Civil Engineering Reference
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stimulus in the organism in question, toxic effects of MNMs can differ
between species. For comprehensive MNM toxicity testing, it is thus neces-
sary to consider the analysis of multiple species such as, e.g., human, fi sh,
bacteria, algae, etc.
The biggest challenge for the evaluation of nanomaterial toxicity and
hazard is the sheer number of different materials - we can expect in excess
of 100,000 MNM enabled products in the next decade (Service, 2008). A
solution to the bottleneck in MNM testing is high throughput screening
(HTS). HTS became the leading paradigm in drug discovery in the late
1980s and early 1990s and generated many more lead compounds (Pereira
and Williams, 2007) than the labor-intensive 40-50-year-old descriptive toxi-
cology platforms used up to this point could handle. The toxicology depart-
ments had to adopt HTS methodologies (Dimasi, 2001) to keep up with the
number of chemical candidates that came out of HTS campaigns. The
resulting arsenal of HTS toxicology assays and platforms is large and much
of it can be transferred to ENM toxicity screening. It is interesting to note
that the National Academy of Sciences (NAS) has recognized the need for
novel methodologies which can support carrying out a large number of
toxicological tests without relying primarily on animal testing and put forth
a vision and strategy paper in which HTS methodologies are prominently
featured as one feasible approach for turning the vision into reality (Gibb,
2008). Similarly, the European Union has enacted the REACH program
under which all chemicals have to undergo toxicology testing and takes
notes from the EPA ToxCast program in which HTS toxicology methods
are applied towards screening chemicals for their toxicological properties
according to the NAS vision paper (Judson et al. , 2010).
7.4.1 Characterization of MNMs before toxicity screening
Before the actual toxicity testing, a thorough characterization of the MNMs
in 'dry' and 'as dispersed' form is necessary (see Table 7.3 for an overview
of MNM properties and frequently used techniques): while MNMs are typi-
cally delivered as a dry powder, when they come into contact with a living
entity and exert their toxicity, they will be in aqueous phase - be this now
in, e.g., a waste water matrix, or the lung fl uid of a mammal. While the 'dry'
characterization typically includes assessment of important metrics such as
size and shape as well as phase and crystallinity, one has to bear in mind
that MNMs can change quite drastically in aqueous phase: aggregation,
changes in surface charge, absorption of, e.g., proteins present in the aqueous
phase are quite common and infl uence the nano-toxicity. Hence, it is impor-
tant to determine not only the properties of an MNM 'as produced' in dry
powder form but also, e.g., the size, size distribution, state of dispersal/
aggregation, stability and the zeta-potential of the MNM in aqueous phase,
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