Paper! Oh, wait....
So, it has been dry, so beneficial bacteria is gone. What “I” would do (I know many will say bleach etc) would be to put it in a brute, fill with water (rodi or sea-water) and put a powerhead in it. If nasty stuff grows, then you will want to basically make them sterile/dry rocks and start from scratch, but of the tank they came from was in good working order, letting the dead organics fall off in a brute with water for awhile should make them safe to drop right into a tank