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For the past decade, everyone has been concerned with the bees. What’s happening to them? Where are they going? What is the cause of colony c […]
Why did the researchers choose the exposure levels of 5 and 10 mg? Is it reasonable to assume that an individual honeybee could be exposed to those levels outside of the laboratory?
Those levels were chosen arbitrarily. They are close to levels that are actually sprayed on crops, not levels that would be likely to be found in the environment.
The PNAS study does not show that honey bees are harmed by glyphosate.
What they showed, is that the microbiome of bees eating pure sucrose solutions, or pure sucrose solutions containing 5 ppm glyphosate and 10 ppm glyphosate are subtly different. Are those differences important? Do those differences cause adverse effects? They have not shown that.
The levels of glyphosate they are using are extremely high. Bees would (essentially) need to feed directly off of glyphosate solutions being sprayed onto fields. There is no data showing that those levels are a ‘realistic’ exposure level.
Then they showed that when they tried to grow bacteria in 10 mM glyphosate (that is 1,690 ppm), in minimal media (media without aromatic amino acids), they observed disruption to bacteria growth (figure 4). Those levels would need direct contact with glyphosate being sprayed.
That is about 5,000 times higher than glyphosate levels actually found in honey in agricultural areas.
The typical concentration of glyphosate that is sprayed on crops for suppression of weeds, is ~1.3 ounces of the 41% concentrate in a gallon of water (128 ounces). I calculate that to be about 25 mM/L or about 4,000 ppm.
Bees would have to be drinking directly from the sprayers that are spraying the diluted glyphosate onto the crops to get 10 mM glyphosate. How realistic is that?
Even with those extremely high and unrealistic glyphosate levels, bacteria were not killed, they just grew slowly. Not surprising when they use media that doesn’t contain aromatic amino acids (the way the normal bee diet does). Is that slow growth problematic?
I find it interesting that they don’t cite this paper that looked at the effects of glyphosate in rat gut. Why not? It was out before the PNAS paper was submitted. I suspect because they are trying to generate a ‘narrative’ that glyphosate is bad for gut bacteria, and the (well done) paper on rat gut microbiomes shows that it isn’t.
They measured minimum inhibitory concentration of glyphosate, (in rich media, simulating actual gut contents) for 22 different bacteria, and found it to be between 5,000 ppm and 80,000 ppm. 5,000 ppm is higher than what is sprayed on fields to suppress weeds.
Well, there was his talk about Chinese mercantilism…
Anyway, yeah, I always end up saying “It’s not killing the bees, but I killed the wasps.” (I had a major wasp infestation earlier this year.)