Environmental Engineering Reference
In-Depth Information
spray-on sunscreen. Based on information obtained about the quantity of nanoma-
terials present in the sunscreen, the suppliers' instructions regarding usage of
the product and making an estimate of the fugitive spray emission being 10%
of the total spray (indicating that 90% of the material actually deposits on the
surface of the skin), they estimated that an exposure concentration of 3.5 mg/m 3
was plausible. In an occupational context this would be a non-trivial exposure
concentration, albeit that the duration of exposure to this concentration will be
very short.
In an earlier part of their report they also estimated approximately 3 g might
be applied daily, which would give a skin coverage of about 1 mg/cm 2 of skin.
Of this, approximately 5% is the nanoparticle ingredient. Although very few mate-
rials have an occupational dermal exposure limit, this again would be a non-trivial
exposure.
These two examples illustrate that apparently non-trivial inhalation and dermal
exposure situations can occur in the use of relatively common place products which
can now contain nanomaterials. Exposure by ingestion can also occur in case of
food supplements and additives and non-intentional exposure by ingestion may
arise from food packaging products (Chaudhry et al. , 2008). At the current time no
coherent attempt has been made to derive estimates of consumer exposure for
nanoparticle-containing products. However, the above examples give suffi cient
cause to suggest that this is now overdue.
8.3.1.3
Environmental Exposure Scenarios
It is clearly conceivable that fugitive emission from processes in which nanomateri-
als are produced could potentially lead to increased air concentration of these
nanomaterials. As well as environmental exposure in these circumstances, it is
plausible that the general public would become exposed. It is likely that such emis-
sions would result in plume type dispersion.
One interesting application that could lead to the increased exposure of the
general population is the use of nanomaterials as a fuel additive. It has been widely
reported that cerium oxide has been used as an additive in diesel fuel and that this
has been used in a number cities in the UK.
Boxall et al. (2007) have estimated potential concentrations of cerium oxide in
air, based on assumptions of about the quantity of cerium oxide present in fuel, the
uptake of fuel containing cerium oxide and using dispersion models developed and
validated and used by the UK Highways Agency. In their assessment, using a mix
of traffi c type with traffi c fl ow at 40 km/h and at 1000 vehicles per day, they esti-
mated a cerium oxide concentration at a distance of fi ve metres from the road of
0.6
g/m −3 . In relation to occupational exposure this is very low. Their estimate,
however, did not take into account standing traffi c in congested city centre streets.
In these circumstances, it is likely that concentrations would be perhaps several
orders of magnitude higher that that reported. Clearly, however, the potential for
exposure scenarios of this type to result in signifi cant exposures needs to be further
evaluated.
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