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Unnatural Fear of Roundup – Understanding Small Numbers

If you spend time understanding the science behind Roundup and glyphosate, it’s active ingredient, you soon realize that this is a safe chemical compared to many other chemicals, even ones liberally used in the home. Why is it then that so many people fear Roundup?

Probably the biggest reason is great promotion by the anti-Roundup and anti-Monsanto crowd. That is one powerful force, that brings one misleading article after another to the attention of a lot of people.

I think that another reason for this fear is our inability to understand very small and very large numbers. A recent research study found glyphosate in natural water systems and I have seen it posted by several people as proof of a real problem that needs to be feared. If these people simply understood small numbers, they would not fear the report or Roundup.

Unnatural fear of Roundup in drinking water - Understanding small numbers

Unnatural fear of Roundup in drinking water – Understanding small numbers

Glyphosate in Our Water

A recent study (ref 1) found that 41% of the 140 ground water samples tested in Spain contained glyphosate.

The abstract title is “Determination of glyphosate in groundwater samples using an ultrasensitive immunoassay and confirmation by on-line solid-phase extraction followed by liquid chromatography coupled to tandem mass spectrometry.”

The author of the quoted reference took the data of the study and came up with this title, “Glyphosate, despite its low mobility in soils, is capable of reaching groundwater. 41% of 140 groundwater samples from Catalonia, Spain contained high levels, technically beyond the limit of quantification.” Note the “contained high levels, technically beyond the limit of quantification”

The levels are in the ng/L range – that is not high levels.

What does “technically beyond the limit of quantification” mean? It certainly does not mean the levels were too high to measure – you simply dilute the sample. And if the levels were so low they could not be detected – then they are certainly not high levels.

More gobbledygook to help convince people of the terrors of glyphosate.

They did find glyphosate in 41% of the samples. That means 59% had no glyphosate – a much more positive way to report things.

I don’t have the actual paper, only the abstract, but that is enough for this discussion. I’ll assume the work was well done, and the data is accurate.

Understanding Small Numbers

The average glyphosate in the 41% of positive samples, was 200 ng/L. A number like 200 sounds like a lot and we humans really can’t visualize a ng (nano-gram), so this seems like a lot. But how much is it?

200 ng/L = 0.000,000,2 g/L

You might know that a gram is about the weight of a paperclip, but that does not really help to understand this number because it is so small.

“The EPA Allowable Daily Intake (ADI) for glyphosate is set at 1,750 µg (1.75 mg) per kg of body weight. The EU ADI is just 0.3 mg per kg body weight.” (ref 2). I’ll go with an average of 1mg/Kg.

The daily safe intake for someone weighing 70 Kg (150 pounds) is 70 mg. If you were drinking the average contaminated water in Spain you would need to drink 350,000 L before you would reach this safe level. Or putting it in terms everyone understands – 1,000,000 bottles of good Canadian beer. And that is the daily allowance.

What About The Water?

The above calculation is informative, but I left out one very important detail. Water is also toxic. I found an MSDS (material safety data sheet) (ref 3) showing an LD50 of >90 mL/Kg for water.

The 70 Kg person discussed above would have a 50% chance of dying after drinking just 6.3 L of water. They would almost certainly be dead long before they could drink the 350,000 L of glyphosate-laced water from Spain.

Interesting, probably only to a biochemist, is the fact that water would never kill you. By drinking water your body would get its sodium/potassium levels out of wack and that kills you. The water itself is not toxic.


  1. Glyphosate is capable of reaching groundwater;
  2. Glyphosate Levels in Breakfast Foods: What is safe?;
  3. MSDS for Water;
  4.  Photo Source; Aqua Mechanical (photo modified)


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Robert Pavlis
Editor of
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

52 Responses to 'Unnatural Fear of Roundup – Understanding Small Numbers'

  1. Inger Knudsen says:

    How about calling Round-up a herbicide instead of a pesticide. Herbicide sounds a lot less threatning

    • All herbicides are pesticides.

      If using the term herbicide gives people the feeling that the chemical is less threatening – which it might – then it would do no service to use the term. Herbicides can be just as harmful as any other type of pesticide, or less harmful. Each chemical needs to be evaluated as a stand-a-lone item.

  2. Kishka says:

    The overuse of glyphosate is entirely due to GMO. Since the implementation of round-up ready crops (soybean, corn, cotton, etc) all GMO, the use of glyphosate has increased world wide.

    • No it is not. Roundup was one of the most commonly used pesticides before GMO crops came on the market. Since 1990 Roundup use has been on the rise, and roundup ready crops only came on stream in late 1990s, with corn not being used until 2,000. I have discussed the “non-link” between GMO and Roundup before in

      • Kishka says:

        Yes you are right about corn, however soybeans were the first round-up ready crops way before corn. Pay close attention to the graph in the link provided below. It does match your accounts of corn and mine for soybean. Very strong (facts) links between the introduction of GMO round-up ready crops and the use higher consumption of glyphosate…

        Education is power…

        • It is not true for wheat either. Roundup was already in use in the 1970’s with increases each year. GMO wheat was invented in the early 2,000’s,k but Monsanto never went ahead with the product. From Wiki As of 2015, no GM wheat is grown commercially, although many field tests have been conducted”.

          How can you claim the increase in Roundup is due to GMO wheat, when we are not growing it?

          • Mike Ricci says:

            I have heard that many farmers in the mid-west use Roundup on conventional wheat to help the fields ripen more evenly before combining begins. I cannot verify this. We don’t grow much wheat here in Maine, but to my knowledge, Roundup is not used on the grain crops that we are commonly grown here such as oats or winter rye.

          • A quick check on this shows that in most of the US, Roundup is not used to hasten wheat ripening. It is used in Canada due to a shorter growing season, and probably in some northern mid-west states.

            This link gives some facts on the matter.

            Only about 5% of US wheat is sprayed at harvest time.

            The amounts sprayed are extremely small. The link goes through a calculation similar to the one in my post to show that almost no Roundup ends up on the wheat. Clearly showing the importance of knowing the dose before reaching any conclusion.

            The stories about “Poisoned Wheat” is just another example of fear-mongering by the anti Roundup crowd.

          • Kishka says:

            I’m sorry I missed the point, where did I mention anything about wheat.. but since you did bring wheat into the blog… the crop proved no commercial viability. The GMO wheat failed field tests year after year, and therefore, it has nothing to do with the rise of use of glyphosate…

          • Sorry – you didn’t – you said Soybean.

  3. Roger Brook says:

    Thank you for your robust defence to the doubters in your comments column. I frequently write on my blog about the practical use of glyphosate in the garden and occasionally I get links sent to me by earnest readers who think I am misguided. Most of the links are gobbledegook and I cannot bring myself to defend myself – although I have done posts discussing issues. One of the links I was sent started with ” millions of US citizens use Roundup on their lawns”. Well really!
    Congratulations on developing such an intelligent discussion with your readers.

  4. Wayne says:

    I hope you continue with this series as many things need bunking/debunking. Does manure with residue kill plants? A common thing i read is “my soil is lifeless” or “my soil is sterile” because previous owner used x to kill weeds.

    Please please continue.

  5. Thank you Robert. Good work as usual. Two thoughts come to mind:

    I wish the rather simple principle of cost/benefit analysis was taught to every high school student in America. Or junior high student. A twelve-year-old is quite capable of grasping the concept.

    Second, it has been my decades-long experience that emotion-based thinkers can only rarely be persuaded, to any degree, by facts.

    • Agree on both points.

      I have to write about this one day, but over the years I have found that almost all arguments with two sides have one side that is looking at facts, and the other, emotion. I think fact-thinkers can more easily see both sides of an argument.

      I wish many things of value were taught in school, instead of what is currently being taught. As one example, why is studying literature so much more important than critical thinking?

  6. Michael Murray says:

    Thank you for the succinct explanation

  7. marianwhit says:

    I agree that manual labour for weeding unwanted/invasive species is better…but find someone to do that backbreaking work? Riiight. Spraying it from airplanes in large quantities seems to be leading the same direction as DDT…the miracle chemical that was overused. The DDT controversy is interesting too, Robert, hope to see you write about that, as the complete ban resulted in a lot of human deaths, and it turns out that lesser quantities give good results and it is beginning to be used again. Wasn’t marijuana an evil chemical once too? I love the numbers work you have done here, and will share. It is a far less damaging impact on an ecology (is prohibited in wetland use) than the unmitigated spread of invasive species, since any local ecology rests squarely on the shoulders of its native plants.

    • A very common problem with most peoples opinions is that they don’t evaluate the alternatives and look at the harm or benefits of them. For example, lets say we ban glyphosate – what happens? Food production goes down. Food prices go up. There is less food to feed people and fewer people can buy it. What happens? How many people starve to death because of the ban?

  8. Paul Alaback says:

    Thanks for doing this post. I agree with you that discussions of health effects of toxic chemicals in are often done without a good scientific context. Detecting the presence of a chemical is very different than documenting a concentration level that poses a health risk. All the studies I have seen show that when used properly especially for spot applications it should be quite safe to use.

  9. Mike Ricci says:

    Thank you for this article/post. My concern is with “Round Up Ready” crops which can take up the glyphosate into the plant without dying so likely has residue within it. Even so, I have yet to see any firm evidence that this is dangerous. I have always heard that glyphosate is very water soluble, but once in the soil, it attaches well and does not leach out during the process of it breaking down. Thank you for getting breaking this down and squeezing the facts out of it!

    • Round Up Ready is a different potential problem. A couple of facts. Weeds formed a resistance to glyphosate before we started using Round Up Ready crops, so the crops did not cause the problem. Secondly, for most crops it is very unlikely the Ready gene will be transferred to weeds.

      Glyphosate is absorbed by soil and held fairly tightly, but that does not mean it won’t move in soil. It also has a short half life so it degrades fairly quickly compared to other chemicals. This does not mean some of it does not make it to water ways.

      • Mike Ricci says:

        Sorry, I guess I didn’t state that very clearly. I meant that RUR crops, such as sweet corn for instance, would take up the glyphosate without dying and then end up in the ear of corn which we eat. I have no idea what the concentration would be in a case like that. I wasn’t at all thinking about transference to weeds.
        As we grow no GMO’s on our farm, we use Roundup almost exclusively in the fall for perennial weeds. We have lots of earthworms and bugs and our crop residues break down fairly quickly so I guess we have lots of microbes…….and we haven’t seen any 2 headed frogs yet either!

      • Kishka says:

        Please provide link for the resistance of weeds to round up. I have a different scenario supported by thousands of scientist that clearly state superweeds originated after the use of glyphosate.

        Link to Union of Concerned Scientist, a group almost completely funded by its science community base members…

        These superweeds now require 2-3 times the amount of glyphosate. Now as you state, weeds formed a resistance to glyphosate before the start of use of Round Up Ready crops, which defies all logic. If resistance was present in weeds defeatist to create a crop that resist glyphosate and just treat the weeds which already have resistance.

        “Secondly, for most crops it is very unlikely the Ready gene will be transferred to weeds.” Transfer of DNA is only done at the ovary level of any seed producing plant and often only for plants in the same family but usually within the same genus. Thus GMO corn genes will not be found in any dicotyledon flora. However, GMO corn DNA has been found in native species of corn (huge problem there).

        Finally, “It also has a short half life” does not mean it vanishes quickly. If you start with 100 and it has a half life of a month it means only half will degrade in a month so you end up with 50. Half of the next 50 will degrade in the next month and so on. Degradation not so quick now…

        • Not sure why you write all this? The post has nothing to do with weeds.

          I agree Roundup has resulted in Roundup resistant weeds – nobody disputes that fact.

          Since Roundup was used before GMO crops were introduced, it can certainly produce Roundup resistant weeds. None of this has anything to do with GMO crops.

          Re:” “It also has a short half life” does not mean it vanishes quickly.” – actually it does mean this – A chemical with a short half life vanishes faster than one with a long half life.

          • The criticism by some concerning weeds developing resistance to Roundup is in itself a good example of how the public (not trained in chemical and biological sciences) fail to understand the broad context. That weeds developed a resistance to Roundup is not unique, nor is it alarming, disastrous, or even unexpected. Over time, organisms develop resistance to chemicals, both synthetic and organic, as well as resistance to naturally occurring pathogens and diseases. One of the main motivators of the synthetic chemical industry was the fact that by the 1950s, insects had developed resistance to the lead arsenate (organic) widely used to control the devastation of food crops, particularly the Florida citrus industry, by these insects. The human body is a prime example of organisms developing resistance to pathogens over thousands of years. In agriculture, scientists do not become alarmed when insects and fungal diseases adapt to their environment, they plan for it and work to stay several steps ahead.

  10. Sue Kusch says:

    Disappointed to see you pronounce the use of a nerve toxin as safe. Didn’t Monsanto once tell us that the toxin magically disappears after 10 days? Now we know it is in most of our water supplies and stores in our body and mother’s breast milk.

    The bigger issue here is why do homeowners need to use a toxin- because they are too lazy to weed? Because they must have perfection? Because they don’t want to support native pollinators and honey bees?

    I understand using it for highly invasive weeds that threaten entire ecosystems. But on lawns? On fields of food destined to feed humans? On soil that is filled with a rich biome? There are far better ways to serve our landscapes and our co-species.

    And your take on science is a bit skewed: reading an abstract without understanding the methodology and all findings and pronouncing a toxic chemical as safe is reckless and dangerous.

    • You should really spend some time to get the facts right.
      1) glyphosate is not a nerve toxin.
      2) I am quite sure Monsanto did not say “toxin magically disappears after 10 days” – a chemist would never say that. If they used 10 days, then would have said it has a half life of 10 days – which is a completely different statement. Where is your reference that they said 10 days?
      3) People do not use glyphosate on lawns because it kills the grass.
      4) There would be no reason to spray it on soils.
      5) Since I accepted the data in the abstract, there is no reason to read the whole paper. If I had critiqued or criticized the results I would have needed to read the whole thing. I also never said the data was correct – I simply accepted it for discussion.
      6) I never ” pronouncing a toxic chemical as safe”, at least not in this post. I simply illustrated what the data is telling us. I used the opinion of the EPA and EU for the calculations – not my own opinion.

      You, like so many other people who blindly believe Roundup is the devil, continually fail to read the information in front of you.

  11. Susan says:

    I use Roundup sparingly on invasive plants in my area. If you are not on the ban bandwagon you will be villified on online garden groups. Many of the responses are based on emotions and not on data. Its nice to have someone with a science degree weed through the misinformation.

  12. Michael says:

    Thank you for the article. I appreciate you taking the time to do these. Very well done and informative.

  13. Larry says:

    Thanks for a much needed article.

  14. Don McCatty says:

    I appreciate your science based analysis. BUT, your use of the phrase “anti-roundup, anti -Monsanto crowd. . . . one powerful source” seems to suggest a political bias on your part.
    -Don McCatty
    Royal Oak, MI

  15. sadietruffle says:

    When you consider how widely used these chemicals , the results are not concentrated . There have been numerous scientific studies for many years about the harmful effects of these chemicals. IT may not be so bad if just a few people on the planet were using them , but that isn’t the case. IN fact , where I live in Oregon , a health warning was issued this summer discouraging people from swimming , fishing and letting their dogs swim in the river because of the high levels of glosphates found in the water from run off and other factors.

    • And those studies have found very few if any harmful effects.

      Just because there is a health warning does not mean there is a health issue. Politicians do what the public wants, not what the science shows them. But I would like to see a reference to the closure information if it contains the levels found. I’ll bet they are extremely small.

  16. phanmo says:

    I’d share this post but, as a Canadian living in France, I’d probably be kicked out of the country.

    I have, however, stocked up on glyphosate!

  17. Lynne says:

    Good job!

  18. Alan Carter says:

    I think there are lots of legitimate concerns surrounding Roundup, including the domination of our agricultural systems and regulatory capture by an ever shrinking handful of companies, the effects of spraying ‘lab-safe’ compounds at landscape levels and, possibly, health effects on people who apply Roundup under actual rather than ideal field conditions. As a result folk are uncritically receptive to studies like the one you’ve dissected which sound like they might show harm in a more viscerally understandable way (‘it’s everywhere and it’ll give you cancer’). My fear is that the demonisation of Roundup means we’ll go after the wrong target. If we carry on as usual with industrial agriculture but simply slot another compound into the place of Roundup then matters will certainly not improve and might be worse.

    • 1) re:”spraying ‘lab-safe’ compounds”. Glyphosate has been field tested for many years. A recent study of works who are exposed daily to the chemical found no health risks. We are well beyond lab safe.
      2) Glyphosate has been off patent for many years and is now made by a dozen or so companies. So we have an expanding group of companies – not a shrinking one. Besides this has nothing to do with the safety of a chemical.

      The next big change in agriculture will be the development of much better plants that produce the pesticides internally. A whole new set of potential problems, but a huge potential for mankind.

      • Alan Carter says:

        I guess I didn’t make myself clear enough. I was agreeing with you that many people wildly over interpret and misinterpret findings about glyphosate. I spend quite a bit of time pointing out in my own circles that various studies held up to prove that it is the root of all evil do no such thing, and often that the ‘safe’ alternatives being proposed (salt, paraffin!) are far more harmful.

        However I also think it is important to understand why otherwise rational people act this way concerning glyphosate, and I do think that it is because it is acting as a lightning rod for wider (and legitimate) concerns about the agriculture industry. As you say, many of these concerns have nothing to do with the safety of a single herbicide, but that was my point.

        I think glyphosate has become the centre of this attention as the poster child of Monsanto. It may be out of patent (as I am aware, having used various herbicides in my job), but Monsanto’s attempts to keep control of it through licensing of Roundup Ready seeds have only made it more closely associated with them.

        The point about landscape-level dosing with pesticides is not my own, but was recently made by the UK’s top science advisor on the subject in Science (the journal). Hardly the anti-Monsanto crowd. You can read it at

        Incidentally, plants that produce pesticides in their own tissues have been availabe for many years, such as Bt cotton. The same effect had been achieved by seed coatings with neonicotinoids – on the verge of being banned in Europe outside greenhouses due to a huge weight of evidence that they damage pollinator populations.

        • It is an interesting question – why are some people so against glyphosate? I think a lot of it has to do with a lack of understanding of basic chemistry and science. In their minds all chemicals are bad. Concepts like the importance of dose and correlation are not understood. Add to this the extensive source of misinformation through the internet – any fool can be an expert. Unfortunately, the groups against glyphosate are much better at promoting their position, both in quality of reports and in quantity. It really comes down to marketing – which group is the better marketer?

          Then we have the big movement against any type of establishment which is ready to eat up any info about the evils of big business. Don’t people understand that most jobs are directly or indirectly dependent on big business?

          Re: “plants that produce pesticides in their own tissues have been availabe for many years” – actually millions of years – it is the only way plants don’t get eaten. But I do understand your point about Bt cotton.

  19. I’m certainly one that takes an evidence based approach towards Roundup (and GMOs) and I’ve used Roundup myself to fight weeds. It’s pretty clear that it’s safe.

    But I do have concerns about overuse leading to Roundup resistant weeds, much in the same way overuse of antibiotics have led to antibiotic resistant bacteria. Has anyone looked at whether or not this is happening?

    • It is definitely happening and is a large potential problem. But it is not due to GMOs.

    • Paul Alaback says:

      These are very important questions. It is well known that weeds can evolve resistance to herbicides quite quickly if they are exposed to high doses of herbicides. There is some evidence of weeds becoming resistant to roundup where it has been used the most heavily, this is why there is so much interest in finding alternatives such as Dicamba (which has many other problems). Here for example is a summary published in the Journal Weed Science in 2012 of the problems with weed resistence to herbicides

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