Glyphosate, how you torture me

By Benjah-bmm27 (Own work) [Public domain], via Wikimedia Commons
By Benjah-bmm27 (Own work) [Public domain], via Wikimedia Commons
I’m a gardener, and spent years studying chemistry so this subject interests me. Therefore I am going to inflict it on you.

Chemicals are scary if you don’t understand them, and people especially get worried by the ones we use regularly on food plants and in horticulture, pesticides and herbicides. I want to concentrate on just one, Glyphosate; it is used in 750 different products worldwide and is the most popular herbicide in the world [1]. It’s a broad spectrum herbicide used in domestic, agricultural and forestry settings and by every council in the country to keep the paths tidy and cut the lines in to football and cricket pitches (except in Bristol, where they’ve experimented with vinegar after a successful campaign by local campaigners to ban the use of glyphosate there by the council).

In March last year an International Agency for Research on Cancer (IARC) monograph was published reviewing the safety of several organophosphate pesticides and herbicides; the conclusions drawn from it have been used to support calls to ban glyphosate by several organisations, including the Green Party.

I read the summary the committee published in The Lancet Oncology [2]. Seventeen experts from eleven countries assessed the carcinogenicity of five organophosphates. In the summary glyphosate gets the last three paragraphs of a two page summary. The IARC monographs don’t provide the results of primary research but reviews current research available. There are a set of clear rules that set out which studies can be considered in the review; they are broadly limited to peer-reviewed publications and government reports. This meant that many industry submitted studies were rejected, resulting in complaints from industry that the review was unfair[3].

Out of interest I made an initial search of the internet and found plenty of references to how safe glyphosate is. However, the IARC monograph gave it a new classification, 2A – Probably carcinogenic to humans – based on limited evidence in humans for non-Hodgekin Lymphoma, ‘sufficient’ evidence in animals, and mechanistic evidence of genotoxicity and oxidative stress. The IARC Monograph has begun to have an affect on the search results, bringing up plenty of popular reports about the dangers of glyphosate. Reading the summary, we find more details. I’ve done my best below to share them with you, as I have read it from the Lancet summary.

A long running cohort study in the US, the AHS, didn’t show a significantly increased risk of non-Hodgkin lymphoma, but in male CD-1 mice ‘glyphosate induced a positive trend in the incidence of…renal tubule carcinoma’. Other studies of mice ‘reported a positive trend for haemangiosarcoma’ [4], while in two rat studies glysophate ‘increased pancreatic islet-cell adenoma’. Glyphosate, its formulations and a breakdown product, AMPA, indiced oxidative stress in rodents.

That’s the rodent studies, as for humans glysophate was detected in the blood and urine of agricultural workers. This suggests absorption of the herbicide. In addition, a breakdown product of glyphosate, aminomethylphosphoric acid (AMPA), has been detected in blood after poisonings. Soil microbes break down glyhosate to AMPA; the detection on AMPA in blood suggests that intestinal microbes metabolise glyphosate in the body. Glysophate and glysophate formualtions induced DNA and chromosomal damage in human and animal cells in vitro, and one study ‘reported increases in blood markers of chromosomal damage…in residents of several communities after spraying of glysophate formulations’ [5].

In March 2015 the Science Media Centre[6] provided expert reaction to the conclusions of the IARC committee. Particularly questioning of the Monograph was Dr Oliver Jones, Senior Lecturer in Analytical Chemistry at RMIT University in Melbourne, who said,

The main thing in this new assessment is that two pesticides not previously assessed by the IARC (Glyphosate and Diazinon) have been reviewed and classified as ‘probably carcinogenic to humans’. Malathion has been upgraded to the same status, while Parathion and Tetrachlorvinphos are now classified as ‘possibly carcinogenic’.

This sounds scary and IARC evaluations are usually very good, but to me the evidence cited here appears a bit thin.

“The study itself says that for all compounds, the evidence of human carcinogenicity was limited or considered inadequate. Aside from this, Tetrachlorvinphos is banned in the EU anyway, while use of Diazinon and Parathion is severely restricted. Glyphosate and Malathion are quite widely used but are also extensively studied, including by the US Environmental Protection Agency which still allows their use.

“People might be interested to know that there are over 70 other things IARC also classifies as ‘probably carcinogenic’, including night shifts. In the highest category of known carcinogens are ‘alcoholic beverages’ and ‘solar radiation’ (sunlight) – along with plutonium.

“So yes, pesticides can be dangerous, but are many other common things which are also dangerous in sufficient amounts or over long periods of time –  the dose makes the poison. While absence of evidence is not evidence of absence this does seem to me to be a precautionary rather than a reactionary change.

“From a personal perspective, I am a vegetarian so I eat a lot of vegetables and I’m not worried by this report.”

Other experts concluded something similar, with added the added criticism that the IARC process doesn’t take in to account real life applications:

Prof. Alan Boobis, Professor of Biochemical Pharmacology at Imperial College London, said:

“IARC bases its conclusions on an evaluation of the human and experimental data, leading to hazard identification. They ask: is a substance carcinogenic? And if so, how good is the evidence in humans?

The IARC process is not designed to take into account how a pesticide is used in the real world – generally there is no requirement to establish a specific mode of action, nor does mode of action influence the conclusion or classification category for carcinogenicity.

“The IARC process is not a risk assessment. It determines the potential for a compound to cause cancer, but not the likelihood. Exposure assessment in epidemiological studies on the effects of pesticides is notoriously difficult. Agricultural workers, the most commonly studied group, are almost never exposed to just a single pesticide and it is very difficult to establish cause and effect.

The UK Committee on Carcinogenicity has evaluated possible links between pesticide exposure and cancer on several occasions. It has found little evidence for such a link.  At most, the evidence was inconsistent and was considered insufficient to call for regulatory action.

“These conclusions of IARC are important and should be taken into account when evaluating these pesticides, but that must also take into account how the pesticides are used in the real world. In my view this report is not a cause for undue alarm.


Prof. Sir Colin Berry, Emeritus Professor of Pathology at Queen Mary University of London, said:

“I have served on a number of regulatory bodies for the UK, EU and WHO and I am well used to sifting wheat from chaff in the analysis of pesticides. What is missing in this new assessment is balance in the consideration of the studies.

“There are over 60 genotoxicity studies on glyphosate with none showing results that should cause alarm relating to any likely human exposure. For human epidemiological studies there are 7 cohort and 14 case control studies, none of which support carcinogenicity.

“The authors have included non-Hodgkin lymphoma (NHL), but that diagnosis is no longer used in pathology because it’s far too imprecise. Even if you do include NHL there are still 7 studies, only one of which is positive – and that one is not a good study in my view.

“The weight of evidence is against carcinogenicity.

“The authors of the one study cited as ‘positive’ say the following: ‘Because 26 pesticides were evaluated for their association with NHL and its subtypes, some chance finding could have occurred. Our results showed pesticides from different chemical and functional classes were associated with an excess risk of NHL and NHL subtypes, but not all members of any single class of pesticides were associated with an elevated risk of NHL or NHL subtypes.’

“This assessment has looked at a group of 43 diseases lumped into one category, multiple pesticides with very different chemistry, and has failed to include critical data. There is nothing here to suggest that the variety of genetic changes in these diseases could be caused by these pesticides.  This appears to be a rather selective review.”

Interesting conclusions, don’t you think? These experts are arguing that the IARC review of glyphosate is flawed because the committee didn’t appear to take in to account real-life use of the compound.

Why is this important now? 

Glyphosate is up for a license review in the EU by the end of this month. It’s a big campaigning point the European Parliament Greens, who want the compound banned.

Glyphosate as a case study in science communication and environmental campaigning

Glysophate is a chemical of interest at the moment, because of the above mentioned license review. I keep getting emails from various environmental groups and campaigning organisations asking for my support in having glyphosate banned. They use the IARC Monograph conclusion, and classification of glyphosate as 2A, as their argument for banning what is a useful and popular herbicide.

In using glyphosate as our case study compound I’ve only focused on the IARC Monograph because that’s what’s being used to argue for the banning of glyphosate, but there are other studies (you can find some of them at open source journals, for example HERE). Some of these studies make a connection between glyphosate and various medical conditions in different parts of the world.

The use of any herbicide has to be carefully controlled and regulated; if handled incorrectly any herbicide can cause illness, including poisoning. Long term exposure may cause cancer or other diseases. Misuse may also cause environmental damage, and the forcing of evolution of resistant weeds.

MAY is the important word here. Remember that. One of the problems with popular coverage of science is the tendency to try to make things black or white. Often there is no room for ‘may’ or subtlety in conclusions. I think a lot of people want to hear a definitive answer to the question ‘is glyphosate safe?’

The answer, unfortunately,  is not unequivocal. That’s normal for complex compounds in complex environments, which is how herbicides and pesticides are supplied and used in the real world.

Remembering that is important when people are arguing about the use or banning of chemical compounds. As I pointed out in my opening paragraph, in one UK city a campaign to ban glyphosate has been successful. The campaign was supported by The Green Party and based on the idea that glyphosate is toxic to humans. The IARC Monograph, and it’s classification of glyphosate as 2A, is used to support the call for a ban.

In this case the IARC review has been used to support an existing agenda. That’s not a criticism, the IARC monograph is supporting evidence in the case for banning. The problem in this case is that there is competing evidence and expert opinion that disagrees with the classification. This disagreement between experts and evidence leaves non-specialists needing guidance. And they’re not getting it. Those opposed to man-made chemical pesticides and herbicides say it is unequivocally dangerous; some experts and industry researchers say it is unequivocally safe. The truth, from the evidence available, is not as simple as either group would like people to believe.

To ban or not to ban?

Don’t ask me, I’m not a toxicologist or a cancer researcher or an expert of that nature, all I do is write about this stuff.

Personally, I use glyphosate sparingly and according to the instructions to remove difficult weeds that pulling out won’t get rid of. I wear proper shoes (not sandals) and wash my hands after use. I even change my clothes after using it. Industrial use of glyphosate usually involves the wearing of disposable overalls and gloves, masks etc. People who use this stuff professionally don’t mess about with it. Given the finding that glyphosate and breakdown compounds have been found in blood and guts, according to some studies, these are sensible precautions, since we don’t know with any certainty what long-term exposure will do. Even the IARC review concludes it has limited evidence for carcinogenicity in humans.

You have to make up your own minds about the evidence, but I believe, used with sensible precautions, glyphosate is the most suitable herbicide we have. The herbicides it replaced are considered to be much more dangerous to humans and are proven to be so, rather than the ambivalent evidence presented by the IARC Monograph and classification with regards to glyphosate.





[4] WHO/FAO. Glyphosate. Pesticides residues in food 2004 Joint FAO/WHO Meeting on Pesticides Residues. Part II Toxicological. IPCS/WHO 2004; 95-162.

This link comes from the Lancet summary, I checked it myself (accessed 11/06/2016) and the page has been updates in light of the IARC Monograph.

[5] Bolognesi C, Carrasquilla G, Volpi S, Solomon KR, Marshall EJ. Biomonitoring of genotoxic risk in agricultural workers from five Colombian regions: association to occupational exposure to glyphosate. J Toxicol Environ Health A 2009; 72: 986-97.



  1. Good to see a levelheaded discussion of this. Too often, these things turn into people shouting that “all chemicals are bad” (the fact that water and oxygen are chemicals notwithstanding).

    1. I try to be as fair as possible. I’m frustrated by the tone of the conversation about herbicides, pesticides, GMO’s etc, because it’s always ‘They’re safe’ or ‘they’ll kill you’ without any nuance. Chemophobia – and it is an irrational fear – makes me wonder about the state of science education and communication in the world.

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