Field and Laboratory Measurements Related to Occupational and Consumer Exposures - Safety of Nanomaterials along Their Lifecycle - page 296

and cleaners). Most of the nanosprays contain nanosized metals or metal oxides.
In general, it can be concluded that the release method, for example, pressure and
nozzle size, determines the initial size distribution. For example, gas pressured spray
cans generate large fractions of aerosols with particle sizes below 100 nm. However,
the solute concentration will also significantly influence the number concentrations
of the released aerosols. There is no indication that the presence of NOAA in spray
solution affects the size distribution (Nørgaard et al. 2009; Nazarenko et al. 2011).
Most studies report that individual ENPs have been observed in the breathing zone
and could be deposited in the alveolar region of the lungs.
No evidence for exposure to NOAAs has been given by the few (field) stud-
ies on occupational spray coating of nano-enabled products in outdoor conditions
(Table 13.3), e.g. (van Broekhuizen et al. 2011; Dylla and Hassan 2012); however,
decisive conclusions cannot be drawn from the limited number of studies.
High energy dispersion of powders (Yang et al. 2011) will result in relatively high
concentrations of agglomerates in the breathing zone; however, the presence of pri-
mary particles has been shown as well. The latter will be much depending on the sta-
bility of the agglomerates of the powder and the shear forces applied to the powder
(Stahlmecke et al. 2009). A relatively low energy dispersion process, that is, manual
brushing, has been investigated for personal care consumer products (Nazarenko
et al. 2012). In this study mostly agglomerates were observed.
Most of the studies conducted for spray-can use were experimental studies in
small size experimental rooms (often glove boxes). Only a few studies characterized
the particle size distribution over a large size range (up to 10,000 nm). Chen et al.
(2010) reported a CMD of 75 nm (2.3) and a NMD of 395 nm (1.6) and MMAD of
836 nm (1.6). Other studies reported size modes below and above 100 nm. Quadros
and Marr (2011) reported NMD of 167 nm (±9) and 217 nm (±23). Bekker et al.
(2013) reported for various spray cans size modes ( D mob ) of 50 and 90 nm, and
modes between 140-210 D AED (electrical low pressure impactor data) and 500-600
nm (aerodynamic particle sizer data), which were similar to background. Delmaar
(2013, personal communication) found number mean diameters between 90-112 nm
and 160 nm for various spray cans, with MMAD ( D AED ) between 2.07 µm (±0.34)
and 4.2 µm (±0.41).
Nazarenko et al. (2012) studied the brush application of nano cosmetic powders
and reported size modes <100 nm and MMADs of 1.44 µm (GSD 1.7) to 1.65 µm
(GSD 1.7), whereas the regular powders showed a higher MMAD, that is, 2.86 (1.9)
µm to 3.12 (1.6) µm.
For high speed milling of powders simulating workplace exposure, Yang et al.
(2011) reported size modes of 37-525 nm ( D mob ).
13.3.4 s ourCe d omain 4: n anoPartiCle -e naBled e nd P roduCts
It is assumed that the liberation of NOAA from a matrix, for example, nanocom-
posites, and eventual discharge into the air (emission) will often result from a com-
bination of energy input, for example, by mechanical or thermal processes. These
processes and the composite material properties will determine the type of particles
being released as discussed in the chapter by Kuhlbusch and Kaminski (Chapter 16).