Liquid-phase transmission electron microscopy (LP-TEM) emerged as a cutting-edge in situ technique for investigation of processes at the nanoscale. Particularly in the fields of catalysis, energy materials and storage, soft-matter studies, or virology, LP-TEM has been enabling unprecedented insights into fundamental processes, such as non-classical crystallization pathways and nanostructure self-assembly. However, inherent inelastic electron-matter interactions influence the Gibbs free energy landscape. To enable LP-TEM becoming a standard characterization method this needs to be accounted for appropriately. Besides electron beam-induced heating, radiolysis is a crucial factor during LP-TEM, even when radical scavengers are utilized or radiolytic shielding via graphene membranes is harnessed. Moreover, radiochemistry has been identified as a prime driving force to study both reductive formation, and oxidative etching of metallic nanostructures. Operating between the poles of mitigation and utilization of radiation effects is not limited to LP-TEM but is relevant for many experiments investigating structures or processes in liquids utilizing ionizing radiation. Thus, understanding the radiochemistry is the key for appropriate experimental design and interpretation.