Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 247

exposure concentrations at various locations, for example, in work environments. This
approach is exemplarily discussed in Figure 12.1 (Schneider et al. 2011) but can be
used in principle for all release, transport, and transformation processes.
Necessary input information for the modeling of transport and transformation
processes of released nanomaterials includes particle number, surface area and/or
mass concentrations, size distributions, release rates, and detailed information on the
material and release process itself: Is the nano-object still embedded in the matrix,
released as an agglomerate or a primary nanoscaled particle? Further information
on the matrix material itself is also needed to enable the assessment of possible
degradation of the matrix material, which ultimately would lead to the release of an
embedded persistent nano-object.
The actual release characteristics and hence model input data are dependent on the
release process itself. This means that, for example, nano-SiO 2 particles that were dis-
persed in a polyamide (PA) composite matrix will be released in a different form into
the air during sanding compared to incineration. While the primary nanoparticles will
most likely be embedded in the matrix when released during sanding, all carbon may
be combusted and pure nano-SiO 2 released by incineration. But, also different input
data may be needed for one single release process. Taking sanding of a nanocomposite
surface with different sanding papers performed by different people as an example,
possibly significant variations can be observed: coarse paper, fast and heavy weight
compared to fine paper, and relatively slow and low weight sanding (Figure 12.2).

Size
distribution

Source

Size
distribution

Source

LCIR

Personal enclosure

Deposition if
electrical field

Coagulation
scavenging

LCIR

FF-surfaces

NF-surfaces Far-field

Deposition
if < 100 nm
or > 1 µm

Near-field

Coagulation
scavenging

Personal enclosure

Receptor

RPE

Size fractions
number of primaries
governing state of agglomeration
active surface area

Size fractions
number of primaries
governing state of agglomeration
active surface area

Receptor

RPE

(a) (b)

FIGURE 12.1 Conceptual model for inhalation exposure: (a) near-field (NF) source and
(b) far-field (FF) source. The rectangles indicate the compartments, whereas the callouts indi-
cate the transport process. LCIR, local influence region; RPE, respiratory protective device.
(Adapted by permission from Macmillan Publishers Ltd., J. Expos. Sci. Environ. Epidemiol .,
Schneider, T. et al., Conceptual model for assessment of inhalation exposure to manufactured
nanoparticles, 21(5); 450-463, copyright 2011.)