Other mistake: In the flashback to 1961, "Splendor in the Grass" is playing at the Talon. However, the film was released in October of 1961 and Louise McCallum was killed in June of 1961. So the flashback would be set before the film was released.
Other mistake: When Ryan gets hit by Martha's car, you can see he has both shoes on as he's going to the ground, and we never see a shoe flying through the air during the hit. Then James and Debra find the shoe in the middle of the street as they watch Martha drive off.
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)
Other mistake: When he takes Lana to the Fortress of Solitude, Clark squeezes a rock and when he opens his hand we see a perfectly cut diamond. Problem here is that in the real world, diamonds don't come out of the earth already cut and shaped. (00:04:20)
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