Adding an activated charcoal bed would take care of the radioactive Iodines, too. I guess you would have to keep the activated charcoal in sealed bags, and pour it into the bed if it ever became necessary. (I used to do that stuff at a nuclear power plant.)
There is one problem, though. If the activated charcoal bed gets too "loaded up" with radioactive Iodines, it gets hot and catches fire. Bad thing...