Intracellular localization of AgNPs and accumulation of autophagosomes and autolysosomes. A549 cells were treated with silver nanoparticles (AgNPs) for 24 h and then processed for transmission electron microscopy (TEM) sections. TEM images of ultramicrotome slices of A549 cells without AgNPs (A), internalization of biologically synthesized AgNPs (bio-AgNPs) (B), and internalization of chemically synthesized AgNPs (chem-AgNPs) within the cells (C). Bio-AgNPs induces accumulation of autophagosomes (black arrow) and autolysosomes (white arrow) in cells treated with bio-AgNPs for 24 h (D). Autolysosomes and vesicular structures consistent with autophagy were detected in cells treated with bio-AgNPs (E) and chem-AgNPs (F).