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