Getting to Green - Research Progress on Environmental Health and Safety Aspects of Engineered Nanomaterials - page 55

released, development of integrated models will be important. Those efforts have been limited by the lack
of resources for conducting long-term fate and transport studies in complex environmental systems, such
as mesocosms, or in in vivo studies. An additional limitation is the absence of a knowledge commons in
which research data from multiple studies can be integrated with other information and model outputs to
be used in these complex, initial models. Some individual efforts were identified, but they lack the
consistency in approaches and interoperability of data that is needed to support effective model
development. The efforts also suffer from a focus on a small number of ENMs, which hinders the
development of more widely applicable predictive models.
Steps to Ensure Progress Toward Validated Models for Nanomaterial Risk
Getting to green in the development of predictive models requires substantial development of
data from mechanistic and complex system studies and characterization of physical properties of a variety
of ENMs in different complex environments. Initial working models will require iterative development as
data emerge. Early outputs of the models can determine future data needs and influence decisions about
experimental approaches and instrumentation needs. Data should be collected with consideration of future
data integration and modeling efforts. Input of the data into a knowledge commons is needed to allow a
wide array of investigators to engage in modeling efforts. Validation studies that use families of materials
in various complex environments will be required. Models for assessing hazard, exposure, and risk will
depend on the data sources, and appropriate information management and integration will help to produce
a more coordinated and focused approach for addressing EHS aspects of ENMs.
METHODS AND INSTRUMENTATION
The need for methods and instrumentation to characterize ENMs in relevant media is pervasive in
the nanotechnology EHS research enterprise. Methods and instrumentation are defined here as the tools
required to detect and to characterize ENMs and their properties in relevant media. Toxicity testing and
other screening assays are discussed later in this chapter. Not surprisingly, the need for characterization
and detection methods is apparent in the four primary cross-cutting research categories identified in the
committee's first report: adaptive research and knowledge for accelerating research progress and
providing rapid feedback, quantifying and characterizing the origins of nanomaterial releases, processes
affecting hazard and exposure, and nanomaterial interactions in complex systems. Progress in the
development and validation of the methods and instrumentation needed for those categories ranged from
green to red. That range reflects the different characterization needs and scenarios identified. For
example, methods and instrumentation needed to characterize newly manufactured ENMs and their
important properties (with a few notable exceptions discussed below) in a well-characterized and
relatively simple medium (such as deionized water or simple physiologic buffer) are well established. The
variations in ENM properties (such as size) measured with different techniques are recognized and can be
documented with appropriate methods and metadata. Therefore, progress toward development of methods
and instrumentation in well-controlled, simple media is designated green.
However, there are fewer reliable methods for characterizing ENMs in increasingly complex and
less well-characterized media (such as blood and natural waters) because complex nonequilibrium
interactions between the ENMs and the components of the medium can lead to measurement artifacts or
even preclude measurement. For example, measuring the size of ENMs in fluid with light-scattering
methods and identifying a specific material with electron microscopy are difficult in the presence of other
background particles. Some research has been initiated to modify existing techniques (for example, x-ray
absorption spectroscopy [Lombi et al. 2012]) or to develop new ones (for example, hyperspectral imaging
[Badireddy et al. 2012] and single-particle ICP-MS [Mitrano et al. 2012]) to address the shortcomings.
Thus, the committee designated progress in developing methods and instrumentation as yellow in
“quantifying and characterizing nanomaterial releases” (NRC 2012, p. 181) and “processes affecting both