The natural life cycle of many animals is too short to significantly have issues. Contrary to comics, most mutations effect embryos which are aborted. Those that live past birth are usually quickly consumed by predators or simply die shortly after birth. Most (all?) smoke detectors no longer use cesium; see nuclear boy scout. Humans currently live there too. So long as they are not consuming food (some are) from the contaminated areas, they shouldn't have issues. Long term tumor risks over an 80-100 human lifespan is not the same as a 3-8 year lifespan common to many wild animals. Predation is an important aspect of natural wildlife life cycles. All of which ignores, there are multiple radiation exposure models. We use the zero threshold model even though it's completely wrong. It's used because it's extremely conservative. Additionally, the other models require refinement, which requires human subjects.