A great effort is being done by the scientists to increase our knowledge on the role of nanoparticlesassociated genotoxic and carcinogenic effects [1, 2] . Although important research activity took place in this area for >10 years, most of the findings concerning to the genotoxic and cell transforming potential of NPs are limited to short-term in vitro studies [3, 4] . Comprehensively, acute or short-term studies use high environmentally irrelevant single doses to study the adverse effects of

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... gineered NPs, which could not be enough to draw plausible conclusions about the potential human health risk of NPs exposure [5] . Until now, only a few in vitro long-term exposure studies have been carried out with NPs [6, 7, 8, 9] . Keeping this in mind, it seems necessary to increase the amount of in vitro investigations focusing on long-term or chronic exposures at sub-toxic doses.