Environmental Risks of Nanomaterials - Nanotechnologies for Water Environment Applications - page 600

multifocal granulomas, but such effect was not progressive beyond 1 month post
exposure. In addition, the CNTs were found to be more toxic to animal lung than black
carbon or ultrafine quartz particles.
To summarize, NMs may enter the cell through caveolar/endocytotic routes to
embed themselves within the functional machinery of the cell. At the cellular level,
interactions of NPs with cell components occur via endocytosis. The endocytotic process
can lead to the endosomal and lysosomal compartments inside the cell and disrupt the
endosomal/lysosomal system (Panyam and Labhasetwar 2003; Panyam et al., 2003). In
addition, NMs may directly interact with cellular components, including membrane
transporters, cytoskeleton, mitochondria, and specific receptors (Moore et al., 2004).
Some reasonable predictions about potential hazards of NMs have been proposed based
on their size, surface charges and chemical reactivity (Hoet et al., 2004; Warheit, 2004).
While NPs may be more toxic than the bulk counterpart, NP composition and surface
chemistry, in some cases, may be even more important to toxicological properties than
size. NMs may also results in other forms of injury, such as protein denaturation,
membrane damage, DNA damage, immune reactivity, and the formation of foreign body
granulomas (Nel et al., 2006; Wiesner et al., 2006). NMs toxicity to algae, plants, and
fungi can be found in a recent review article (Navarro et al., 2008).
17.4 Risk Management
In light of the aforementioned discussions, NMs are likely to cause different
impacts on living beings, occupation health and the environment, depending on the size,
shape and chemical composition of the NMs. There is great uncertainty about what the
actual risks of NMs to living beings, our society, and the environment are. As a result, it
is more difficult for risk management of NMs than for that of normal sized materials. A
proper risk evaluation and management for NMs is often hampered by the following
reasons: (1) incomplete physicochemical property description of the NMs, (2)
uncertainty of expected exposure and potential hazard in health, ecology, and the
environment effects, (3) incomplete knowledge of nanotoxicology and unique properties
and potential impacts on fate, exposure, and toxicity, and (4) uncertainty of the result
extrapolation from experimental animals to humans.
Accordingly, a proactive approach is appropriate in risk management of NMs.
Except using the principles of pollution prevention during NMs manufacturing processes,
our understandings in regard to the toxicity of NMs, dose metrics, probable exposure
pathways, and environmental fate and transport of NMs are needed for the risk
management process. In general, the risk management mainly includes risk assessment,
health and environmental impact, toxicity study, and legislation definition.