In some of the Creatures games, radiation is an environmental hazard that will give your Norns, Grendels, and Ettins a toxin known as heavy metals.
The Grendels in Creatures 2 frequently suffer from heavy metal poisoning due to the Grendel mother's proximity to the volcano, which is the primary source of radiation/heavy metals in Creatures 2. This slowly kills their bones (the game's name for bone marrow) causing potentially fatal immunosuppression. Any creature unlucky to wander into the vicinity of the volcano can suffer such a fate, so it's important to keep an eye on all in the area! The Radiation Remover can remove this hazard. Some radiation can also occur near the surface, with radiation levels being affected by the season and time of day.
In Creatures 3 and Docking Station, radiation primarily comes from third party agents, one creative example being the Atomic Bomb. In these later games, the heavy metal poisoning resulting from radiation will largely affect reproductive function, though it can still affect bone marrow. Toxic Norns derive benefit from exposure to heavy metals, just as they do with other toxins. Third party genetic breeds may have unexpected reactions.
For information about relevant real-world subjects, see the Wikpedia articles on Ionizing radiation and Heavy metals (may contain or link to graphic content, reader discretion advised).