Monsanto, and its German owner Bayer, maintain that glyphosate does not pose a health risk, and government officials say that residues of glyphosate and other pesticides found in food products are almost always so low that they are not considered harmful.
But international scientists affiliated with the World Health Organization have classified glyphosate as probably carcinogenic to humans, and recent studies out of Europe have found glyphosate herbicides pose not just cancer, but other health risks.
You can find the results on Healthy Florida First
First you need to define “safe”. Nothing, and I mean nothing, is safe at any level. Water is a poison at high enough doses.
So the FDA generally looks to studies to find a “no observed adverse affect level” of exposure. Often from animal studies since you can’t ethically do since research on humans.
They then set targets at 1/100th that amount to account for uncertainty.
This isn’t a static assessment either, it’s updated as new evidence arises.