Assessment of Progress - Research Progress on Environmental Health and Safety Aspects of Engineered Nanomaterials - page 31

Models are needed for accurate prediction of nanomaterial releases, environmental
concentrations, and human and ecosystem exposures. Models of releases also are needed to identify the
form and speciation of released nanomaterials. To date, modeling efforts appear to be confined to specific
release points and routes of exposure (such as inhalation exposure in the workplace and releases in
wastewater-treatment plant effluent discharges). Further progress has not been initiated, because of the
lack of information on inventories in the value chains highlighted above. Because of the lack of
quantitative information throughout the life cycle of ENMs on which to build such models, progress in
this indicator is denoted as red.
Processes That Affect Both Exposure and Hazard
In its first report, the committee highlighted the need to identify the critical nanomaterial
interactions that affect ENM behaviors. It recommended identifying cross-cutting processes (for example,
agglomeration, aggregation, dissolution, and deposition) that are common to assessing exposure and
assessing hazard. Identifying nanomaterial interactions requires cataloging the types of ENM
transformations in complex matrices and the time scales associated with the transformations, developing
instrumentation to monitor transformations in vivo or in complex environmental media, and developing
models to predict ENM behaviors. Integral to these efforts are the need to develop the ontology to
describe “transformed” nanomaterials and the need to develop the infrastructure to archive data that
enables model development and identification of these processes. Progress ranged from yellow for
initiation of basic studies that are beginning to characterize likely types of ENM transformations and to
require additional study and for studies that begin to relate ENM properties to observed effects in more
complex systems to red for development of new instrumentation to measure transformations in situ, in
vivo, or on single particles. The committee also notes that the data generated have not been effectively
used to develop and validate the models, because of the absence of a central structured database for
consistent documentation of research results.
 Steps taken toward development of a knowledge infrastructure able to describe the diversity
and dynamics of nanomaterials and their transformations in complex biologic and environmental media
In its first report, the committee indicated the need to develop a knowledge infrastructure to
measure and describe nanomaterial behaviors, including transformations that affect exposure and hazard.
The types and nature of the transformations that affect both exposure and toxicity studies (for example,
aggregation, agglomeration, oxidation, reduction, dissolution, adsorption of macromolecules, and
interactions of ENMs with cell membranes) have been documented in many studies and review articles
(Verma and Stellacci 2009; Wiesner et al. 2009; Levard et al. 2012; Lowry et al. 2012a; Moghadam et al.
2012; Mu et al. 2012; Nowack et al. 2012; Cheng et al. 2013; Zhu et al. 2013). The importance of the
components of the media in which ENMs are dispersed is also well established (Maiorano et al. 2010).
Despite a large volume of laboratory-based research, the committee classifies progress as yellow because
no knowledge base exists to describe and understand these transformations in general. Most studies have
examined specific conditions, so current understanding of ENM behaviors is system-specific. Knowledge
of the mechanisms behind the transformations is also often incomplete. Several nascent efforts are under
way to characterize systematically and precisely how various solution conditions (for example, dissolved
solutes, pH, and redox state) and ENM properties affect transformations that will allow the development
of predictive models (Ottofuelling et al. 2011; Nel et al. 2013). However, the data infrastructure needed to
share the results is not yet widely available, as highlighted above. Development of the infrastructure and
data-sharing are complicated by the highly variable nature of the transformations and by the lack of an
ontology to describe the “state” of a fully or partially transformed ENM. Finally, there is no way to
characterize many of the transformations in relevant media at realistic concentrations. In some cases, that