Fig. 2

Transmission electron micrographs of A549 cells treated for 24 h with 50 μg/ml of the indicated NMs and untreated control. Low and high magnification images of the selected area (dashed box) are shown. All NMs are readily taken up by the cells and accumulate primarily in membrane-enclosed organelles. Arrowheads indicate examples of NM clusters. Arrow points to CeO₂ stamps in the nucleus. Asterisks indicate examples of non-membrane-enclosed NMs. N (nucleus), L (lysosomes) and aV (autophagic-like vacuoles). Scalebars: 5 μm in low magnifications, 100 nm in high magnifications and 400 nm in high magnification for control (unexposed cells)