Overview of Nanoscience in the Environment - Environmental and Human Health Impacts of Nanotechnology - page 20

transport and removal of silica, anatase and fullerene based nanoparticles in porous
media. They found that the removal of anatase is less signifi cant at higher fl ow rates.
However, no dependence on velocity of particle passage through the porous
medium was observed for silica particles and the fullerene based nanoparticles. This
was explained by the very small value of the collision effi ciency factor in the case
of silica and the deposition of fullerene based nanoparticles on the porous media
at higher fl ow rates after one void volume, which limits the interaction of these
nanoparticles with the porous media and reduces particles removal afterwards
(Lecoanet and Wiesner, 2004 ).
The discussion above, in addition to previous knowledge on colloidal transport
in porous media, suggests that the mobility of nanoparticles in soils depends on: (i)
nanoparticle physical-chemical characteristics, that is size, shape, surface coatings
and stability; (ii) the properties of the soil and environment, that is clay, sand,
colloids, natural organic matter, water chemistry and fl ow rates; and (iii) the inter-
action of nanoparticles with natural colloidal material, that is surface coating,
aggregation/disaggregation and sorption to larger particles. The more theoretical
aspects of particle movement in porous media are discussed in Chapter 4.

1.14 Potential for Human Exposure

For nanomaterials to cause concern to human heath it is necessary to be exposed
to them. There are multiple exposure scenarios depending on the details of manu-
facture, use and disposal. 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. In an occupational context, exposure to nano-
materials can occur for workers at all phases of material life cycle. During the
development of a new material, it is probable that material will be produced under
tightly controlled conditions, typically in very small quantities. Once the material
moves into commercial production, exposures can occur potentially during synthe-
sis of the material or in downstream activities such as recovery, packaging, transport
and storage. In these circumstances, the quantities of materials being handled will
typically be much larger. Nanomaterials may also be incorporated, for example,
into a composite material, which may be subsequently re-engineered or repro-
cessed by cutting, sawing, or fi nishing. Again in these circumstances the potential
for exposure exists. Finally, end of life scenarios can be considered, where the mate-
rial is disposed off, perhaps by incineration or some other process such as shredding
or grinding. Again in these circumstances the potential for exposure to those car-
rying out these procedures does exist. 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 lands.
Therefore, humans may become exposed as a result of nanomaterial contamination
in air, water or the food chain, or through the use of consumer products containing
nanomaterials.
In considering human exposure for all of these scenarios, it is necessary to
consider the route of entry into the human body. In occupational exposure most