Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 316

perhaps by incineration or some other process such as shredding or grinding, should
be considered. Again in these circumstances the potential for exposure to those
carrying out these procedures does exist. Hence, it may be easily seen that for a
single material there are multiple exposure scenarios, which may or may not occur
depending on the details of manufacture, use and disposal of that material.
Throughout these scenarios the population exposed, the levels of exposure, the
duration of exposure and the nature of the material to which people are exposed
are all different.
Consumers may therefore become exposed as a result of nanomaterial contami-
nation in air, water or the food chain, or through the use of consumer products
containing nanomaterials.
Discharge of materials into the environment is feasible as waste or industrial
pollution, directly into the air or water systems or due to deliberate release in
applications such as remediation of contaminated land.
In assessing human exposure in all of these scenarios it is necessary to consider
the route of entry into the human body. In occupational exposure most emphasis
has (rightly) been placed on exposure by inhalation. More recently, however,
emphasis has been put on dermal exposure and exposure by ingestion. For
nanomaterials, given their mobility and potential for translocation, it is highly
appropriate to consider these other routes. In this section potential occupa-
tional, environmental and consumer exposure scenarios are examined in more
detail.

8.3.1.1 Exposures in Occupational Scenarios

In all nanoparticle production processes there is a potential for exposure to occur
at both the synthesis and recovery phase of the process (Aitken et al. , 2004 ). The
nature of the exposure, the likely level and the probability of exposure will differ
according to the specifi c process and the stage of the process. Similarly, the optimum
strategy to control exposure, and the effi cacy of the control methods used, will differ
depending on the specifi c process.
In gas phase processes, nanoparticles are formed as an aerosol inside a reactor
vessel. Hence, there are potential risks of inhalation exposure in the event of
leakage of product from the vessel, particularly if the system operates at positive
pressure. The nature of the aerosol released would be dependent on the point in
the process at which leakage occurs. In the initial stages of the process, primary
nanoparticles could be released. Later in the synthesis process a more aggregated
aerosol (still of nanoparticles) could be released. Ultimately, particles in the form
of loosely bound agglomerates could be released into the workplace air. Exposure
by inhalation could also occur during product recovery. The recovery method will
differ depending on the process. In some gas phase processes, product nanoparticles
are collected in bag fi lters. These are reverse pulsed and the product nanoparticles
recollected into a hopper or other receptacle. Ineffective fi lter systems could result
in escape of product into the working environment, particularly where recirculation
into the workplace air occurs. During the recovery stage and in any further process-
ing or packing the particles are likely to be in the form of an agglomerated bulk