Unnatural Fear of Roundup – Understanding Small Numbers

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Robert Pavlis

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.”

Microbe Science for Gardeners Book, by Robert Pavlis

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.

Building Natural Ponds book, by Robert Pavlis

“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; http://www.greenmedinfo.com/article/glyphosate-despite-its-low-mobility-soils-capable-reaching-groundwater-41-140-groundwater
  2. Glyphosate Levels in Breakfast Foods: What is safe?; http://www.anh-usa.org/glyphosate-breakfast-report/
  3. MSDS for Water; https://www.ch.ntu.edu.tw/~genchem99/msds/exp26/water.pdf
  4.  Photo Source; Aqua Mechanical (photo modified)


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Robert Pavlis

I have been gardening my whole life and have a science background. 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!

63 thoughts on “Unnatural Fear of Roundup – Understanding Small Numbers”

    • Government bans are implemented by politicians. Politicians do what people want. If they have to chose between being popular and following science – they select being popular. The general public believes glyphosate is harmful so they create bans. But …. bans and lost court cases tell us nothing about the safety of a product – it only tells us about peoples opinion. Science tells us about safety.

      I use almost no herbicides anywhere in the garden. In the veg garden, I mulch with straw, which eliminates 99% of the weeds.

      Here is an important point. On this blog I am reporting the science. Roundup is safe, but that does NOT mean I recommend that everyone use it everywhere. In general, I am against the use of chemicals except in cases where they are the only good tool. I use Roundup of my thousands of buckthorns. But I don’t use perfumes, household air fresheners and many other chemicals found in the home because they are not needed.

  1. I most certainly enjoy your work. I have long believed that much of gardening was actually a collection of superstition, wives tales and “common sense”.

    Perhaps someone might apply your vigor to the new (old) realm of sourdough baking.

    But never mind. I am, however, troubled by your apparent insistence that “the dose makes the poison” and by extension small doses can or do have little effect.

    Perhaps I missed the reference to hormones or hormone like chemicals.

    A pleasant blog on the point of trace amounts.


    • Your link starts off with a serious error – “The phrase “The dose is the poison,” carries with it the implication that if something is toxic, then less will be less toxic. And a lot less is safe.”

      That is not what people are saying. When we say the dose is the poison we are saying that you have to understand the dose and its effect, before you can reach any kind of conclusions.

      Nobody, at least nobody who understands science, believes that ” half as much is half as toxic”.

      • The saying is “the dose makes the poison,” not “the dose is the poison.” In other words, whether something is poisonous is dose-dependent.

  2. I dismissed concerns about glyphosate because I understood that its half-life was on the order of a day in open air. It decomposes to carbon dioxide and water. Recently I was asked some questions that made me reevaluate my position. First, glyphosate does not necessarily decompose in the soil. In fact, its solubility in water allows it to be flushed deeper, and in permeable soils it is plausible that it reaches ground water. Given its virtually universal use, it means that if glyphosate does not fully decompose, it is likely to be in potable water sources world-wide. If so — and not a lot of research has been done on this — then it means there are concerns. An MIT researcher, Dr. Stephanie Seneff noticed the similarity of glyphosate to glycine, the amino acid found in virtually all proteins. The difference, of course, is the presence in glyphosate of a phosphate side group. There is limited — very limited, I might add — indication that some of the glyphosate consumed by lab animals remains in them, primarily in the epiphyses, or the growing portion of long bones. Alarmingly, glyphsate has been found to inhibit spermatogenesis in test animals. If there is a connection between Roundup use and spermatogenesis inhibition, this may be why fertility in young men today is decreased and — from my perspective — why we have so many effeminate males. It is also possible that masculization of women is occurring as well. Studies to-date have involved C14 labeled glyphosate. I think radioactive labeled phosphorus in the molecule is needed. Trouble is, P-32 only has a half-life of a couple of weeks, meaning tests could only be run on very rapidly dividing tissues such as cell culures and embryos. Still, this needs to be done. If cellular damage is confirmed, then Roundup needs to be banned.

    • Re: ‘its half-life was on the order of a day in open air” – I doubt that very much – do you have a reference to support this?
      Re: ‘glyphosate does not necessarily decompose in the soil” – that is not true. It does decompose in soil, but that does not mean some might not end up in the water systems.
      Re: ‘it is likely to be in potable water sources world-wide. If so — and not a lot of research has been done on this” – actually there has been a lot of research on this. That is how we know it is not an issue.

  3. The issue of bioaccumulaton in the human body over time is raised in the breakfast foods article. This would seem to be a more serious concern than tiny doses from various foods. Have you tried to evaluate this potential problem? What are your thoughts?

    • I have not looked at it in detail. Most things are not bioaccumulated in the body. Our bodies re designed to deal with chemicals it does not want. Heavy metals are an exception and we need to be concerned about them.

    • 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.

    • 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

      • 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”. https://en.wikipedia.org/wiki/Genetically_modified_wheat

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

          • 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. https://www.huffingtonpost.com/jenny-dewey-rohrich/the-truth-about-toxic-wheat_b_6180498.html

            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.

          • 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…

  4. 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.

    • Did you not know that US citizens now use Roundup Ready grass? 🙂

      Come to think of it – I bet such a product would be very popular.

  5. 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.


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