Cell death after exposure to particles. Panels A and B show flow cytometry analyses of cells stained with annexin V and PI after exposure to ZnO and CuO NPs at (A) 10 μg/mL and (B) 20 μg/mL, either alone or in mixture with DEPs (100 μg/mL). Statistically significant with respect to the control according to one-way ANOVA, ** p < 0.01, * p < 0.05, and **** p < 0.0001 vs. control. (C) Morphological analysis. Microscope images of A549 cells, stained with hematoxylin/eosin: (a) control; (b) ZnO (20 μg/mL); (c) DEP + ZnO (20 μg/mL); (d) CuO (20 μg/mL); (e) DEP + CuO (20 μg/mL); (f) DEPs (100 μg/mL); scale bar = 20 μm.