Radio active elements is the name for atomic elements with unstable nucleus. This nucleus can undergo different processes, each of them probably having different health effects.
I can't find studies or enough information about the effect of radioactivity (radiation coming from unstable nuclei) in low amount/short exposure either in general or for each type of process. Probably this information is just not easy to get. I'm only trusting this source so far.
I'm in italy and close to the island of Ischia, there is radioactive water (thermal water, and maybe linked to the natural life of a volcano). People use it, and it seems to be that short time exposure may not be harmful.