Biomedical Engineering Reference
In-Depth Information
airborne size will alter the deposition mechanisms for the engineered nanomaterial at the receptor
and hence the effective dose. (It is not understood whether the agglomeration process affects the
toxicological mechanisms as well.) Furthermore, growth and/or attachment of airborne-engineered
nanomaterials to other particles challenges the established methods for their adequate characteriza-
tion. Separation and identification of engineered nanomaterial against the submicron background
aerosol originating from different sources is therefore a difficult or impossible task facing engi-
neered nanomaterial monitoring and characterization in workplaces and other environments [72].
Currently, there are no rapid techniques available that would allow online distinction between
background NPs and engineered nanomaterial. Instead, one has to collect the aerosol and do off-
line imaging or compositional analysis, for example, by transmission electron microscope (TEM).
Therefore, TEM remains the gold standard for this type of analysis [72].
Novel materials introduce entirely new particle shapes, such as CNTs that, upon release into the
air, can form larger fiber-like structures resembling, for example, crocidolite fibers with potentially
serious health consequences [73]. The addition of fullerene structures to the backbone of SWCNTs
produces nanobuds that may be associated with unexpected biological effects [74]. The effects of
functionalization of engineered nanomaterials add to the complexity of their risk assessment and
are beyond this discussion, and for the most part, are undone so far.
The thorough characterization of airborne-engineered nanomaterial is thus complicated by the
dynamic behavior of the engineered nanomaterial as an aerosol as well as the structural complexity of
the individual particles. The large set of parameters required for their complete characterization, the
range of engineered nanomaterials already in use, and the multitude of biological responses create a
special challenge for this undertaking. Currently, there is no robust set of devices that could be used for
monitoring, measuring, and characterizing engineered nanoparticle (ENP) in workplace environments.
19.7.2 a
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Measurement and monitoring of engineered nanomaterial present in the air of workers' breath-
ing zones means capturing all relevant information about the amount (number, surface area, or
mass concentration) and size distribution, as well as shape, composition, and chemical reactivity of
airborne-engineered nanomaterial in a given size class or a broad size range. Selection of the most
relevant metric(s) for health-related sampling of the engineered nanomaterial is an important com-
ponent in the development of the concepts, methods, and technology for engineered nanomaterial
monitoring at workplaces [75]. For this purpose, understanding the relationship between engineered
nanomaterial metrics and toxicological effects of engineered nanomaterial is necessary, but as yet
it is unavailable. This is because a consensus on the correct metrics to be measured to assess the
exposure to engineered nanomaterial has not yet been reached internationally.
The multitude of relevant engineered nanomaterial metrics, in combination with the different
possible release mechanisms for engineered nanomaterial into workplace air as well as the poorly
defined transport pathways between the source and receptor (which all affect the particle character-
istics) make it imperative to establish and define the typical engineered nanomaterial exposure sce-
narios. For example, one should assess exposure to “fresh engineered nanomaterial” emitted from
different production processes as well as for settings in which prevalent exposure occurs to “aged”
and “attached” engineered nanomaterial [62]. These work processes may include, for example, han-
dling and packing of partly agglomerated and aggregated engineered nanomaterial. It is important
to obtain data from these types of exposure settings to be able to assess true exposure levels of
engineered nanomaterial in workplaces [72].
Currently, aerosol technology disposes off a range of methods for monitoring of the engineered
nanomaterial containing aerosols. These include online as well as off-line methods to capture a
number of different metrics. The array of techniques and concepts for obtaining physical aerosol
information related to concentration or size is relatively large, with a general trend away from mass
toward number- or surface area-based techniques [76]. Some devices are stationary and capable of
