Nanotechnology White Paper - US Environmental Protection Agency

EPA Nanotechnology White Paper
Kreyling, 2004). The European Union’s Scientific Committee on Emerging and Newly
Identified Health Risks (SCENIHR, 2006) has also overviewed existing data on nanomaterials,
data gaps, and issues to be considered in conducting risk assessments on nanomaterials.
The purpose of this chapter is to briefly review the state of knowledge regarding the
components needed to conduct a risk assessment on nanomaterials. The following key aspects of
risk assessment are addressed as they relate to nanomaterials: chemical identification and
physical properties characterization, environmental fate, environmental detection and analysis,
human exposure, human health effects, and ecological effects. Each of these aspects is discussed
by providing a synopsis of key existing information on each topic.
3.2 Chemical Identification and Characterization of Nanomaterials
The identification and characterization of chemical substances and materials is an
important first step in assessing their risk. Understanding the physical and chemical properties in
particular is necessary in the evaluation of hazard (both toxicological and ecological) and
exposure (all routes). Chemical properties that are important in the characterization of discrete
chemical substances include, but are not limited to, composition, structure, molecular weight,
melting point, boiling point, vapor pressure, octanol-water partition coefficient, water solubility,
reactivity, and stability. In addition, information on a substance’s manufacture and formulation
is important in understanding purity, product variability, performance, and use.
The diversity and complexity of nanomaterials makes chemical identification and
characterization not only more important but also more difficult. A broader spectrum of
properties will be needed to sufficiently characterize a given nanomaterial for the purposes of
evaluating hazard and assessing risk. Chemical properties such as those listed above may be
important for some nanomaterials, but other properties such as particle size and size distribution,
surface/volume ratio, shape, electronic properties, surface characteristics, state of
dispersion/agglomeration and conductivity are also expected to be important for the majority of
nanoparticles. Figure 17 provides an illustration of different states of aggregation nanoparticles.
Powers et al. (2006) provides a discussion of nanoparticle properties that may be important in
understanding their effects and methods to measure them.
31