Risk Assessment of Manufactured Nanomaterials - Environmental and Human Health Impacts of Nanotechnology - page 402

dose-response relationships for a robust risk assessment of nanomaterials. The
representative nanomaterials chosen for case studies include single- and multi-
walled carbon nanotubes, silver nanoparticles, cerium oxide nanoparticles, tita-
nium dioxide nanoparticles, iron nanoparticles and carbon black. This work is
ongoing; however, industrial bodies such as the DuPont/Environmental Defense
Nano Risk Framework have considered risk assessment of individual nanomateri-
als using a life cycle approach (accessed at http://nanoriskframework.org/page.
cfm?tagID=1326), which suggests that a specifi c base data set is collected with the
need for further information identifi ed by defi ned criteria (Table 10.4). The ' trig-
gers' that require further information to be gathered include high exposure poten-
tial, high production volume, magnitude of environmental release, high potential
for chronic human/environmental exposure by repeated or continuous release,
uncertain or high inherent hazard potential and an incomplete base set of either
hazard or exposure data.
To date, the Nano Risk Framework has been applied to determine the risks
related to specifi c forms of titanium dioxide nanoparticles and zero-valent iron
nanoparticles (nZVI) by defi ning the substance and application, the lifecycles
(properties, hazards and exposure), evaluating the risks, assessing options, recording
the decisions and actions, and continuously reviewing and adapting with new infor-
mation. Titanium dioxide (TiO 2 ), found in paints, plastics and cosmetics is produced
in large amounts (e.g. over one million tonnes per annum) with a median particle
size between 250 and 350 nm (Gogotsi, 2006). The Nano Risk Framework has
assessed TiO 2 used as inorganic light stabilisers for polymers (particle size range
130-140 nm, with approximately 20% of particles with particles sizes less than
100 nm), which is found in a wide range of products including sporting goods,
outdoor furniture, fabrics and toys. Toxicological studies suggested that there was
no signifi cant variation between the effects of light stabilising TiO 2 and pigmenta-
tion TiO 2 , and an acceptable exposure limit (AEL) was set by DuPont (manufac-
turer) as 2 mg m − 3 . No discernible risks were associated with TiO 2 exposure here
( http://www.environmentaldefense.org/documents/6552_TiO2_Summary.pdf ),
although other studies have shown hazard or potential hazard from TiO 2 nanoma-
terials. The nZVI assessment (primary particle size of 100 nm), used as a reagent

to destroy organic contaminants in ground water, suggested that whilst many manu-
facturers provided some hazard data this may not have been specifi c to nZVI and
the extent of environmental and human exposure must be taken into consideration
as well as the ultimate fate of nZVI. The Nano Risk Framework also considered
carbon nanotubes which are not discussed here.

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10.6 Data Gaps in Risk Assessment of Nanomaterials

The knowledge gaps in nanomaterial risk assessment are signifi cant at this early
stage in the science. The issue of problem formulation is hindered by a lack of data
on exposure and biological effects (Handy et al. , 2008a), and the current focus is
on test organisms used in the regulatory arena, rather than the diverse range of
organisms in the natural environment. So while data are being collected on fi sh
species and Daphnia magna , there are few data on many other organisms; especially