Trivia: This episode had a strong Dukes of Hazard theme as it reunited John Schneider (Jonathan Kent) and Tom Wopat (Senator Jack Jennings) who played Bo and Luke Duke respectively in the Dukes of Hazard. This included stunt driving by Jon Schneider, and him listening to "Good Ole Boys", the DoH theme song.
Trivia: Additional references to the show "The Dukes of Hazzard"; Senator Jennings (Tom Wopat) drives a '68 Dodge Charger, similar to the '69 Charger in DoH. Jennings mentions Jonathan outrunning cops when he was younger by driving through Chickasaw County, a fictional county in DoH the Dukes often weren't allowed to enter because of their probation, and were sometimes chased by the sheriff. And Jack Jennings' name is a nod to Waylon Jennings, who wrote the DoH theme song and was the Balladeer.
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