Re: Kryptonite in first film... Extent of use?
Green Kryptonite is the only substance that can kill Superman, but there are many ways to defeat(neutralize) him, and the rare nature of the element on Earth should make those alternative methods more prevelant.
As far as including it in the first film......no...particularly if Zod is the villian.
"No comment, until the time limit is up."