I would be much more concerned about the effects of some of the bad sunburns I had as a kid than the effects of any new post-disaster background radiation to be found in Japan.
The radioactive cesium is in the food supply - it’s not agreeing to stay low or in the background. It’s been detected in beef, wheat, produce, and tea crops. So while the background radiation increase is physically damaging to human health, they also have to worry about eating, drinking and breathing isotopes. Japan isn’t helping them out by burning radioactive waste which puts the isotopes back into the air but then they have three molten fuel cores that are now somewhere below the reactors and are freely putting contaminants into the air for the foreseeable future. So the problem is not limited to the unfortunate increase in background radiation, damaging as that is. There’s alot of speculation about what might happen if/when the molten cores reach japan’s water table.