What’s all the fuss about glyphosate?

Glyphosate, the key ingredient in Monsanto’s weedkiller Roundup, has been in the news recently. A few weeks ago it was widely reported that a UN/WHO study had shown it was ‘unlikely to pose a carcinogenic risk to humans‘. But it then emerged that the chairman of the UN’s joint meeting on pesticide residues (who, incidentally, has the fabulous name of Professor Boobis) also runs the International Life Science Institute (ILSI). Which had received a $500,000 donation from Monsanto, and $528,500 from an industry group which represents Monsanto among others.

And then it transpired that there was going to be an EU relicensing vote on glyphosate two days after the (since postponed) UN/WHO report was released, which resulted in another outcry.

Glyphosate molecule

A molecule of glyphosate

So what is glyphosate, and why all the fuss?

It was first synthesized in 1950 by Swiss chemist Henry Martin. It was later, independently, discovered at Monsanto. Chemists there were looking at water-softening agents, and found that some of them also killed certain plants. A chemist called John E. Franz was asked to investigate further, and he went on to discover glyphosate. He famously received $5 for the patent.

Chemically, glyphosate is a fairly simple molecule. It’s similar in structure to amino acids, the building blocks of all proteins, in that it contains a carboxylic acid group (the COOH on the far right) and an amine group (the NH in the middle). In fact, glyphosate is most similar to the smallest of all amino acids, glycine. Where it deviates is the phosphonic group (PO(OH2)) on the left. This makes it a (deep breath) aminophosphonic analogue of glycine. Try saying that when you’ve had a couple of beers.

As is usually the way in chemistry, changing (or indeed adding) a few atoms makes a dramatic difference to the way the molecule interacts with living systems. While glycine is more or less harmless, and is in fact a key component of proteins, glyphosate is a herbicide.

This probably bears stressing. It’s a herbicide. Not an insecticide. A herbicide.

Crop spraying

Glyphosate is a herbicide, not an insecticide.

I say this because people often conflate the two – after all, they’re both chemicals you spray on plants, right? – but they are rather different beasts. Insecticides, as the name suggests, are designed to kill insects. The potential problem being that other things eat those creatures, and if we’re not careful, the insecticide can end up in places it wasn’t expected to end up, and do things it wasn’t expected to do. This famously happened with DDT, a very effective pesticide which unfortunately also had catastrophic effects on certain predatory birds when they ate the animals that had eaten the slightly smaller animals which had eaten the insects that had eaten the other insects (and so on) that had been exposed to the DDT.

Herbicides, on the other hand, kill plants. Specifically, weeds. They’re designed to work on the biological systems in plants, not animals. Often, they have no place to bind in animals and so are simply excreted in urine and faeces, unchanged. Also, since plants aren’t generally known for getting up and wandering away from the field in which they’re growing, herbicide sprays tend to stay more or less where they’re put (unless there’s contamination of waterways, but this can – and should, if the correct procedures are followed – be fairly easily avoided).

Nicotine pesticide

Nicotine is an effective insecticide. It’s also extremely toxic.

Now this is not to say we should be careless with herbicides, or that they’re entirely harmless to humans and other animal species, but we can cautiously say that, in general, they’re rather less harmful than insecticides. In fact, glyphosate in particular is less harmful than a lot of everyday substances. If we simply look at LD50 values (the amount of chemical needed to provide a lethal dose to half of a test population), glyphosate has an LD50 of 4900 mg/kg whereas, for comparison, table salt has an LD50 of 3000. Paracetamol (acetaminophen) has an LD50 of 338, and nicotine (a very effective insecticide, as well as being the active ingredient in cigarettes) has an LD50 of just 9.

Of course, there’s more to toxicity than just killing things, and that’s where it gets tricky. Yes, it might take more than a third of a kilo to kill you outright, but could a smaller amount, particularly over an extended period of time, have more subtle health effects?

But before we go any further down that rabbit hole, let’s take a look at that ‘smaller amount’. Certain campaigners (they always seem to have some sort of stake in the huge business that is organic food, ahem) would have us believe that food crops are ‘drenched’ in glyphosate, and that consumers are eating significant quantities of it every day.

Here’s a great graphic, made by Sarah Shultz of the Nurse Loves Farmer blog (reproduced with her kind permission), that answers this question nice and succinctly:

How much glyphosate?

How much glyphosate is sprayed on crops? (Reproduced with permission of Sarah Shultz)

It’s about 1 can of soda’s worth per acre. Or, if you find an acre hard to visualise, roughly ten drops for every one hundred square feet – the size of a smallish bedroom.

In other words, not a lot. It’s also worth remembering that although there is some pre-harvest spraying – particularly of wheat crops – no farmer is spraying their crops five minutes before harvest. What would be the point of that? Farmers have margins, just like any other business, and chemicals cost money. If you’re going to use them, you use them in the most efficient way you can. The point of spraying pre-harvest is to kill any weeds that might be present so that they don’t get into your harvest. This takes time to happen, so it’s done seven to fourteen days before harvesting takes place. It’s also carefully timed in the growing cycle. Once wheat turns yellow, it’s effectively dead – it’s neither photosynthesising nor transporting nutrients – so if it’s sprayed at this point, glyphosate isn’t moved from the plant into the grain of the wheat. Which means it doesn’t make it into your food.

The long and short of all this is that if there IS any glyphosate in food crops, it’s in the parts per billion range. So is that likely to be harmful?

In March 2015 the International Agency for Research on Cancer (IARC) – the cancer-research arm of the World Health Organisation – announced that glyphosate was ‘probably carcinogenic to humans’, or category 2A. It needs to be pointed out that this outcome was controversial, as this post by The Risk Monger explains. But even that controversy aside, lots of things fall into category 2A, for example smoke from wood-burning fires, red meat, and even shift work. The IARC did note that the evidence mainly involved small studies and concerned people that worked with glyphosate, not the general public, and that recommendations were partly influenced by the results of animal studies (really, go and read that Risk Monger post). The one large-cohort study, following thousands of farmers, found no increased risk.

And by the way, alcohol has been classified as a Group 1 carcinogen, meaning it’s definitely known to cause cancer in humans. If you’re worried about glyphosate in wine and beer, I respectfully suggest you have your priorities the wrong way round.

So, the tiny traces of glyphosate that might be on food definitely aren’t going to poison you or give you cancer. Are there any other health effects?

Gut bacteria

Glyphosate isn’t interfering with your gut bacteria (image: microbeworld.org)

One thing that the health campaigners like to talk about is gut health. Their logic, such as it is, follows that glyphosate passes though our body largely unchanged. Now, you might imagine this would be a good thing, but according to these particular corners of the internet, it’s exactly the opposite. Glyphosate is known to be anti-microbial, and since it’s not changed as it passes through the body, the argument goes that it gets into our guts and starts wiping out the microbes in our digestive system, which have been increasingly linked to a number of important health conditions.

It sort of makes sense, but does it have any basis in fact? Although glyphosate can act as an antimicrobial in fairly large quantities in a petri dish in a laboratory, it doesn’t have a significant effect in the parts per billion quantities that might make their way to your gut from food. Glyphosate prevents bacteria from synthesising certain essential amino acids (it does the same thing to plants; that’s basically how it works) but in the gut these bacteria aren’t generally synthesising those amino acids, because they don’t need to. The amino acids are already there in fairly large quantities; bacteria don’t waste energy making something that’s readily available. In short, glyphosate stops bacteria doing something they weren’t doing anyway. So no, no real basis in fact.

I have so far avoided mentioning GMOs, or genetically-modified organisms. “GMO” often gets muttered in the same breath as glyphosate because certain crops have been modified to resist glyphosate. If they weren’t, it would damage them, too. So the argument goes that more glyphosate is used on those crops, and if you eat them, you’ll be exposed to more of it. But, as I said earlier, farmers don’t throw chemicals around for fun. It costs them money. Plus, not-really-surprisingly-if-you-think-about-it, farmers are usually quite environmentally-conscious. After all their livelihood relies on it! Most of them use multiple, non-chemical methods to control weeds, and then just add the smallest amount of herbicide they can possibly get away with to manage the last few stragglers.

Ah, but even a little bit is too much, you say? Why not eat organic food? Then there will be absolutely no nasty chemicals at all. Well, except for the herbicides that are approved for use in organic farming, and all the other approved chemicals, famously copper sulfate and elemental sulfur, both of which are considerably more toxic than glyphosate by anyone’s measure. And, of course, organic food is much more expensive, and simply not a feasible way of feeding over seven billion people. Perhaps, instead of giving farmers a hard time over ‘intensive’ farming, we should be supporting a mixture of sustainable methods with a little bit of, safe, chemical help where necessary?

In summary, the evidence suggests that glyphosate is pretty safe. Consuming the tiny traces that might be present in food is not going to give you cancer, won’t cause some sort of mysterious ‘leaky gut’ and it’s definitely not to poison you. There is a lot of fuss about glyphosate, but it’s really not warranted. Have another slice of toast.

EDIT 2nd June 2016

After I wrote this post, a very interesting article came my way…

  • Petaluma city suspended use of glyphosate in favour of alternatives. Notable quote:“Having used the alternative herbicides over the past two months, DeNicola said crews have needed to apply the treatments more often to achieve similar results. The plants are also likely to regrow, since the root remains alive underground.The treatments are also said to be extremely pungent during application, with several workers complaining of eye irritation and one experiencing respiratory problems, DeNicola said. Those attributes have required the use of new protective equipment, something that was not required with Roundup.“It’s frustrating being out there using something labeled as organic, but you have to be out there in a bodysuit and a respirator,” he said.”

A classic example of almost-certainly unfounded fear leading to bad decision-making.

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30 thoughts on “What’s all the fuss about glyphosate?

  1. An interesting post on an emotive topic. I’m currently reading The World According to Monsanto by Marie-Monique Robin and have just started reading about glyphosate, so very timely.

    Given Monsanto’s track record (PCBs, Agent Orange etc), the only criticism I would make of your article is that you haven’t really queried the LD50 value at all. The infographic is excellent but doesn’t really address the problem of persistence, and doesn’t consider what the minimum dose harmful to other organisms is. If glyphosate really is benign to animal life, why can’t you use it without wearing gloves?


    • Firstly, I’d argue that wearing gloves isn’t an indicator of toxicity. Gloves are a standard, pretty basic precaution. Even if whatever you’re handling isn’t toxic, you might wear gloves purely to protect your skin. Lots of people wear gloves to do the washing up; we don’t infer from that that dish detergent is lethal. Glyphosate has been tested and hasn’t been shown to irritate skin, but it is known to be an eye irritant, so gloves and eye protection are a sensible precaution.

      Secondly, my post didn’t say glyphosate was totally benign to animal life. The IARC’s categorisation of glyphosate as a 2A carcinogen was partly based on the results of animal studies. However, glyphosate binds strongly to soil, and since it’s a herbicide (not an insecticide) it doesn’t ‘travel’ much. Once it’s in the soil it’s broken down pretty quickly by microbes. Most of the evidence demonstrating toxicity is based on very heavy consumption, nothing like the quantities that are actually used in practice. There are lots of links and references here: http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html

      Finally, I think it’s worth bearing in mind that Marie-Monique Robin is a journalist, not a scientist. She’s made her living out of writing sensationalist things; that’s what journalists do. People are far less interested in paying for books and articles that say “it’s not that exciting, really”. I haven’t read her book and I’m not going to critique something I haven’t read, BUT if I were reading it I’d have a sharp eye open for cherry-picking data. The one study that appears to show something terribly dramatic is a lot more exciting than the fifteen other studies that show no such result.


      • Fair points. That said, gloves are used for a variety of reasons, so I think that your comparison with washing up liquid is slightly disingenuous.
        Also, you shouldn’t dismiss the one dramatically different study, just because it is different. It is the quality of the respective research that needs to be considered.

        The other issue that needs to be taken into account is context. Laboratory is different to field and one field is different to another. Glyphosphate does break down, but the rate varies and there is a danger of contaminating water courses.
        If we want plentiful food then we do need to do things to protect crops and increase yield, but this does need some care and consideration. There are lots of examples of things that seemed like a good idea at the time but have been shown to have longer term implications.


      • Firstly, not to get into an irrelevant debate about gloves, but with respect you started it when you said: “If glyphosate really is benign to animal life, why can’t you use it without wearing gloves?” Like you’ve just commented, gloves are used for a variety of reasons, so that was a bit of a fallacious statement. Secondly, I’m not saying studies that show a different result should be dismissed. I AM saying that choosing to report ONLY that study, ignoring all the others with a different (usually less interesting) result, is cherry-picking, and something everyone should be alert to. Finally, yes, we should be alert for potential problems with glyphosate (and any other agricultural chemical), but the point is that people HAVE been looking. They’ve been looking really, really hard. And so far, there’s precious little to see.


      • Thanks for taking the time to continue the discussion – I’m finding it very useful. With regard to the gloves, I think my point was that there are times when you might choose to wear gloves but don’t need to protect your hands from harsh chemicals (washing up, unless you are using something really nasty) and times when you have to. I’m finding the Robin book a bit of a slog – she has started from a particular viewpoint and is justifying this. However, she does appear to have done a lot of research to support this – I wish I had the time to check her references. From her perspective though, people have been looking hard, and have found some problems.
        Clearly there are a number of agendas in play: whilst I have enjoyed your posts on a number of topics, I don’t think you have made your case in this instance, but thank you for the timely reminder of the potential for sensationalism in the media and the need to look carefully for gaps in the evidence!

        Liked by 1 person

    • Ah yes, the old argument that Monsanto made Agent Orange. Monsanto didn’t invent it – the U.S. Army gave them the formula and Monsanto manufactured it (as actually required by the defence production act) along with Dow, Uniroyal, Diamond Shamrock, Thompson Chemical, Hercules, etc. Monsanto did not claim it was safe, and as early as 1952, they warned the Feds against using Agent Orange due to dioxin contamination. The government’s response was to ignore this data and use it anyway.

      Liked by 1 person

  2. An excellent article, putting glyphosate into its context. Of course, truth is truth, whoever pays for the research but this link (also quoted in another comment) is to a university project supported by the US government (I don’t know if that is a problem for anyone): http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html
    It seems to show that glyphosate is a lot safer than other things you might find in your food, water or the air you breathe. Toxic effects are only found in gigantic quantities.
    As Paracelsus said: the dose makes the poison.
    Tiny criticism: glycine is a component of proteins, not DNA.


  3. Oddly no one seems to mention Paraquat any more. We used to use it as GRAMOXONE with little protection. I sprayed nettles and thistles with a knapsack sprayer for some years as a teenager. Admittedly it does not kill the roots of the foliage it kills back. But our cows loved the dying thistles ( which they would not touch before spraying ) They all lived longer than many, and it seems to have done me no harm…

    Liked by 1 person

    • Blimey, have you looked it up recently? It has LD50 vales of 57 mg/kg for rats and 130 mg/kg in mice. It’s extremely dangerous when the concentrated product is being handled during preparation. It was used in 1981 by a British woman to poison and kill her husband. And as if all that wasn’t enough, exposure has been linked to Parkinson’s disease. Yikes. I’ll take glyphosate, I think…


      • Still in use though. Not made by Monsanto. I am not a Monsanto apologist but as you say, glyphosate is a damn site safer. Nowadays I have very little to do with the production side of agriculture, just the eating side. As an engineer, I have milked more cows by hand than most ‘modern’ farmers, delivered calves, lambs… (we had no electricity at all)

        Liked by 1 person

  4. As a minor point, 10 sq. ft. is 1 ft x 10 ft…a smallish bedroom might be 10 x 10, or 100 sq. ft. It doesn’t change the validity of your argument but I don’t want people to disregard the important points because of a simple math error.


  5. Thanks for the information. I’m studying this compound in my master of science degree, and you really know how to explain it.
    And I also loved your blog. Congratulations on making chemistry interesting.


  6. I am far away from going ‘all chemicals are wrong’ patch (as you said in different post, every substance is a ‘chemical’, even pure water 🙂 ). However, there were studies that did show a possible cancirogenic effect of the gluphosphate. Of course, those studies could be incorrect, however, wasn’t proven so… instead Monsanto filled a lawsuit againt adding glyphosphate to possible carcinogen list).
    So, my personal approach to glyphosphate is very cautious.
    Thalidomide was considered ‘safe’ as well for few years and its effect were much more obvious.


    • As I said in the post, the IARC did classify glyphosate as “probably carcinogenic”, based on animal studies. However as I also said, this was based on large quantities. There’s no evidence that the small amounts consumers might be exposed to are carcinogenic. And the evidence that farm workers, who might be exposed to large amounts, have increased cancer risk is very shaky. The only law suit that I know of involved California’s Proposition 65, which is a ridiculous piece of legislation anyway. It’s resulted on silly labels on all sorts of things (including electronic devices, for example – even though no one eats electronic devices) that are no risk whatsoever. I can see Monsanto’s point, as it would’ve resulted in a Proposition 65 label on ALL fruit and vegetables ever exposed to glyphosate, which would be misleading in terms of the actual risk.

      Alcohol is a known carcinogen, rated more dangerous by IARC, and with many, many studies show it definitely causes cancer. And yet millions of people drink it every day. Let’s keep some perspective.


      • The main difference between ethanol – containing beverages and glyphosphate is – we know about ethanol properties (not only cancirogenic… there are several others,). When there is an ethanol in drink, we know it.. We ought to know if there is a glyphosphate in our food.
        And seriously, the fact that there are stronger carcinogens than glyphosphate, does not mean it is not harmful…

        I dont know if it is carcinogenic, but I DO believe that we should know whenever the vegetables were grown with / without glyphosphate.

        PS. About the lawsuit, I have seen this: http://www.nytimes.com/2016/01/22/business/monsanto-sues-california-over-herbicide-classification.html?_r=0 .
        Nothing about Proposition 65… I will search more on the topic.


  7. I have lost 3 dogs from cancer and my Daughter was sprayed also, so we rang the local Councils up and they didn’t want to know. I will just say this Glyphosate is a carcinogenic and we all know this. Now please open your eyes as I live in a farming community and they spray by air and by machines. So go ahead and laugh but remember you could be next !!


  8. Pingback: The Chronicles of the Chronicle Flask: 2016 | the chronicle flask

  9. Pingback: Ready for the RoundUp? | Dirt to Dinner

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