Engineered Nanomaterials as Emerging Contaminants in Water - Nanotechnologies for Water Environment Applications - page 581

natural NMs can be applied to quantify the size distribution and mass concentrations of
engineered NMs. Most of these techniques place multiple systems (size separation -
detection) in series. There suitability to detect environmentally relevant concentrations
of engineered NMs in complex matrices remains untested, largely because release of
engineered NMs into the environment has largely not yet occurred. As the biological
effects of NMs become better defined, it may be necessary to measure additional
properties other than size and mass concentration (e.g., crystal structure, shape, surface
area, etc).
Fourth, can current fate and transport models be used to represent processes and
predict the movement of engineered NMs within aquatic systems? In simple, small
scale systems complex mechanistic physicochemical and transport models developed to
understand movement of natural NMs appear valid for engineered NMs. However,
larger ecosystem scale models will likely have to be developed particularly for NMs.
Existing pollutant transport models for organic dissolved chemical pollutants rely
largely upon first-principle properties intrinsic to the pollutants (e.g., solubility,
hydrophobicity) which are coupled with partition models (e.g., air-water, solid-water,
bioaccumulation) and transformation models (e.g., hydrolysis, photolysis,
biodegradation) to predict the movement and disposition of pollutants in the ecosystem.
Preliminary evidence by our research group suggests partition models may also be
viable for predicting NM fate, but methods for determining appropriate partition
surrogates (e.g., octanol-water, lipid-water) and methods for conducting such
experiments remain ill-defined.
Research over the next decade should develop answers to these important
questions. A successful outcome of such efforts should result in understanding the
ultimate disposition of engineered NMs before they are mass produced. While some
refractory engineered NMs may ultimately reside in stream and ocean sediment, others
will undergo dissolution, functionalization or other transformations. By beginning to
understand issues raised in this chapter, the evolutionary progression of engineered NMs
as emerging contaminants will continue along a predictable time series (Figure 16.1) as
more information is obtained that help to characterize the risk (Figure 16.6) of
engineered NMs in aquatic systems.
16.8 Acknowledgements
This research was partially supported by the USEPA (grant RD831713 and
RD833322) and the Water Environment Research Foundations Paul L. Busch Award for
Innovation in Research (2006). Contributions from graduate students (Yang Zhang,
Troy Benn, Ayla Kiser, Aaron Dotson, Brian Koeneman) and faculty collaborators (John
Crittenden, Bruce Rittmann, Yongsheng Chen, Pierre Herckes, Jonathan Posner, David