Risk Assessment of Manufactured Nanomaterials - Environmental and Human Health Impacts of Nanotechnology - page 401

to indicate which areas of evidence should be considered further. This is already
possible for some chemicals to a certain extent with QSAR. However, its suitability
for use with nanomaterials remains uncertain. If the size or shape of a nanomaterial
determines its toxicity, then the relationship may be clear and the outcome only
affected if the environment transforms the nanomaterial (either by physical or
biological methods). If there are other factors that contribute to the inherent toxic-
ity of the material, for example the surface chemistry, then the need for specifi c
information becomes clear (including information on the aerodynamic diameter,
route into body and potential for agglomeration).
Recommendations have been made on the base set of characterisation data
required for a good toxicological experiment (Handy et al. , 2008a, 2008b; Crane and
Handy, 2007; Crane et al. , 2008). However, not all the published studies on biological
effects provide this information at present. An agreement has not been reached on
standard methodology to measure exposure in the environment and, until such
agreement is reached, the quality of each measurement should be considered on the
basis of its scientifi c merit (e.g. use of calibrations, standard addition tests, spike
recovery tests, matrix effects and other controls to prove the methodology). Overall,
there is suffi cient peer reviewed laboratory data to show that, in principle, nanoma-
terials can have toxic effects (e.g. Handy et al. , 2008a). However, the lines of evidence
for environmental exposure are few, and currently this is derived by modelling infor-
mation on product usage and manufacture for environmental risk assessments
(Boxall et al. , 2007). The evidence base for workplace exposure is more robust, but
there remains a requirement to measure nanomaterials in workplace air to quantify
exposure concentrations, and correct this for the benefi t of any protective clothing
or other controls (e.g. use of dust masks or ventilation).
Risk analysts consider both positive and negative evidence to balance the weight
of evidence. At this early stage in the science it is imperative that scientifi c reports
of ' no effect ' or even ' benefi cial effects' are published, so that this information can
be balanced against some of the more high profi le reports on adverse effects.
Researchers should also consider, and look for, positive effects of nanomaterial
chemistry. For example, aggregation may limit the long range transport of nano-
materials in the environment in the short term. Some nanomaterials may chelate
or bind other organic chemicals to reduce their toxicity in mixtures. These ideas
need to be explored, and the data collected made available for the risk analysis.

10.5 International Case Studies

International bodies, including OECD, ECHA and EPA, recognise that engineered
nanomaterials are currently in use but that more information is required to conduct
a complete risk assessment of these materials (as discussed in reports including
RS/RAEng, 2004 and SCENIHR, 2005). Whilst fundamental research on the
toxicity and actions of manufactured nanomaterials is ongoing, risk assessment
case studies of existing nanomaterials are also being used to identify knowledge
gaps and prioritise further research; the OECD Working Party on Manufactured
Nanomaterials (accessed at http://www.oecd.org/department/0,3355,en_2649_
37015404_1_1_1_1_1,00.html) has identifi ed the need to consider the exposure and