Continuity mistake: Chloe is sneaking around inside the warehouse that Lex is using to hide the space ship. After she is found by a security guard she turns back around to look in where the ship is. When she does a shot from her POV shows the fan blades spinning faster then they were in the shot before and after when we are looking at Chloe through the fan.
Continuity mistake: At the Daily Planet, after the opening credits, Clark tells Chloe that he found his mom unconscious in a field. He did not find her in a field, he found her in the driveway in front of the house. Later, at the hospital, Clark tells his father that he found her in the driveway.
Other mistake: Lois' car has the plate number "AJH 927." This is the same plate number that Senator Jennings had on his car in a previous episode, "Exposed."
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