Nitrites are heavily applied as a preservative. Not sure if that’s where the ones in saliva come from or if naturally occurring (in large amounts anyway).
From your first link, Dr. Perry's belief that glyphosate might be clastogenic is certainly interesting, but also a little weird. The proposed mechanism is that glyphosate causes oxidative damage to to DNA which causes strand breakage. This is not a subtle mechanism and I would expect evidence for it to be readily available from simple tests like the Ames test. If you have the research he's using to support this claim, I'd definitely be interested in seeing it.
At the end of the day, we're left with the same haunting question however, if glyphosate so definitely causes cancer, then why has it been so hard to figure out? Monsanto is much smaller than the tobacco companies were so it's hard for me to believe that Monsanto masterminded some global conspiracy when they were only about the size of Expedia when Monsanto were bought out. Many of the most important papers critical of glyphosate have a number of issues. The IARC monograph seemed to deliberately exclude contradictory data, including a study that one of the monograph's writers was directly involved in. Even then, the monograph wasn't particularly definitive. The oft cited metastudy that came out in 2019 seemed like a big deal, but on closer inspection, they had decided that out of nearly 40 years of research, they would only examine 7 papers. Not to mention they also relied on data from exposure levels far in excess of directions provided by Monsanto.
The strongest conclusions we have about glyphosate seem to be that for exposure levels 10-100 times recommended by major health organizations and Monsanto there may be an increased chance of some cancers, though the effect doesn't seem to be large. This conclusion can get funky because some data (the IARC panel was criticized heavily for this) suggest that past a certain point, higher levels of glyphosate correlate with lower cancer rates.
>>An email by Michael Cunningham (Monsanto) to several other colleagues found them discussing N-nitrosoglyphosate (“NNG”), a known carcinogen, that can be formed as reaction between glyphosate and nitrites, which are found in many foods. Specifically, Cunningham quoted Dr. Ruth Shearer from 1984: “The problem with glyphosate… is that it combines readily with nitrites, found in normal human saliva, to form an N-nitroso compound called Nnitrosoglyphosate. Although that particular compound has not been tested as a cancer-causing agent, over 75% of all other N-nitroso compounds so tested have been shown to cause cancer by way of tumour formation.”
https://jameslyonsweiler.com/2018/08/27/dewayne-johnson-vs-m...
https://www.science.gov/topicpages/c/carcinogenic+n-nitroso+...
Regardless of whether glyphosate and nitrite can interact to form a carcinogen, I suspect we often miss potentially dangerous chemical interactions because of the way we test things.