I remember reading that in the late 1950's the FDA limited the amount of nitrites in meat. And also required adding ascorbic acid. The idea is that when you cook meat treated with nitrites the ascorbic acid destroys the nitrite before they have a chance to form nitrosamines.
Might be that nitrites in uncooked vegies is fine.
Not unlike how 6ppd in car tires seems safe, but when it reacts with ozone, the byproduct kills salmon.