Revealing mistake: There are times when it is quite evident that Michael Rosenbaum is voluntarily bald.
Other mistake: Throughout the series, they reuse the same footage for establishing shots of the Talon. For example, one of the shots has the Talon sign say "Silent Film Festival" with a guy holding and bouncing a basketball as they walk pass the Talon is in s02e05 and s03e11 and other episodes, including s03e10 where it's the same people but the guy is holding his jacket and further back.
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