Continuity mistake: As Lana starts her second swing at Chloe with the axe while the camera is in front of Lana Chloe is just barely getting up and is still close to the floor. The camera switches in mid-swing and suddenly Chloe is completely standing and is able to jump back to dodge the swing.
Continuity mistake: When Molly first starts flipping through the disks for Lex, she has a ring on her left ring finger. After Lex talks about just getting back Molly is shown still flipping through the disks only now the ring is gone.
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