Increasing utilizations of nanomaterials in the industrial as well as consumer products increase the possibilities of environmental and occupational human exposures. Due to this fact nanoparticles (NPs) have become candidates for the risk assessment. Among the possible exposure routes, inhalation represents the most important route of non intentional exposure to NPs. There are increasing evidences that NPs exhibit ability to cross biological barriers getting access to the bloodstream and secondary target organs where they could accumulate. The knowledge of the behaviour and fate of NPs especially insoluble NPs is of prime interest to assess the pathological consequences linked to long term exposure. The surface area and reactivity of particles increase many fold relative to particle mass as particle size is reduced. Together with chemical composition, they constitute important determinants of NPs toxicity. They also contribute in the production of reactive oxygen species leading to the toxicological outcomes induced by NPs. According to the level of oxidative stress, cellular responses differ from effective antioxidant defence at low level to cell death at high levels going through inflammatory response, specific signalling pathways and gene expression being involved at each step. The potentially deleterious effects of NPs require further studies in order to build on our mechanistic understanding of the toxicological events in which they can be implicated and the development of methodological tools to face the huge variety of NPs to be evaluated.

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