Radiation - No Dose Threshold

Duh!  As long as one photon can cause DNA damage and DNA repair is imperfect, there will always be a non-zero cancer risk or genetic risk associated with the photon.

Frequently, not-so-bright people arguing for a threshold point to areas where the natural radioactivity is higher than average.  They claim living there is "safe" because...people live there. Or something.  Usually it involves the ecologic fallacy.

Recently, two scientists did a meta-analysis of other studies involving this subject and concluded no dose threshold.

Of course, there will be those folks who will see what the lowest radiation level was in that study, and then they'll claim that there is a threshold for doses below that level.