Biomedical Engineering Reference
In-Depth Information
so that a reliable understanding of exposures can be built. CNT-polymers were
chosen as a case study for method requirements in the NanoRelease project. The
approaches chosen in these projects give insight into the relative likelihood of human
health risk for nanoscale particles by an “understand exposure first” approach to the
risk management that is necessitated by the tremendous variation in possible nano-
material characteristics. Toxicity studies of the “released” nanomaterials are needed
to allow full assessment of the potential risk; however, in the absence of those stud-
ies, we are forced to rely on studies of “pristine” materials, but only after we have a
better understanding of the materials to which actual exposures occur.
18.2 RELEASE OF CNTs DURING THE LIFECYCLE
As discussed by the NanoRelease Project Steering Committee (NanoRelease
Consumer Products 2014) and reviewed by Nowack et al. (2013), it is important to
segregate the question of “Are uses of a nanomaterial safe?” into materials, uses, and
stages of the life of the material (lifecycle) so that statements of risk can be properly
focused on particular populations and possible risk management points. In so doing,
it is clear that the potential for release of CNTs will vary from essentially zero for
parts of the lifecycle in which contact does not occur with potential exposure media,
to measureable levels under conditions in which disaggregation of the matrix holding
the CNT may occur. The releases will depend on the material, use, and environmen-
tal conditions for the particular points in the lifecycle. Nowack et al. (2013) illustrate
this point and identify release and exposure points of greatest interest across antici-
pated uses for CNTs in a polymer matrix. No specific lifecycle descriptions for con-
ductive plastics have been published to our knowledge so the approach provides an
approximation that aids in bounding discussion of likelihoods of release and expo-
sure. Nowack et al. considered scenarios with respect to the following:
• Mechanisms of release (e.g., abrasion, weathering by ultra violet (UV)
radiation or water)
•
Form of the release (e.g., free CNTs or CNT embedded in particles)
•
Magnitude of release
•
Estimates of frequency/duration of release
•
Properties of the composite affecting release (e.g., UV stabilizers or
polymer type)
•
Site of release (e.g., to air following abrasion/cutting in a manufacturing
facility, dermal/air exposure for general population/consumer, workplace
exposures to release from products, and air/water for environmental and
workplace exposures during disposal)
•
Environmental conditions affecting release (e.g., UV intensity, humidity, or
abrasion conditions)
•
Populations potentially exposed (e.g., for manufacturing: workers; for
product life/usage: workers, the general public [if the product is in a public
building/space], or specific consumers [who buy the product])
The general structure of the stages considered is represented in Figure 18.1.
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