I would worry that animals would accumulate radiation in their bodies over time, similar to how tuna can end up with large amounts of mercury or other toxic metals.
Only if it bioaccumulates faster than the half-life of the isotope reduces its presence. Strontium-90, e.g. has a half life of 28.5 years and a biological half life of 30 years http://hpschapters.org/northcarolina/NSDS/strontium.pdf
