Skinwalker - S2-E10
Plot hole: Chloe says the coroner found teeth marks on the foreman's bones. During the attack, at the beginning of the episode, the foreman only got a couple of scratches on his face and the rest of his clothes were perfectly fine and hadn't, in any way, been torn up. It would have taken the wolf tearing through the clothes, through the skin and, finally, through the muscle to leave any teeth marks on the foreman's bones and that did not happen.
Answer: The kryptonite only creates mutations when it reacts with the environment and an individual. Remember, the FDA and several environmental groups did check out Smallville after the meteor shower, but found no danger in the rocks. Obviously they're not always emitting mutating rays, or all the flora and fauna of the surrounding area would be horribly mutated.
Phoenix