The monologue … on glyphosate

Every now and again a friend from another sector asks my view on an agriculture topic in popular culture. This is usually followed by me realising that my answer might take the form of a monologue … here’s one of them:

Photo by Martin K from FreeImages

Glyphosate is a herbicide.  It is used to kill weeds, which would otherwise lower crop yields by competing for light, water and nutrients.  Glyphosate is also used to desiccate crops in some locations (eg in Northern UK) so that they can be harvested effectively and without expensive, energy-consuming post-harvest drying.  

The public discourse around this chemical is mainly about how glyphosate – often referred to as Roundup (in which it is the active ingredient) – is linked to cancer and other human health concerns, how it’s damaging to the environment, and should be banned. I’m far from convinced.

Glyphosate’s mode of action is by inhibiting an enzyme (EPSP synthase) in a metabolic pathway found in plants, fungi and most bacteria, but not in insects, animals or humans, who excrete the compound largely un-metabolised in urine and faeces.  This is one of its strengths as a biocontrol – it works in a highly targeted way.  

Glyphosate has been classified by a “probable carcinogen” by the WHO’s IARC.  However this is controversial.  To become a hazard the dose of glyphosate has to be very high – far greater than most people experience.  Other national and international agencies – such as the European Chemicals Agency, Environmental Protection Agency (USA), Health Canada – find that at typical levels of exposure there is no evidence of a link to cancer.  

A particular concern often mentioned is around glyphosate causing Non-Hodgkin’s Lymphoma (NHL).   Proponents of this concern often refer to “case control” studies, where NHL sufferers and paired-controls are asked for retrospective recollections of exposure history (“did you eat X, did you use Y”).   Recall bias is clearly one of the challenges inherent in this type of study.

By contrast, cohort studies compare people prospectively. The Agricultural Health Study carried out in the US has followed 54,000 licenced pesticide applicators and their spouses (mostly farmers) for >20 years, many of whom use glyphosate on their farms.  Their 2018 report stated “no association was apparent between glyphosate and any solid tumours or lymphoid malignancies overall, including NHL and its subtypes”.

“Taken as a whole, my view is that the risks associated with exposure to glyphosate for humans, are pretty low….”

Taken as a whole, my view is that the risks associated with exposure to glyphosate for humans, are pretty low.  On the other hand, the case for its appropriate use as a tool in the armoury against weeds is strong.   Without glyphosate, we’d have to rely on more toxic chemicals, less effective methods and higher costs.

More toxic chemicals means much impact on non-target organisms – including the farmers themselves.  Even “natural” alternatives are not necessarily not the same as “safe” – options such as acetic acid (vinegar) and natural oils usually have higher risk of damage to skin, eyes etc.  Anecdotally, many farmers who switched to “roundup ready” crops reported a rebound in the birds and other wildlife around their farms as they cut back on the use of other herbicides toxic to invertebrates and other organisms in the food chain.   

…. “the case for its appropriate use as a tool in the armoury against weeds is strong.”  

Of course there are non-chemical methods of dealing with weeds  – hand weeding, burning or steaming weeds, hoeing.  The problem is these are all currently more costly and less effective.  The greater cost would have to be passed on to consumers (farming is a notoriously low margin business) resulting in more costly food.  Not only that, lower yields means more land must be pressed into agricultural production – reducing the amount of natural habitat available to wildlife.

Perhaps most importantly, glyphosate also enables the use of hugely environmentally beneficial no-till systems.  Key building blocks of conservation agricultural practices include avoiding soil disturbance (such as ploughing) and using cover crops to protect the soil.  These practices have major benefits for soil structure and stability, drought and flood resilience, carbon sequestration and biodiversity.  However such systems rely on methods of terminating a cover crop to allow a cash crop to grow through.  Without glyphosate, no-till systems are largely impractical. 

So why all the hoo-ha?  It’s almost certainly associated with anti-Monsanto sentiment.  Monsanto genetically modified soy, cotton and corn so that they were not susceptible to glyphosate, also sold by Monsanto as “Roundup” (in which glyphosate is the key ingredient). Weed management around the crop without impacting the crop itself therefore became much easier.   Monsanto, and “Big Ag” became the target of a moral panic tied up with fears about GM; glyphosate was part of this picture.  

In a nutshell, my take is that glyphosate is pretty safe and highly effective, and the lesser of other evils:

  • It works on plants in a highly targeted way, leaving other non-target species pretty much unaffected
  • The evidence for it causing cancer, even among farmers, is weak

It is also extremely useful, and the alternatives are worse

  • Glyphosate can have positively beneficial environmental outcomes by enabling no-till agriculture 
  • It’s cost effective – the higher cost of alternatives would have to be passed onto consumers and higher yields reduce the pressure to bring more natural land into agriculture
  • Most other herbicides have higher toxicity and greater impact on non-target organisms

Those who know me, know I don’t go in for black and white very much. In this case as pretty much always, the truth is nuanced.  Don’t go drinking glyphosate, don’t apply it to your fields willy-nilly (not least because it selects for resistance!), but also don’t throw the glyphosate baby out with the bath water.  It may not be “natural”, but it’s pretty important in producing the food we need to sustain ourselves while impacting the environment as little as possible.  


The various sources I’ve relied on to draw this perspective over time are too numerous to mention and anyway I can’t say I’ve tracked them all.  Here are some I used to fact-check as I wrote this:

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