Environmental Engineering Reference
In-Depth Information
from a measurement point of view are described in ISO Guides 34 and 35. The
procedures for developing reference substances for toxicological testing are
described in the OECD GD34 (OECD, 2005).
6.3
Analytical Test Strategy in NP Exposure Assessment
The following three-tier analytical test strategy refl ects the authors view but is in
line with initial discussions at international standardization organizations, such
as the OECD working party on manufactured nanomaterials and the ISO
Nanotechnologies Technical Committee 229 (ISO/IEC/NIST/OECD, 2008).
6.3.1
Initial Material Characterization
Nanomaterials for risk assessment are best characterized in a tiered approach
where fi rst the material as produced (as a powder or dispersion in the reagents) is
characterized for its material properties and dynamic properties as supplied. The
list of important physicochemical properties provided by both OECD' s Working
Party on Manufactured Nanomaterials (2008) and the ISO Technical Committee
229 on Nanotechnology, WG3 Environment, Health and Security are almost identi-
cal to those in Figure 6.1, but there are a few exceptions; for example, the view of
the authors is that water solubility is a misleading term to use, since NPs are actu-
ally not dissolved in water but dispersed, and different chemical processes govern
solubility and dispersability. Also, representative TEM picture(s) are mentioned as
a property even though this is actually a method output that can be used to obtain
certain physico-chemical information but it is not in itself a property. The raison
d' être for this probably lies in the old saying 'a picture says more than a thousand
words'. However, see the discussion of representativeness in the microscopy section
(Section 6.2.6 ).
6.3.2
Fate and Behaviour Assessment
At the second characterization tier in environmental fate and behaviour studies
many of the physico-chemical properties mentioned above (or in Figure 6.1) are
relevant, but characterization needs to be performed under a range of relevant
environmental media conditions in order to generate process understanding and
parameters for deriving predictive models (Chapter 4). In addition, the OECD' s
Working Party on Manufactured Nanomaterials (2008) suggests the following list,
which is largely adopted from fate test strategies of conventional chemicals, and
still need to be scrutinized in the near future for relevance and applicability for
fate testing of nanomaterials:
• Dispersion stability in water
• Biotic degradability
• Ready biodegradability
• Simulation testing on ultimate degradation in surface water
• Soil simulation testing
• Sediment simulation testing
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