Continuity mistake: Tina's grip on Lana's necklace changes as she stands over Lana's body. (00:37:30)
Continuity mistake: When "Lex" threatens the bank manager, he points the gun at his face, but the next shot on the manager shows the gun at his throat. (00:01:35)
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