Introduction - Nanotechnologies for Water Environment Applications - page 9

at 5 nm in size; the question is, do these relatively nontoxic materials become toxic on
the nanoscale? There is some controversy surrounding sunscreens containing nano-
sized particles of TiO 2 or zinc oxide, which can absorb directly into the skin and can
readily enter the bloodstream and other body tissues, and have not been proven safe.
Therefore, the true issue associated with implications of NM applications is that the
technology for creating NMs and the applications of them are far outpacing our
knowledge and regulations about their potential toxicity.
Health and Safety Issues. Accumulated evidence indicates that the adsorption
of NPs via the lung, skin and gut can occur. However, a clear understanding of their
distribution in the body (i.e., toxic kinetics) is not available, which requires (a)
identification of potential target organs/tissues for toxicity assessment, (b) understanding
of inter and intracellular transport and localization of NPs and their cellular toxicity.
Clinical and experimental studies indicate that an ability to generate reactive oxygen
species (ROS) and oxidative stress play a role in the ability of NPs to induce the toxic
effects. However, inflammatory effects, genotoxicity, and physical piercing of
membranes and other cell structures and molecules can all apply to NPs. The specific
properties related to NM's behavior and toxic effects to living organisms are as yet
poorly understood, such as the deposition, distribution, toxicity, pathogenicity and
translocation potential and pathways for NPs within the host organism. For example,
dermal uptake, penetration and toxicity of TiO 2 NPs in the skin still are not clear.
Currently, research relating to the toxicology of NMs is focusing on discovering
(a) what controls the toxicity of representative NPs [TiO 2 , carbon black, C 60 , quantum
dots, polystyrene particles, carbon nanotubes (single-walled and multi-walled), metal
oxides (e.g., NZVI), and 100 nm PLGA (poly (D,L-lactic co-glycide) acid) NPs], (b)
whether there are unknown factors, and (c) what the mechanisms are involved in. Both
in vitro and in vivo methods are used to examine the toxicological properties of NPs.
The methods will vary from particle to particle depending on mode of exposure and use.
Moreover, frameworks allowing the extrapolation of in vitro results to natural systems or
to assess the risks of forthcoming NMs based on previous knowledge are needed
(DEFRA, 2006; Navarro et al., 2008).
Environmental Issues . Considerable studies have been conducted on the uptake,
toxicity and effects of NPs on groundwater, surface water, soil microorganisms, animals,
and plants, especially in the context of remediation, water and wastewater treatment, and
air pollution control. Most of these studies are conducted within the laboratories with
bench-scale systems. Sufficient information is not available on evaluation of the whole
life cycle of NMs, including their fabrication, storage/distribution, application/potential
abuse, and disposal. The impact on human and natural ecosystems may be different at
different stages of the life cycle.