Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 333

be worn by a worker, for example in a backpack, although depending on the nature
of the work, this is likely to be cumbersome. The location of these area monitoring
instruments would need to be considered carefully. Ideally, they should be placed
close to the work areas of the workers but other factors, such as size of the instru-
mentation, power source, an so on, will need to be considered.
As a fi nal stage, NIOSH recommends that personal sampling using fi lters or grids
suitable for analysis by electron microscopy or chemical identifi cation should be
employed, particularly if measuring exposures to specifi c nanoparticles is of inter-
est. Electron microscopy can be used to identify the particles and can provide an
estimate of the size distribution of the particle of interest. The use of a personal
cascade impactor or a respirable cyclone sampler with a fi lter, though limited, will
help to remove larger particles that may be of limited interest and allow a more
defi nitive determination of particle size. Standard analytical chemical methodolo-
gies should be employed to analyse the fi lters.
NIOSH (2008) states, 'By using a combination of these techniques, an assessment
of worker exposure to nanoparticles can be conducted. This approach will allow a
determination of the presence and identifi cation of nanoparticles and the charac-
terization of the important aerosol metrics. However, since this approach relies
primarily on static or area sampling some uncertainty will exist in estimating
worker exposures.' Clearly, even such a detailed assessment is limited and more
detailed schemes are required for research purposes, which might be streamlined
for routine monitoring.
8.3.4 Studies Investigating Nanoparticle Exposure
8.3.4.1 Exposures in New Nanoparticle Processes
Few studies have as yet directly investigated exposure in new nanoparticle pro-
cesses. The study by Maynard et al. (2004) is perhaps the single most thoroughly
described study available at this time. Maynard carried out a laboratory based study
to evaluate the physical nature of the aerosol formed from single-walled carbon
nanotubes (SWCNT) during mechanical agitation. This was complemented by a
fi eld study in the United States in which airborne and dermal exposure to SWCNT
was investigated while handling unrefi ned material. Details of the fi eld study are
provided below.
Two techniques for producing SWCNT were investigated. These were the laser
ablation and high pressure carbon monoxide (HiPCO) processes. Both of these
processes lead to the production of a very low density material comprised of
nanometre-diameter catalyst metal particles, CNTs and other forms of elemental
carbon which are manually recovered prior to further processing.
Measurements of unprocessed airborne nanotube exposures were made at four
plants where SWCNT material was removed from production vessels and handled
prior to processing. Instruments used included CPCs and SMPSs. Filter samples for
electron microscopy analysis were also collected. The fi lter samples were taken over
the time period the workers spent in the enclosure, which was typically about half
an hour.