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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.

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

  1. 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?

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Michael says:

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

  7. Larry says:

    Thanks for a much needed article.

  8. 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

  9. 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.

  10. 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!

  11. Lynne says:

    Good job!

  12. 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.

  13. 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?

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