Revealing mistake: While Lana is listening to her Mother's graduation speech she reaches up to her neck for her meteor rock necklace. Her hands do not reach far enough back to unclasp the necklace yet the necklace comes off anyway.
Revealing mistake: As Tina/Clark tries to run over Martha, there is a shot of Tina/Clark up close in the truck, and the gear shift is still in park.
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