The glyphosate debate

Glyphosate began as a failed experiment. In 1950, Swiss chemist Henri Martin first synthesised it in an attempt to develop new pharmaceuticals, but the compound showed little promise. Fast forward 75 years, and glyphosate has become one of the most widely used pesticides in the world. More of it has been applied than any other agricultural chemical, with billions of kilograms sprayed since 1974 to grow almost everything, from wheat to oranges.

Now glyphosate is at the centre of an intense debate over its impact on human health and the environment. On one side, activists and NGOs advocate for stricter regulations and, ultimately, a complete ban. On the other, most farmers argue that growing food without it would be impossible. ‘I think the biggest single disease that the arable farming industry has worldwide is dependence on herbicides, and glyphosate is the biggest,’ says Tom Allen-Stevens, an arable farmer from Oxfordshire, UK. In addition to running his own farm, Allen-Stevens has a background in agricultural journalism and has covered the glyphosate controversy in depth. While he uses glyphosate himself and notes that many of his colleagues do as well, he also expresses concern about the country’s heavy reliance on the pesticide.

Farmers use glyphosate for several reasons: it is inexpensive compared to some other herbicides, easy to apply and works relatively quickly. Introduced to the market in 1974 by Monsanto (which was acquired by Bayer in 2016), glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase). This enzyme is essential in the shikimic acid pathway for synthesising aromatic amino acids in plants, fungi and some bacteria. Since this pathway is absent in animals, including humans, glyphosate was initially considered non-toxic to them. ‘We have always been told that glyphosate is one of the safest pesticides to use, and also one of the safest pesticides for the environment,’ Allen-Stevens adds .

However, new studies and assessments have begun to suggest otherwise. Hundreds of reports, based on a wide range of samples and subjects — including urine, mice and cancer cells — are painting an increasingly complex picture of how glyphosate impacts mammals, insects and ultimately humans.

Glyphosate and human health

Any biology textbook states it clearly: the cell is the basic unit of life. It is no surprise, then, that scientists focus on this fundamental level to assess how glyphosate might harm humans. A 2005 paper appears to be among the earliest investigations into glyphosate’s direct effects on human cells. In it, scientists reported that glyphosate exposure reduced cell viability and induced DNA damage in normal human fibroblasts and human fibrosarcoma cells.

Over the past few decades, other studies have explored other effects using varying doses of glyphosate. In a 2019 study, researchers examined how glyphosate alone, as well as formulations containing glyphosate, affected human mononuclear white blood cells. They found that while glyphosate alone did not cause significant DNA damage, glyphosate-based herbicide formulations substantially induced both DNA damage and cell death.

In another study, researchers used a different type of cell (human lymphocytes) and exposed them to various glyphosate concentrations. One concentration represented the acceptable daily intake set by the European Food Safety Authority (EFSA). The team observed that glyphosate exposure increased chromosomal aberrations and micronuclei formation. Chromosomal aberrations indicate direct structural damage to chromosomes, while a rise in micronuclei reflects errors in cell division.

As glyphosate’s popularity grew over the years, governments and health agencies called on the World Health Organization (WHO) for a thorough review of the pesticide in 2015. The WHO’s International Agency for Research on Cancer (IARC) did just that and reached a conclusion that was (and remains) somewhat controversial.

Is glyphosate carcinogenic?

Following a review of around 1000 sources, the IARC classified glyphosate as ‘probably carcinogenic to humans’, putting the pesticide in the same category as eating red meat or night shift work. This decision was based on ‘sufficient’ evidence that the pesticide causes cancer in animal experiments, and ‘limited’ evidence of cancer in humans from real-world exposure. The IARC classification also highlighted ‘strong’ evidence that glyphosate is genotoxic, meaning it has the ability to damage genetic material within cells.

This report relied solely on data that is publicly available and subject to independent scientific review. Consequently, the agency didn’t consider unpublished industry-sponsored studies unless they had been made publicly accessible. In contrast, regulatory agencies such as the US Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA) often include unpublished industry studies in their assessments. This difference in methodology is one of the reasons for disagreements between agencies.

Both the EFSA and EPA’s reviews state that glyphosate is unlikely to pose a carcinogenic hazard to humans. And while there is nuance in how each report is sourced and analysed, the reality is that these conflicting conclusions have fostered an atmosphere of distrust and resistance.

‘As more and more information came out that suggested that it was a probable carcinogen, it seemed as though there was 10 times more evidence to show that it wasn’t,’ Allen-Stevens says. However, he adds that this feeling of scepticism could stem from farmers being in a bubble. ‘We are very exposed to the likes of what Bayer shows us, but I think that the majority of farmers felt that they were being fed a lot of misinformation.’

He further notes that while some farmers do not believe glyphosate is carcinogenic, others seem to choose not to believe because of the implications. ‘I think there’s a certain amount of the farming community who is just sticking their fingers in their ears going “La la la, don’t want to hear this, I can’t take the prospect that I’m not allowed to use glyphosate.”’

Yield vs health

This paradox is hard to ignore. On one hand, studies linking glyphosate to health risks are empowering thousands of sick farmers and gardeners who are taking Bayer to court. Yet, at the same time, many farming organisations and farmers staunchly defend the pesticide, actively pushing back against efforts to ban it. Farmers are reluctant to stop using glyphosate, arguing that it’s difficult, if not impossible, to achieve the same yield without it. Others, however, view the situation differently.

‘We are in the middle of a biodiversity and climate crisis that needs solving,’ says Nick Mole, policy manager at the Pesticide Action Network UK. ‘It doesn’t matter how much food we eat if there’s no one here to eat it or it is impossible to grow anything anyway.’

Agriculture relies heavily on biodiversity. Insects like bees and butterflies help pollinate crops, while soil organisms break down organic matter and improve soil structure. However, traces of glyphosate have been found to affect many areas of this complex, yet fragile ecosystem. The pesticide can alter the composition and abundance of soil microorganisms (bacteria and fungi). Research also shows that contamination is common in earthworms and can severely impact their survival, body mass, and behaviour.

‘What has caused the loss of 80% of biomass in insects over the past 30 years?,’ asked Anja Weidenmüller, a biologist from the University of Konstanz in Germany. ‘I think there’s no discussing the fact that our heavy use of agrochemicals plays an important role there.’

Glyphosate and the environment

Weidenmüller works on fundamental biological questions. She studies the inner workings of social insect colonies, particularly bumblebees, and is interested in understanding their ability to maintain homeostasis. Bumblebees rely on the warmth generated by the colony to keep their brood — the developing larvae and pupae inside the hive — at a stable temperature, typically around 30–34°C. This is crucial for the health of the colony.

Weidenmüller became interested in understanding whether glyphosate could affect the colony’s behaviour and, consequently, its brood temperature and survival. She and her team investigated this in a study where they maintained 15 bumblebee colonies in the lab, with each colony divided into two halves, separated by a wire mesh. The colonies were fed daily with pure sugar water on one side and the same amount of sugar water mixed with glyphosate on the other side. However, the researchers did not feed the bumblebees equally over time. ‘I gave them the same amount of sugar water without restrictions, but on certain days, I limited the amount available to them,’ she says.

This strategy was important to mimic natural stressors. Weidenmüller explains that most studies put bees in perfect, unnatural conditions with controlled temperatures, constant feed, and no parasites. ‘That will just lead to us overlooking effects and claiming that there’s no effect when maybe there’s a very significant one,’ she adds.

Her team used a thermal camera to record nest temperatures, which reflect the brood’s temperature. Initially, when the colonies were well-fed, they didn’t observe significant differences between the glyphosate-treated nests and the control sides. However, the effects of glyphosate became apparent when colonies faced resource limitations. ‘The colony halves that had been exposed to glyphosate were less able to maintain their temperatures at adequate levels, compared to the colonies that had not been treated with glyphosate,’ she explains.

To Weidenmüller, the case was clear: although glyphosate didn’t directly harm survival, it did impact the brood, therefore the colony, particularly when bees experienced food shortages. ‘There was no effect on survival, so, classically, we would say it doesn’t harm them, right? But then you have to take a longer look to find these sublethal effects,’ she says. ‘Sublethal behavioural effects can be really detrimental.’

Much like in human-centric studies, scientists from around the world have written and published hundreds of reports showing that glyphosate affects certain aspects of insect survivability. And it is precisely because so many studies consistently show that glyphosate isn’t as harmless as once thought that there was considerable uproar when the pesticide was approved for another decade of use in the EU.

Ten more years of glyphosate

EU regulatory bodies often review contentious substances to determine whether they remain safe for use in the bloc. Given the growing evidence questioning glyphosate’s safety, the public has been particularly vocal about the potential for a ban on the pesticide. ‘There’s this sort of pressure from the public to reduce glyphosate use,’ says Helen MetCalfe, an agricultural ecologist from Rothamsted Research, in the UK.

The EU has assessed glyphosate three times. The most recent assessment was carried out between 2019 and 2023 by EFSA and the European Chemicals Agency (ECHA). Both entities concluded that there is currently no scientific or legal justification for a ban. Therefore, the pesticide was approved for use in the EU until 15 December 2033. This means that, in general, Europeans are allowed to use glyphosate, albeit under some rules.

Depending on how each national authority legislates the issue, the pesticide can be used to kill weeds in farms, gardens and railways. Some countries like Austria have banned glyphosate for private use (in gardens, for example), whereas Germany recently prohibited its use in protected water areas, domestic gardens and allotments.

The decision to not ban glyphosate sparked mixed reactions. NGOs and activists strongly disagreed and challenged the Commission’s approval of the pesticide at the European Court of Justice in December 2024. As of the time of writing, there had been no further developments. On the other hand, farmers and pesticide companies celebrated the announcement. This comes as no surprise, as farmers are heavily reliant on glyphosate. A 2019 report covering 32 countries, including the UK, highlights just how dominant the pesticide is in European agriculture. Accounting for 33% of all herbicide sales, glyphosate is one of the region’s most widely used weed killers. It is applied to 32% of wheat fields, 25% of maize fields, and more than half (52%) of oilseed rape acreage.

But how did this happen? How did farmers become so reliant on this single product?

In addition to being cheap and easy to use, Allen-Stevens points out that there is more to the story. He explains that farmers have been encouraged to reduce both the number of pesticides they use and the amount of tillage, in order to preserve soil health and reduce carbon emissions. Tillage involves turning the soil to control weeds and pests and to prepare for seeding. The more it is done, the greater the damage to the soil. The challenge, he says, is that, in an effort to reduce tillage and the use of other pesticides, farmers gradually became reliant on glyphosate – an outcome that isn’t ideal.

‘It’s a bit like boiling frogs. We suddenly got into the situation where we realised that we are completely dependent, as an industry, on this one pesticide,’ he adds. This reliance is dangerous. There are the obvious concerns about human and environmental health, and then there’s the question of resistance.

Not a silver bullet

Earlier this year, scientists confirmed the presence of glyphosate-resistant weeds in the UK. Resistance to the pesticide has been reported globally, but this marks the first time it has been found in UK soil. Experts said that this resistance won’t immediately disrupt food production in the country, and there is little risk of it spreading rapidly across farms in the UK. Nevertheless, it serves as a reminder that glyphosate is not the silver bullet it was once thought to be, and that the industry should reduce its reliance on the pesticide. ‘I think this is, by far, the biggest threat,’ Allen-Stevens says.

Mole argues that one way to reduce reliance on glyphosate would be by restricting its use, while also providing financial support to farmers so they can explore alternative strategies to combat weeds. Ultimately, he believes that without such restrictions, business will continue as usual. ‘I was at the Oxford Real Farming Conference and I sat next to a farmer on a panel discussion and he actually said, “Look, if it’s there, we’ll use it. If it’s not there, we’ll find something else,”’ Mole explains. ‘That’s the reality of everything, it’s ease.’

There are, however, concerns about potential yield losses. A recent modelling study suggests that if glyphosate were to stop working entirely or be banned in the UK, it could result in a significant loss in farm income, primarily due to reduced crop yields and profits. That said, the results are not entirely one-sided. Glyphosate-free scenarios showed positive outcomes, including a reduction in herbicide-related environmental risks and an increase in arable plant diversity.

‘If we invest in things like soil health and biodiversity, and improving those on farms, then the benefits of that will go beyond just the environmental impacts,’ says Metcalfe, who co-authored the study.

Is the UK banning glyphosate?

Glyphosate is currently authorised for use in the UK until December 2025. What happens after that is uncertain, although Allen-Stevens believes that a ban is unlikely. ‘Do I think that the UK will stop using glyphosate before the EU does? No, I don’t think so. I think if Europe says “We’re not using glyphosate any longer”, I think it’s quite likely that the UK will toe the line and do the same,’ he adds.

Mole advocates for a ban, but he too acknowledges that it may not happen soon. ‘The truth is we don’t have a functioning pesticide regulations system in the UK yet,’ he says. ‘There’s a lack of capacity of the UK government to actually be able to do the work 28 member states used to do [before Brexit].’

Whether or not a ban is imminent, rethinking an industry so heavily reliant on a pesticide as controversial as glyphosate may be the wisest course of action. This is especially true considering the public’s discontent with the chemical. In 2017, a European citizens’ initiative gained substantial support across Europe, collecting over 1 million signatures. The petition called for a glyphosate ban, a reform of the pesticide approval process, and the establishment of EU-wide mandatory pesticide use reduction targets. ‘There are a lot of strong feelings from the public [in the UK], as there were in the rest of the EU. So this is much more a political decision than anything else,’ Mole adds.

Political decisions, especially those concerning something as divisive as glyphosate, are inherently nuanced and require input from all sides to ensure a balanced approach.

‘With every decision, whether to continue the use of glyphosate or not, or these other chemicals that are currently used, this is a process that has to be participatory, it has to involve farmers as much as biodiversity researchers,’ says Weidenmüller. ‘I would really urge decision makers to take into account the information that’s out there and how agrochemicals affect not only insects, but birds and everything else.’