Continuity mistake: As Chloe leaves Clark calls out her name. In the shot from Chloe's side of the room, Clark is holding the pitchfork horizontally low in front of him. The shot switches, as Chloe finishes her turn, and now Clark is holding the pitchfork with his arm bent so that the pitchfork is no longer low in front of his waist.
Tempest (1) - S1-E21
Continuity mistake: The way the pillar is on top of Lionel changes in the scene. In the first shot, he's on his side and it lands on his hip. In the next shot he's now on his back and the pillar is going somewhat across his body. In the wide shot of him as the roof falls, the pillar is below his belt, almost perpendicular to his body. Then back to being on his stomach and part of his chest.
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