The radiation passes through the food, none of it stays there. (And the sun irradiates food too, just not with anything like the same intensity.) I believe the concern is over free radicals caused by reactions within the food to the radiation. I haven't seen any information on whether or not the possible dangers of these free radicals, and which foods might be more of a problem, have been studied. (Not that it doesn't exist - sounds like what Mark would have found in his research.)