Getting to Green - Research Progress on Environmental Health and Safety Aspects of Engineered Nanomaterials - page 56

hazard and exposure” (p. 149). Progress in those research categories depends on the ability to measure
ENM properties in complex media and progress in the development of methods and instrumentation to
track, detect, and characterize ENMs in complex environments (such as soil or wastewater in which the
origins of ENMs and the composition of the solution are unknown and ENMs are present in very low
concentrations) has been particularly poor. New instrumentation for single-particle measurements has also
seen little progress, so this indicator was denoted red.
In summary, there has been progress in adapting existing tools for use in well-defined systems,
but considerably less progress has been achieved as the complexity of the medium has increased or in
understanding the properties of individual particles. The lack of adequate methods and instrumentation for
tracking, and for detection and characterization of ENMs in complex systems hinders research progress in
many critical research fields. The inability to isolate single-particles also constrains our ability to
determine mechanistically how ENM properties affect their behavior.
Steps to Improve Progress in Methods and Instrumentation Development
Advancing research requires methods and instrumentation for measuring key properties of ENMs,
particularly in complex media. There are several critical needs. First, the average properties of the ENMs
in relevant complex biologic and environmental media and in the matrices in which they will be used
need to be quantified and characterized. Second, the properties of single particles need to be measured so
that specific ENM properties can be associated with observed behavior and effects. Third, there needs to
be an ability to track ENMs in complex media and organisms (for example, using isotopic signatures or
radio-labeled materials). Fourth, methods to extract ENMs from complex matrices or to perform in-situ
measurements are needed. Finally, the methods developed need to be sensitive enough to be operable at
the very low concentrations of ENMs expected in the biologic and environmental samples.
There are two principal challenges in quantifying and characterizing the average properties of
ENMs in complex biologic and environmental matrices: the low concentrations of the ENMs in the
matrices and the unknown history of the ENMs before analysis. That is important because ENMs in
samples taken from organisms or the environment may undergo transformations that change their
properties and make it difficult to quantify and laborious to characterize them with existing methods.
Released materials in their environments cannot be characterized without appropriate measurement and
characterization methods. Appropriate methods to isolate nanoparticles from complex matrices (such as
field-flow fractionation or liquid extractions) and appropriate detectors for measuring chemical
composition, speciation, and other relevant properties (such as charge) need to be developed.
Spectroscopic methods, such as x-ray absorption spectroscopy and near infared fluorescence
spectroscopy, that eliminate the need to isolate ENMs from complex matrices (such as soil and tissue),
also need additional development. Spectroscopic methods require greater spatial resolution and sensitivity
to characterize and quantify ENMs at low environmental and in vivo concentrations. The ability to
monitor the transformations of ENMs directly in a matrix in real time would improve our understanding
of the critical processes that affect ENM behavior. That will probably require instrumentation that has not
been and is not being developed.
Single-particle characterization techniques are needed to determine how specific ENM properties
affect their behavior. Most ENMs are polydisperse and have varied properties, such as size, crystal
defects, and chemical composition. Exposure to ENMs is typically to a distribution of ENMs with known
average properties. Single-particle characterization methods would allow one to isolate how the specific
features of an ENM affect its behavior. Such methods as tethering ENMs to a transmission electronic
microscopy grid can enable tracking behavior of individual particles. Better spatial resolution of
microscopy and spectroscopy methods will also allow characterization of individual ENMs.
A critical research need that cuts across exposure and effects research is the characterization of
the properties of adsorbed macromolecules on ENMs, including the structure of the macromolecule and
the outer surface layers of the ENMs. That information is needed to describe properties and changes of