Assessment of Progress - Research Progress on Environmental Health and Safety Aspects of Engineered Nanomaterials - page 23

substantial progress has been made in developing analytic tools and methods for detecting and
characterizing nanomaterials. (Detection and characterization of ENMs in more complex environmental
media are discussed later in this chapter.) Several agencies—including NIST, the US Army Corps of
Engineers Engineer Research and Development Center, and the NCL—have active research programs in
place that are aimed at developing and validating the tools (NSET 2012a). Some components of activities
in two research centers funded by the Environmental Protection Agency (EPA) and the National Science
Foundation (NSF) are aimed at developing and validating ENM detection and characterization methods;
in most cases, these are applications of, or adaptations of, existing tools, including x-ray spectroscopy
(Ma et al. 2012; Lawrence et al. 2012), spectrometry (Mitrano et al. 2012), and optical methods (Fatisson
et al. 2012). Some new methods are being developed to measure important ENM properties, such as
surface hydrophobicity of nanoparticles (Xiao and Wiesner 2012) and chirality of single-walled CNTs
(Khan et al. 2013). In addition, the nanotechnology EHS research community now recognizes the
dynamic nature of nanomaterials and the need to characterize nanomaterial transformations and the
transformed materials (Levard et al. 2012; Liu et al. 2012; Lowry et al. 2012a; Nowack et al. 2012).
The committee classifies this indicator as green because of the number of programs initiated or
under way in various agencies and the progress evident in the peer-reviewed literature (as described
above). However, characterization efforts are generally (not exclusively) limited to studies in well-
controlled model media, and more work is needed to extend understanding to more complex systems
(discussed later in this chapter). Some ENM properties are still difficult to measure, such as the properties
of adsorbed macromolecules and the structure of the outer surface layers of nanomaterials. Techniques for
routine monitoring of nanomaterials in environmental media (for example, wastewater treatment-plant
effluent) are not available (as discussed later). Finally, although there are many data on ENM
characteristics and likely transformations, cross-validation and synthesis of the data to provide knowledge
about ENM properties and the environmental properties that lead to the transformations have not
occurred.

 Development of methods to quantify effects of nanomaterials in experimental systems

The committee's first report identified the need for standardized methods for assessing
environmental effects of nanomaterials in the environment and the need for markers for assessing
toxicity. It also identified a lack of information on effects, especially ecosystem effects, of longer-term
nanomaterial exposures of organisms and human populations. Studies have been published on the
potential effects of acute nanomaterial exposures of various organisms in aquatic and terrestrial
environments. However, it is difficult to integrate the data to develop the information needed to predict
the effects of ENMs, because of the lack of standardized assays, the variety of ENMs, the variety of
organisms and experimental conditions used, and the fact that many studies have examined primarily
acute mortality outcomes. More toxicity information on a greater variety of nanomaterials is needed so
that different ENM properties and different end points can be examined. Standardization of assays and
development of reference materials for positive and negative controls are also needed to ensure that the
data gathered for toxicity assays are comparable and useful.
The EPA, the Food and Drug Administration (FDA), and the National Institute for Occupational
Safety and Health (NIOSH) have not identified assays targeted at specific outcomes to assess
nanotoxicity. There is a need to standardize toxicity assays, both in vitro and in vivo, to reduce variability
within and between laboratories and to improve consistency of results among different laboratories. For
example, a round-robin in vitro study involving 10 laboratories in the United States and Europe to
characterize nanoparticles before toxicity testing revealed that although there was improved
reproducibility between laboratories because of adherence to strict protocols for shipping, measurement,
and reporting, measurements of polydisperse suspensions of nanoparticle aggregates or agglomerates
were not reproducible (Roebben et al. 2011). The use of ultrasonication increased variability among
polydisperse suspensions. With respect to quantifying effects of nanomaterials in vivo, a 2013 round-
robin study (Bonner et al. 2013) by four laboratories in the United States investigating pulmonary