Skinwalker - S2-E10
Visible crew/equipment: After Joseph gets locked out of the construction site, the worker, who locked him out, walks away. All the other workers at the site are gone, but when the shot returns to Joseph you can see the shoulder of someone standing between Joseph and the gate even though there should be nobody there.
Skinwalker - S2-E10
Visible crew/equipment: After Kyla dies the scene goes to the construction site as Martha and Lionel get out of a SUV. As Martha gets out you can see the camera and film crew reflected in the window of the SUV.
Visible crew/equipment: After the scene transition from when Clark throws Jonathan into the truck after being exposed to Red Kryptonite, the camera pans around Jonathan with his shirt off; on the left-side of the screen we see a man with sunglasses on who has no earthly right to be there just randomly on the Kent Farm. (00:16:23)
Skinwalker - S2-E10
Visible crew/equipment: While Clark and Pete are riding dirt bikes, you can see a crew-member in a green jacket in the bottom-right-hand corner of the screen in the shot where they go off the jump. In the next shot he has disappeared.
Visible crew/equipment: When Martha and Jonathan are talking about Lionel's job offer in the kitchen, a boom mic can be seen in upper left corner of the screen.
Visible crew/equipment: When Tina, disguised as Lana, throws Pete against the lockers, you can easily see that it's Pete's stunt double.
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