Nanotechnology White Paper - US Environmental Protection Agency

EPA Nanotechnology White Paper
polychlorinated hydrocarbons, TNT, dyes, and inorganic anions such as nitrate, perchlorate,
dichromate, and arsenate. Further investigations are underway with bimetallic nanoparticles
(iron nanoparticles with Pt, Pd, Ag, Ni, Co, or Cu deposits) and metals deposited on nanoscale
support materials such as nanoscale carbon platelets and nanoscale polyacrylic acid (Zhang,
2003). Nanosized clusters of C60 have been shown to generate reactive oxygen species in water
under UV and polychromatic light. Similar colloids have been reported to degrade organic
contaminants and act as bacteriocides (Boyd et al., 2005). Fullerol (C60(OH)24) has also been
demonstrated to produce reactive oxygen species under similar conditions (Pickering and
Wiesner, 2005).
3.3.8 Applicability of Current Environmental Fate and Transport Models to Nanomaterials
When performing exposure assessments on materials for which there are no experimental
data, models are often used to generate estimated data, which can provide a basis for making
regulatory decisions. It would be advantageous if such models could be applied to provide
estimated properties for nanomaterials, since there is very little experimental data available for
these materials. The models used by EPA’s Office of Pollution Prevention and Toxics (OPPT)
to assess environmental fate and exposure, are, for the most part, designed to provide estimates
for organic molecules with defined and discrete structures. These models are not designed for
use on inorganic materials; therefore, they cannot be applied to inorganic nanomaterials. Many
models derive their estimates from structural information and require that a precise structure of
the material of interest be provided. Since many of the nanomaterials in current use, such as
quantum dots, ceramics and metals, are solids without discrete molecular structures, it is not
possible to provide the precise chemical structures that these models need. While it is usually
possible to determine distinct structures for fullerenes, the models cannot accept the complex
fused-ring structures of the fullerenes. Also, the training sets of chemicals with which the
quantitative structure-activity relationships (QSAR) in the models were developed do not include
fullerene-type materials. Fullerenes are unique materials with unusual properties, and they
cannot be reliably modeled by QSARs developed for other substantially different types of
materials.
In general, models used to assess the environmental fate and exposure to chemicals are
not applicable to intentionally produced nanomaterials. Depending on the relevance of the
chemical property or transformation process, new models may have to be developed to provide
estimations for these materials; however, models cannot be developed without the experimental
data needed to design and validate them. Before the environmental fate, transport and
multimedia partitioning of nanomaterials can be effectively modeled, reliable experimental data
must be acquired for a variety of intentionally produced nanomaterials.
However, models are also used which focus on the fate and distribution of particulate
matter (air models) and/or colloidal materials (soil, water, landfill leachates, ground water),
rather than discrete organics. For example, fate of atmospheric particulate matter (e.g., PM10)
has been the subject of substantial research interest and is a principal regulatory focus of EPA=s
Office of Air and Radiation. Since intentionally produced nanomaterials are expected to be
released to and exist in the environment as particles in most cases, it is wise to investigate
applicability of these other models. In fact it can be reasoned that the most useful modeling tools
for exposure assessment of nanomaterials are likely to be found not in the area of environmental
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