PhD in pesticide science here (technically entomology and toxicology as co-majors), plus 20 years experience. I have never worked, nor will I, for any pesticide manufacturer.
Let's follow the "pathway to harm," or "adverse outcome pathway" if the hypothesis (that glyphosate applied to corn can survive the biofuel production process into biofuel which then survives the combusion process to be present in ambient air to where it could irritate the lungs and complicate a covid infection) is to be tested.
The biggest hurdle, and the first one I checked out, is that
according to this article glyphosate and its major metabolite AMPA have half-lives in the decimal to single-digit milliseconds at 1000 Kelvin. According to this
article (not peer reviewed), a diesel engine (in which biodiesel is burned; I don't know how many gasoline engines in the U.S. burn biofuel) runs at 2500 C (or 2773 Kelvin). In food safety circles, this is the "critical control point" at which the adverse outcome pathway ends; there is no further threat beyond this.
I could go on, however. All pesticides begin to break down the instant they are produced, and degradation accelerates significantly when the pesticide is diluted and even (for modern pesticides) faster once applied. Most formulations must be used within hours of mixing or the concentration is so degraded it's not as effective.
The Round-Up label specifies a "re-entry interval" (the time between which it is applied and when people can re-enter the field, such as to harvest, without specialized equipment) is 12 hr, which is quite short and indicates not only low acute toxicity, but rapid degradation as well. Now, because glyphosate is systemic, it is taken up by the plant and redistributed with times to 50% reduction in concentration from 2 to about 30 days (
link not peer reviewed, but this sounds right and the sources are appropriate although older). Glyphosate in row crops (with one exception: non-GMO cotton in which glyphosate can be used as a defoliant to make harvest easier. This won't work for GMO cotton resistant to glyphosate, obviously, and to my knowledge neither cotton lint nor seed are used in biofuel production) is applied early in the growing season until the crop is tall enough to no longer suffer competition from weeds. Control of the weeds is more effective when the weeds are small, too. In short, the glyphosate is applied many months before the crop is harvested. Residues at harvest should be nil, as
this peer-reviewed article indicates for grains ("below the MRL" has a specific meaning; it does not mean "below detection," and without full access on my home computer to the article I can't say what residues at grain harvest they actually found).
I won't look into the possibility of glyphosate surviving the biofuel production process. The chances of glyphosate being present in auto exhaust are so remote as to not warrant further consideration. If there is a connection between glyphosate and covid, this isn't it.
Well, it might be a big nothingburger.
