In toxicology, electron microscopy is used to examine the effects of toxic substances at the cellular and sub-cellular levels. It helps toxicologists to visualize the damage caused by toxic substances to organelles, such as mitochondria and the endoplasmic reticulum, and to identify the presence of nanoparticles and other foreign materials within cells. By providing such detailed imagery, electron microscopy aids in understanding the mechanisms of toxicity and in the development of therapeutic strategies.