Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 338

immediately formed highly branched aggregate structures. During the process of
collection, these ' aggregates ' agglomerated further in cyclones and bag houses
to much larger entities. Carbon black was packed for shipment either as pellets or
as 'fl uffy' agglomerates. Measurements were conducted for PM 10 mass concentra-
tions and for sub-micrometre number size distributions simultaneously within the
work areas and outside at the comparison site. Ratios were developed for the
simultaneous measurements. Particle size distributions were measured with a
SMPS (Platform 3080 series; Differential Mobility Analyzer 3081; Condensation
Particle Counter 3025; and model 3077 Aerosol Neutralizer; TSI Inc., Shoreview,
Minn.), which determined the particle number size distributions in the size range
15-734 nm. An aerodynamic particle sizer (APS, model 3310; TSI Inc.) was used
to measure particle size distributions in the range 0.5- 15 µ m (dae, aerodynamic

diameter).
Results were expressed in terms of levels of ultrafi ne particle number concentra-
tions (UFP, 100 nm). No elevated ultrafi ne particle number concentrations with

respect to ambient were determined in the work areas of Plant 1, intermittently
elevated concentrations at Plant 2, and permanently elevated concentrations at
Plant 3. The intermittently elevated UFP concentrations in the pelletiser and reactor
areas of Plant 2 were considered to be related to nearby traffi c emissions. Both
work areas of Plant 3 showed elevated UFP concentrations in the pelletiser and
reactor areas. In the case of the reactor, which was the only enclosed reactor area
investigated among the three facilities, the source of the elevated UFP number
concentration was considered by the authors to be most likely attributable to grease
and oil fumes from maintenance activities, a conclusion supported by carbon frac-
tionation analysis. The elevated UFP number concentrations in the pelletting area
in this same plant were identifi ed by the authors as resulting from leaks in the
production line, which allowed particulate matter to escape into the work area. The
cause of the high number concentrations and the high mass concentrations was due
to emissions stemming from one or more leaks in the production line, specifi cally,
seals on dryers immediate adjacent to the pelletting area, as observed by one of
the authors.
At the peak size, at 90 nm, the ratio of counts in the pelletting area to the com-
parison site was 1800, a very signifi cant increase. While the authors rightly state
that 'no carbon black is released in the reactor and pelletting areas from the closed
production lines under normal operating conditions', it is interesting that this sig-
nifi cant leakage had not been detected in the plant, prior to this measurement
programme.
Aitken et al. (2004) reviewed data from 'existing nanoparticle processes' . This
study included data from established industries where materials in the nanoparticle
size range have been manufactured for a number of years, such as carbon black
and TiO 2 , nanoparticle by-product processes such as welding and soldering and
relevant powder handling processes such as in the pharmaceutical industry. Their
data are summarised in Table 8.5.
A key issue here is discrimination of the manufactured nanoparticle from the
background aerosol. It is not clear whether ambient aerosol counts (e.g. from com-
bustion or traffi c) have been subtracted in the studies where number counts have

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