Continuity mistake: As Lionel says "Good morning, Miss Sullivan." there is a camera change from Chloe's left to her right. When the camera is on the left, her left arm is down. When the camera jumps to her right her left arm is now in the middle of placing something high up on the layout board she is using.
Continuity mistake: As Pete gets into his car the shadow from the car is extending out away from the passenger side of the car. As Pete starts to drive off, just a few seconds later, the shadow is now extending out past the back of his car.
Continuity mistake: Just before Lex has his father arrested they are talking while Lionel sits behind his desk. In the shot of Lionel from his side of the desk there is a flat panel monitor behind his keyboard. In shots from Lex's side of the desk the monitor is gone. It returns as FBI agent Loder walks in and Lex stands up.
Continuity mistake: When Lex tells Clark about Lionel finding the wire, Clark moves over to Lex and says that finding something incriminating on Lionel shouldn't be too difficult. Between shots, Lex and Clark's positions change in relation to each other.
Continuity mistake: While Clark and Pete are playing basketball, in the wide shot Clark and Pete, and the side of the barn where the hoop is, are in full sunlight. When the shot zooms in Clark and the barn are now in shadow.
Continuity mistake: After Lionel finds out about the wire that Lex has been wearing, he sits down and tells Lex to get out. As Lex leaves, in the wide shot, Lionel drops his hands down to his lap. In the zoomed in shot Lionel's hands are up to his face as he plays with the wire. There was no time for him to make that move between shots.
Continuity mistake: As Emily lies on the ground unconscious after being hit with the water, she is first shown lying there with her right arm bent up and her hand up by her head. After a quick shot of Clark she now has her right hand down by her side.
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