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Paracelsus' poison

Parkinson’s and glyphosate (or - what do I have to do? Rent out billboards with “it’s the dose that makes the poison” on them?)

Various groups (eg here) have been citing an article currently in press, “Glyphosate induced cell death through apoptotic and autophagic mechanisms” by Gui et al., as evidence that the herbicide [glyphosate]( is linked to Parkinson’s disease. It’s not, not by a long shot, and you know what I’m going to say next: “it’s the dose that makes the poison”.

The findings centre around what happens when you incubate a cancer cell line, PC-12 cells, with glyphosate. Now, I’m quite familiar with these cells, I use them (or rather, I cause my research students to use them), in my research into anti-Alzheimer’s drugs, and although a great fan of these cells as models I am painfully aware of their limitations.

Nerve cells are really hard to grow in tissue culture, but PC-12 cells, despite being cancer cells, are tolerably close to real nerve cells for doing things like screening drugs or basic toxicology, like the studies of Gui et al. One of the problems is that we can put concentrations of drugs on our cells in dishes that we could not hope to achieve in real people.

And thus it is in this study, the concentration at which they just achieved a toxic effect on PC-12 cells after 3 days exposure was 5 milli Molar (mM). That’s high, you would have to drink two cups of raw glyphosate* to achieve that sort of concentration in your blood plasma, and that will have you in hospital quick smart (5mM is the threshold of lethal plasma concentrations). You are certainly not going to be drinking raw glyphosate for 3 days.

The threshold concentration for lethality in PC-12 cells is around a million times higher than what people who actually spray glyphosate on crops are exposed to in their blood, let alone the sorts of concentrations consumers would be exposed to. Especially since glyphosate is rapidly broken down in the environment, and very poorly absorbed from the gut or skin.

Now, I know that chronic exposure to sub-lethal concentrations of substances may have long term risks, but this study does not point in that direction. Long term animal studies have shown no signs of Parkinson’s disease, and epidemiological studies show no significant association of glyphosate with Parkinson’s in humans.

So the results of this study which use toxic concentrations of glyphosate in PC-12 cells throw absolutely no light on any putative link between Parkinson’s and glyphosate. Yet through the wonders of the Internet the Gui et al. paper will be cited as “evidence” that glyphosate causes Parkinsonism for years to come.

  • this is assuming you are using the most popular concentrate (360 g/Litre), you weight 80 Kg, using a low estimate for volume of distribution of 2.3 Litres/Kg and you are using 250 ml cups.

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