Continuity mistake: The position of Clark's sleeve to the tourniquet change between shots. When Dr. Bryce first ties the tourniquet she does so at about an inch from the end of the sleeve. In the next shot, as Clark lies unconscious and nobody touches his sleeve, the tourniquet is tied around the sleeve and no longer on his skin. Just before Dr. Bryce sticks the needle in it's back to being an inch from his sleeve.
Continuity mistake: Just before Dr. Bryce removes the vial she unties the tourniquet and the straps are completely off of Clark's arm. In the shot of Clark after that, as Dr. Bryce looks at the vial, she unties the tourniquet again.
Continuity mistake: After Clark says "I'm not leaving." Jonathan starts to talk about the list of things Martha needed to get done. As Jonathan says this there is a camera switch. Before the switch Clark is next to the window turned toward his dad. After the switch Clark is now standing further back from the window behind Jonathan's right shoulder.
Audio problem: After the DCA shows Clark and Jonathan the metallic key, Clark says, "We need to think about mom," but his lips are not moving.
Continuity mistake: In the kitchen, Martha collapses and Clark catches her just in time. Jonathan then rushes to his wife and puts his right hand on her cheek and his left hand on Clark's shoulder. Cut to a close up of Martha as Jonathan calls her name but now he has both his hands on Martha's face.
Continuity mistake: When Martha is in the kitchen and starts having a coughing fit from the toxin, she drops the pitcher of lemonade. The pitcher lands on its side and breaks, but in the next shot, the broken base is positioned upright, sitting level on the floor, the jagged broken edges waiting to impale Martha.
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