Classification Strategies for Regulatory Nanodefinitions - Safety of Nanomaterials along Their Lifecycle - page 45

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Classification Strategies
for Regulatory
Nanodefinitions

Wendel Wohlleben and Philipp Müller

CONTENTS
3.1 Definitions of Nanomaterials for Regulatory Purposes ................................. 47
3.2 Methods to Measure the Size Distribution in Number Metrics:
For Powders ................................................................................................ 49
3.3 Methods to Measure the Size Distribution in Number Metrics:
For Suspensions .............................................................................................. 52
3.4 Sample Preparation for Fractionating and Counting Techniques ................... 54
3.5 Tiered Testing for Cost-Effective Screening and Confirmation ..................... 55
3.6 Conclusion ...................................................................................................... 56
References ................................................................................................................ 57

3.1 DEFINITIONS OF NANOMATERIALS
FOR REGULATORY PURPOSES
What is a nanomaterial? Focusing on materials science, only materials with size-
specific performance would be considered as nanomaterials; in a strict sense, one
may even require that these properties do not simply scale with size, but that they
exhibit a threshold behavior. Consider QDots as positive examples (luminescence
vanishes for particles larger than a few nm), and ultraviolet (UV)-absorbing pig-
ments as negative examples (UV absorption is less effective with increasing size,
but does not vanish). Focusing on innovation processes, the intention at the time of
production may be another criterion. On the contrary, the ISO terminology (ISO/
TS 27687:2008, nanoparticle, nanofiber, and nanoplate) focuses on geometrical
structures with the criterion that any external dimension of the material is in the
nanoscale or the material having internal structure in the nanoscale.
The practical value of a nanodefinition for regulatory purposes is a filtered mar-
ket screening that identifies materials that may require special attention and adapted
methods to assess hazard, exposure, and risk—such as the methods presented in this
topic. Regulators around the world have combined several elements: size ranges,
cut-offs, intention, size-specific properties, and/or properties that guide the hazard-
assessment such as solubility (Table 3.1). The European Cosmetics Directive, the

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