Fantastic voyage and opportunities of engineered nanomaterials: What are the potential risks of occupational exposures?

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In his legendary lecture at Caltech 50 years ago, Richard P. Feynman, introducing a new concept of nano-sized materials, noted: “.... a point that is most important is that it would have an enormous number of technical applications. What I want to talk about is the problem of manipulating and controlling things on a small scale.” This prediction turned out to be a prophecy, and today we appreciate that quantum properties strongly affect physical and chemical properties of nanoscale objects, conferring electrical, optical, and magnetic features not present in materials at a larger scale. Based on this, devices enormously smaller than before have been created, which may have a potentially huge impact on engineering, chemistry, medicine, and computer technology. Not surprisingly, nanodevices have already found different applications as diagnostic and therapeutic tools in biomedicine and in numerous consumer products. The applications in biomedicine range from novel approaches to the design of artificial organs and tissues for replacement therapies to nanorobotic biosensors, diagnostic devices, and miniscule vehicles for targeted drug delivery.1 Different types of nanoparticles are being considered, including carbon-based structures, such as carbon nanotubes, carbon nanocapsules, and fullerenes, or spherical lipid-based liposomes, which are already in use for numerous applications in drug delivery and in cosmetic products. Other types of nanomaterials envisioned for biomedical and other applications are based on metals and their oxides as well as ceramics. Nanotechnology industry is projected to exceed $1 trillion by 2015.2
The linear dimensions of nanomaterials are in the same range as the major cellular machineries and their components. Therefore, nano-sized materials are likely to interact and, more importantly, interfere with cellular organization and affect biological functions in ways that are unknown and cannot be deduced from previous experience with macro- or microsized objects. In addition, specific features of nanoelements may be realized through their unique electron donor/acceptor properties resulting in unexpected effects on redox balance and redox reactions in cells. This, again, emphasizes the poor predictive power of traditional toxicology as the basis for assessments potential damaging effects of newly created nanomaterials. These unusual and unpredictable properties of nanomaterials fostered the emergence of a new subdiscipline in the field of toxicology, nanotoxicology.3 The latter can be defined as the field of science that investigates mechanisms and pathways through which nanoparticles or complex engineered nanostructures may interfere with the structural and functional organization of cellular and extracellular nano-sized machineries leading to cytotoxicity with adverse effects on human health and the environment.4 This definition places emphasis on the specific responses that are directly related to the scaling and dimensions of nanomaterials. Recently, cases of such “molecular interferences” have been documented. For example, the narrow diameter (2–3 nm) and significant length (hundreds of nm) of single-walled carbon nanotubes (SWCNT) may facilitate their interaction with elongated biological structures of the mitotic apparatus. Indeed, in cultured human airway epithelial cells, SWCNT have been shown to cause fragmentation of centrosomes, multiple mitotic spindle poles, anaphase bridges, and aneuploid chromosomes. Confocal microscopy revealed an association of carbon nanotubes with cellular and mitotic tubulin as well as with chromatin.5 It is noteworthy that studies of asbestos (crocidolite) fibers published almost 25 years ago demonstrated that Chinese hamster ovary cells, which contained fibers that were longer or equivalent to the diameter of the mitotic cell (20 μm), also showed different forms of mitotic abnormalities.6
Five organ systems—lung, skin, gastrointestinal tract, nasal olfactory structures, and eyes—are the major portals through which nanoparticles can enter the body as a result of inadvertent occupational or environmental exposures.
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