Continuity mistake: When Clark is faced with Nathan Dean at the Auto Wrecking lot, Nathan says "In a minute, neither one of you will care," (regarding Pete Ross' whereabouts). The next shot is of the blue car that Pete is trapped in with the windows blown out. Then the shot goes back to Clark and Nathan, and the cars fall onto Nathan. Clark is then listening for Pete and when we see a shot of the blue car being crushed, this time we see the windows being smashed.
Continuity mistake: Martha asks Clark to come out after he gets glasses. In the shot showing all three of them, Clark comes into view on the left side of the screen and is turned toward his parents. The very next shot shows he is just walking through the door of the optometrist and turned away from his parents as he closes the door.
Continuity mistake: When Lionel and Lex are talking, after they sit down, near the end of the conversation, Lionel asks who Lex's source is. Lex is looking straight ahead. In the next shot, we see Lex turn his head to face his father. In the next shot, Lex is looking straight ahead again.
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