Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 317

powder. The likelihood of exposure by inhalation will be dependent on the details
of the process and the characteristics of the product.
In gas phase processes, there are potential risks of dermal (and ingestion) expo-
sure by touching surfaces contaminated by airborne releases, handling of product
during recovery and processing or packing and during maintenance or cleaning of
the plant and workplace.
In vapour phase processes, for example CVD, nanoparticle formation is on a
substrate, so direct release of particles during synthesis into the workplace air is
unlikely. Product recovery is likely to involve mechanical removal of particles from
deposition substrates. This could be manual or automated. Depending on the level
of energy used, this could result in re-suspension of product into the air. While it
unlikely that this would be in the form of discrete nanoparticles, agglomerations of
nanoparticles, possibly in the respirable size range and so able to enter the respira-
tory system, may be produced. Any post-recovery processing and packing is likely
to be similar to gas phase processing, with similar risks of exposure. Scenarios for
dermal and ingestion exposure will be similar to gas phase processes.
In colloidal and other chemical processes particle formation is in liquid suspen-
sion, so direct exposure by inhalation is unlikely during the synthesis stage. In some
of these processes, product recovery is by spray drying in which the product is
sprayed into an evaporation chamber. In these situations, airborne exposure is pos-
sible in the event of leakage, although it is unlikely to be to primary single nanopar-
ticles but rather to be agglomerates of nanoparticles. Spillage of liquid product in
the workplace, followed by evaporation and cleaning, could result in airborne dis-
persion and inhalation exposure. Again, this is more likely to be to agglomerated
materials.
In these processes, dermal (and ingestion) exposure could occur as a result of
spillage in the workplace. Exposure could be due directly to the suspension or to
dried material. Handling of the product during recovery/packing and maintenance
and cleaning could also result in dermal exposure.
Once potential applications of nanomaterials begin to be considered, the number
of exposure scenarios and the likely differences in nature, intensity and level of
exposure increase dramatically. In a general sense, use of nanomaterials as a feed-
stock in producing further materials would result in exposure scenarios typical of
powder handling activities. These scenarios would include activities such as bag
opening, powder transfer, mixing and so on. Exposures in these scenarios would
depend very much on the dustiness of the material, the quantities involved, and the
type of control systems in place.
It is unlikely that the energy involved in these processes would be suffi cient
for signifi cant concentrations of single nanoparticles to be released from agglomer-
ated powders (at least on a mass basis). Nevertheless, all of these types of activities
give the possibility for respirable dust to be released into the air, which in these
circumstances may contain strongly or loosely bound agglomerations of
nanoparticles.
When nanomaterials become part of a downstream product or formulation, the
types of exposure scenarios are then highly dependent on the purpose and use of
that product. These may be dramatically different dependent on the product type