Plot hole: Chloe has to use Lex's thumbprint to access the safe inside level 3. She gets his fingerprints by lifting it off of the flashlight he picked up for her earlier in the caves. The problem is when Lex picked up the flashlight and gave it to Chloe he had only touched the back half of the flashlight, but when Chloe lifts Lex's print she gets it from the opposite end. Since Lex did not touch that end there should be no fingerprints for her to lift and use on the security door.
Continuity mistake: When Clark's parent show up at the house Clark hurries up and acts busy. He grabs 4 boards and moves them from one part of the kitchen to the other and leans them up against the wall. When Clark turns around to face his parents there are only 2 boards leaning on the wall.
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