Nanotechnology White Paper - US Environmental Protection Agency

32 EPA Nanotechnology White Paper
20 nm 20 nm
(A)
(B)
Figure 17. Transmission Electron Microscope (TEM) image of aerosol-generated TiO 2
nanoparticles.
(A) Un-aggregated and (2-5 nm) (B) and aggregated (80-120 nm), used in exposure studies to determine
the health impacts of manufactured nanoparticles. Nanoparticle aggregation may play an important role
in health and environmental impacts. (Images courtesy of Vicki Grassian, University of Iowa [Grassian,
et al., unpublished results])
A given nanomaterial can be produced in many cases by several different processes
yielding several derivatives of the same material. For example, single-walled carbon nanotubes
can be produced by several different processes that can generate products with different
physical-chemical properties (e.g., size, shape, composition) and potentially different ecological
and toxicological properties (Thomas and Sayre, 2005; Oberdörster et al., 2005a). It is not clear
whether existing physical-chemical property test methods are adequate for sufficiently
characterizing various nanomaterials in order to evaluate their hazard and exposure and assess
their risk. It is clear that chemical properties such as boiling point and vapor pressure are
insufficient. Alternative methods for measuring properties of nanomaterials may need to be
developed both quickly and cost effectively.
Because of the current state of development of chemical identification and
characterization, current chemical representation and nomenclature conventions may not be
adequate for some nanomaterials. Nomenclature conventions are important to eliminate
ambiguity when communicating differences between nanomaterials and bulk materials and in
reporting for regulatory purposes. EPA’s OPPT is participating in new and ongoing
workgroup/panel deliberations with the American National Standards Institute (ANSI), the
American Society for Testing and Materials (ASTM), and the International Organization for
Standardization (ISO) concerning the development of terminology and chemical nomenclature
for nanosized substances, and will also continue with its own nomenclature discussions with the
Chemical Abstracts Service (CAS).
3.3 Environmental Fate of Nanomaterials
As more products containing nanomaterials are developed, there is greater potential for
environmental exposure. Potential nanomaterial release sources include direct and/or indirect
releases to the environment from the manufacture and processing of nanomaterials, releases from