Visible crew/equipment: As the FBI search the Kent's house, you can see the shadow of the camera as it moves from the kitchen to the hallway next to the stairs. The shadow appears on the right side of the arch between the kitchen and hallway. (00:17:50)
Continuity mistake: As Clark jumps the fence, to stop Jonathan from falling, you can see Martha is standing in sunshine with the shadow of the barn well away from her. When Clark actually catches Jonathan suddenly Martha is standing in the shadow of the barn.
Continuity mistake: When the weather vane falls to the ground the rooster portion of the vane gets bent. When Jonathan picks it up and starts to angrily walk away from Martha and Clark it is straightened.
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