Is there a difference between the sodium nitrite found naturally present in vegetables, and the additive?

Take a cl in college level course in organic chemistry and you will learn exactly how the sodium nitrites in lunchmeat can cause cancer. I have never heard anything about naturally occuring nitrites in vegetables - what is your source? All I know is that the sodium nitrites and sodium erythrobates found in lunchmeat are carcinogenic. They are cheap preservatives and that's why lunchmeat producers won't stop using them.