Continuity mistake: When Clark exits the phone booth wearing his blue shirt, only the neck button is unbuttoned in the wide shot. Immediately in the next close-up shot, two buttons are undone. Then in the next shot of Clark's front side, the shirt is back to only the neck button being undone. (00:02:27)
Turbulence - S8-E16
Other mistake: In the article about the plane crash, the last paragraph starts to repeat the same sentence. After is says Mercer took over the operation, it repeats that she started in collaboration with Lex.
Other mistake: After Clark enters the phone booth, he begins to change out of his red shirt. The phone booth is mostly frosted glass, but it is possible to make out that Clark only becomes bare-chested before the next shot when he comes out of the phone booth with the blue shirt on. (00:02:14)
Plot hole: Though it fits the general plot of Davis always being first on scene, in the real world no on-duty paramedic drives the ambulance alone. There will always be a minimum of two EMTs per ambulance, one to drive and one to tend the patient. The only time a paramedic or other EMT will be alone is if they arrived on the scene in their own vehicle.
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