Environmental Risks of Nanomaterials - Nanotechnologies for Water Environment Applications - page 601

17.4.1 Risk Assessment of NMs
A risk assessment is the evaluation of scientific information on the hazardous
properties of NMs, the dose-response relationship, and the extent of exposure of humans
or environmental receptors to those NMs (USEPA, 2007). Generally, a toxicity
screening strategy include three key elements of physicochemical characterization of
NMs, in vitro assays (cellular and noncellular), and in vivo studies (Oberdörster et al.,
2005a). The current status of NMs with respect to these elements is briefly described
below.
17.4.1.1 Chemical Analysis of NMs
Chemical analysis for understanding physical and chemical properties of NMs is
very important and necessary in the evaluation of toxicological and ecological hazards
and exposure routes. The physical and chemical properties mainly include molecular
weight, melting point, boiling point, vapor pressure, octanol-water partition coefficient,
water solubility, reactivity, stability, as well as additional information on purity, product
variability, performance, and use. For NMs, more information, such as the particle size
and distribution, surface/volume ratio, magnetic properties, coatings, and conductivity,
is included. Currently, material safety data sheets (MSDS) for most NMs list properties
and restriction which are identical to those given for the bulk material. Thus, workers
making and using NMs have no formal requirements for safety precautions beyond those
adopted for identically bulk materials.
A given NM can be produced by several different manufacturing processes with
different physical-chemical properties. For example, SWCNTs can be produced by four
different processes that can generate products with different sizes, shapes, and
compositions, and potentially different ecological and toxicological properties. Existing
physical-chemical property test methods may not be adequate for sufficiently
characterizing various NMs for risk assessment. It is clear that chemical properties such
as partition coefficients and vapor pressures are insufficient. Thus, the diversity and
complexity of NMs makes chemical analysis not only more important but also more
difficult. Alternative methods for testing properties of NMs need to be developed.
17.4.1.2 Environmental Fate of NMs
The higher mobility of NMs in the environment implies a greater potential for
exposure/release as they are dispersed over greater distances and their effective
persistence in the environment increases. Potential direct and/or indirect releases of NMs
to the environment (e.g., the atmosphere, soils, and water) are high from the
manufacture and processing of NMs, chemical and material manufacturing processes,
remediation of soil-contaminated sites, and NMs for consumer uses (e.g.,