Here is a theory on the difference between chemical mutations and radiation mutations. In radiation mutations bits of the genes get knocked off resulting in hair loss skin problems birth defects, and its all a loss of stuff not a gain of stuff, so its impossible for super heroes to be made by radiation. With chemical mutation the body finds an unidentified gene or protein and thinks it means an extra leg finger muscle skin organ or bone, and causes a mess up thats why you find frogs with extra legs in polluted ponds. These are just theories so if any one who is reading this knows anything post it as a comment.