Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 334

The sample scenarios were as follows:

• Laser ablation facility: sampling carried out during material removal and clean
up.
• HiPCO process removal simulation: removal of SWCNT was simulated by
pouring previously generated material between two buckets normally used for
collecting nanotubes. Sampling occurred during fi lling, pouring and clean up
activities.
• Laser ablation process removal simulation: due to space constraints the collec-
tion chamber for the laser process was removed from the production system and
placed into the clean air enclosure for powder removal.
• HiPCO process: Collection chamber was removed from the production system
and placed into the clean air enclosure for powder removal.

The samples were analysed for iron and nickel as surrogates for total nanotube
product mass, thus providing a low limit of detection while discriminating between
SWCNT and other airborne material. SWCNT mass was estimated for each sample
assuming a combination of nickel and iron particles constituted 30% of the mass
of the material.
Estimates of nanotube concentrations ranged from 0.7 g/m 3 in the ablation facil- µ

g/m 3 in the HiPCO process. SEM analysis of fi lter samples indicated that
many of the particles appeared compact, rather than having an open, low density
structure more generally associated with unprocessed SWCNT. Some open struc-
tures were observed, including some large (non-respirable) clumps.
Estimates of the SWCNT material on the individual gloves ranged from 217 to
6020

ity to 53 µ

g, with most of the material appearing on the parts of the gloves in direct
contact with surfaces (inner surfaces of fi ngers and palms). Although the use of
gloves and personal protective equipment (PPE) will minimise dermal exposure
during handling of this material, the possibility for large clumps to become airborne
and remain so for long periods may lead to dermal exposures in less well protected
regions. Measurements indicated higher air and glove SWCNT concentrations for
HiPCO material. These higher levels may have been associated with the lower
density, 'fl uffi er' HiPCO material becoming more easily airborne as large clumps
of material.
Inspection of samples showed relatively few particles. Samples from HiPCO
SWCNT contained a small number of particles, in the order of 100

µ

m to 1 mm in
diameter, with relatively open ' nanorope ' structures. However, most micrometre-
sized particles in the analysed HiPCO sample appeared to have a compact struc-
ture, with very few nanotubes apparent. In contrast, micrometre-sized particles
from the laser ablation process were more clearly comprised of nanoropes. No
evidence of millimetre-sized nanotube material clumps were found in aerosol
samples from laser ablated material.
While laboratory studies have indicated that with suffi cient agitation SWCNT
material can release fi ne particles into the air, the aerosol concentrations generated
while handling unrefi ned material in the fi eld at the workloads and rates observed
were low in mass terms. In none of the fi eld studies is there any indication
that handling the nanotube material leads to an increase in the number concentra-

µ