You need to be concerned with both [0].

In short, nitrites and nitrous oxide do the preservative work. Nitrates convert into nitrites and later nitrous oxide over time. But nitrites can also convert into nitrosamine, which is the danger chemical.

[0]: https://www.americastestkitchen.com/cooksillustrated/article...

AFAIK one gets converted into the other by bacteria and both could react to the strongly acidic environment in the stomach and form nitrosamines which is how we think ingesting them increases chances of cancer.

Distinction without a difference. Nitrates breakdown to nitrites with the help of bacteria native in meat itself

Similar chemicals can have vastly different biological characteristics, like if one can bind to a certain nueroteceptor (or pass the blood-brain barrier in the first place) or not.

Chloride is a basic chemical used by the body. Take away an ion and make it chlorine, and it is fatal in very small quantities.