In the original books, kryptonite was lethal to both humans and Kryptonians. Green Kryptonite affected Kryptonians instantly, but it took time for humans to feel the lethal affects. But in time, green Kryptonite would kill ALL types of animal life. There were also other colors of kryptonite. I remember that one color was poisonous to plants... it think it might have been yellow. But with there being so MUCH kryptonite (or asteroid pieces) so numerous around Smallville, it should have been impossible for Clark to survive there. In fact, the kryptonite should have killed all animal life in the area. It would have been impossible for Lana to stay alive wearing the piece of kryptonite in her necklace. All the kryptonite that embedded itself inside her skin should have killed her as well. But his is going by a definition of the original story. I've actually come to love what they've done with Smallville... it really was a great reboot of Superman. I can see why the series lasted so long. I just read that Ryan James' brain tumor was most likely caused by overexposure to kryptonite.