Heavy metals are found naturally on Earth and exposure to them in the living environment is increasing as a consequence of human activity. The toxicity of six different metal oxide nanoparticles (NP) at different points in time was compared using resazurin assay. After incubating Caco2 and A549 cells with 100 lg/mL of Sb 2 O 3 , Mn 3 O 4 and TiO 2 nanoparticles (NPs) for 24 h no toxic effects were observed while Co 3 O 4 and ZnO NPs had moderate effects and CuO NPs were toxic below 100 lg/mL (24 h EC 25 = 11 for A549 and 71 lg/mL for Caco2). The long-term monitoring (up to 9 days) of cells to NPs revealed that the toxic effects of Mn 3 O 4 and Sb 2 O 3 NPs remarkably increased over time. The 9 day EC 50 values for Sb 2 O 3 NPs were 22 and 48 lg/mL for A549 and Caco2 cells; and for Mn 3 O 4 NPs were 47 and 29 lg/mL for A549 and Caco2 cells, respectively. In general, the sensitivity of the cell lines in the resazurin assay was comparable. Trans epithelial electrical resistance (TEER) measurements were performed for both cell types exposed to Co 3 O 4 , Sb 2 O 3 and CuO NPs. In TEER assay, the Caco2 cells were more susceptible to the toxic effects of these NPs than A549 cells, where the most toxic NPs were the Sb 2 O 3 NPs: the permeability of the Caco2 cell layer exposed to 10 lg/mL Sb 2 O 3 NPs already increased after 24 h of exposure.Electronic supplementary material The online version of this article
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