Of course “extremely low”. But there are no safe radiation limits anymore:
The cesium is biological similar to the potassium and the human body can not distinguish between the potassium and cesium.
The body takes it on the breath and the food. You can not protect yourself: http://tekknorg.wordpress.com/2011/03/19/effect-of-cesium-and-strontium-on-japanese-children-japanese-officals-irresponsible/