  The development of science-based categorization strategies for regulatory
purposes is not a simple task. It requires understanding the needs and capacity
of a wide variety of stakeholders and should consider the potential risks and
unintended consequences. For an evolving science area, such as
nanotechnologies, the overall uncertainties of designing an effective
categorization scheme can be significant. Future nanomaterials may be far more
complex and may integrate far different functionalities than modern
nanomaterials. There is much that has been learned from our experience with
legacy nanomaterials and particulate substances in general. Most of the modern
nanomaterials are not new nor dramatically different from parent or existing
chemical substances, however there are some nuances. Applying these learnings
to define reasonable science-based categories that consider how different
emerging nanomaterials might be from existing known substances (while
integrating sound concepts as they develop) would be a pragmatic and flexible
path forward. However, there are many barriers down this road including a need
for improvement and updates to chemical classification systems to improve
hazard and risk communications, while promoting transparency and consistency.
