (OECD 2008; PEN 2013)—although a recent survey of the patent literature
suggests that there is probably a more diverse set of materials that are being and will be incorporated into
products (Leitch et al. 2012). To accelerate research, a larger set of nanomaterials is needed to identify the
structural features responsible for potential biologic and environmental effects. Specifically, ENMs
should be selected to address hypotheses regarding the influences of individual structural parameters (for
example, surface coating, surface functionality, ion release rates from core material, core sizes, and
material purity). Thus far, there has been little progress in producing structurally analogous sets (or
libraries) of well-characterized nanomaterials (Harper et al. 2011). As a result, it is not possible to
conduct systematic studies of families of structurally related nanomaterials to determine how structure
influences effects. Not surprisingly, the structural diversity of the materials that have been produced does
not yet support the needed breadth of nanotechnology EHS studies.
Thus, although there has been some progress in producing and characterizing new nanomaterials
to support EHS research, there are large gaps, and progress toward this goal is categorized as yellow.
 Development of methods for detecting, characterizing, tracking, and monitoring nanomaterials
and their transformations in simple, well-characterized media
In its first report, the committee gave high priority to research that promotes development of
critical supporting tools, including methods of characterizing how the properties of ENMs affect their
interactions with humans and the environment (NRC 2012). Those capabilities need to be developed in
the short term and ramped up to become sustainable in the longer term. In simple and relatively well-
characterized media (such as deionized water and physiologic buffer with known composition),