Glyphosate is an analogue of the amino acid glycine. It works by interfering with the shikimate pathway – a seven-step process used by plants, bacteria (including our gut bacteria), archaea, fungi and some protozoa to synthesise folates and amino acids. Specifically, glyphosate inhibits an enzyme called EPSP synthase (5-enolpyruvylshikimate-3-phosphate synthase) which is required to produce the amino acids tryptophan, tyrosine and phenylalanine – all of which are needed for plants to grow.
Humans depend on the shikimate pathway working in our gut bacteria as well as in plants to supply us with essential amino acids. Glyphosate is absorbed by the foliage of plants and to a lesser extent the roots, so it cannot be used to prevent germination of a plant, only once the plant has started growing. Once the EPSP enzyme is inhibited, shikimate builds up in the plant, diverting resources from where it is needed and causing the plant to turn yellow and die.
Glyphosate was first discovered by a Swiss chemist in 1950. It was developed and brought to market in the 1970s by multinational agrochemical and biotech giant Monsanto (recently acquired by pharmaceutical company Bayer), under the name of Roundup®. Monsanto’s marketing tagline for Roundup was “a herbicide that gets to the root of the problem.”
Since the seventies, its use has grown by over 100-fold, making it the world’s most used herbicide, in part due to the rise in glyphosate-resistance amongst plants. There are now several hundred different glyphosate products on the market.
Monsanto has developed a number of genetically modified crops that are resistant to glyphosate, so that farmers can broadly apply the herbicide to their crops. As we will discuss later, this affects far more than just the crop. Glyphosate resistant crops include soy, cotton, canola, beets, sugar cane, alfalfa and maize. Currently, over 90 percent of U.S. corn, upland cotton, and soybeans are produced using genetically engineered varieties.
Ignoring Gut Bacteria: The Great Shikimate Debate
The human health impacts of glyphosate exposure is a heated topic. This is unsurprising considering Roundup delivered a whopping $4.8 billion in revenue to Monsanto in 2015. There are significant financial interests in suppressing comprehensive research into this topic. Companies like Monsanto argue that Roundup® cannot be toxic to humans because we do not have a shikimate pathway. However the bacteria in our guts do.
Glyphosate also disrupts methionine, an essential sulfur-containing amino acid, and glycine. Numerous other vital molecules including serotonin, melatonin, melanin, epinephrine, dopamine, thyroid hormone, folate, coenzyme Q10, vitamin K, and vitamin E, depend on the shikimate pathway metabolites as precursors. As such, glyphosate’s disruption of the shikimate pathway very likely affects our health, contrary to Monsanto’s assertions.
Glyphosate and Cancer
In 2015, the World Health Organization’s International Association for Research on Cancer identified glyphosate as a “probable carcinogen” whilst in the same year the European Food Safety Authority stated that glyphosate is unlikely to cause cancer, words that were echoed by the US Environmental Protection Agency (EPA) in 2018.
Although glyphosate is regularly found in human urine (both from those experiencing direct exposure and via food), there is no consensus on what a safe tolerable daily intake is. The US EPA sets a limit of 1.75mg per kilogram of body weight whilst the EU’s limit is much lower at 0.3mg per kilogram of body weight. Glyphosate residues in food are found up to a year after the herbicide’s application.
Despite this disagreement, there are a number of studies indicating glyphosate exposure is toxic to humans and animals. To this end, Bayer has been forced to payout almost $11 billion in the settlement of 95,000 non-Hodgkin lymphoma and cancer claims from sufferers linking their illness to RoundUp exposure.
In 2015, after reviewing approximately one thousand published studies on glyphosate, a working group of 17 World Health Organization experts from 11 countries deemed glyphosate a category 2a carcinogen. That means it is likely to cause cancer in humans and that there is sufficient evidence of its carcinogenic effects in animals. The WHO scientists also concluded there was strong evidence that glyphosate damages genes, causing mutations.
In 2019, the Agency for Toxic Substances and Disease Registry (part of the US Department of Health) released its draft toxicology report on glyphosate concurring and even strengthening the WHO’s findings. This was despite efforts from Monsanto, working in collaboration with the US EPA’s Pesticide Office, to suppress the report. In fact, US EPA’s Pesticide Official Jess Rowland was caught telling Monsanto’s Dan Jenkins, “If I can kill this I should get a medal”.
Glyphosate Linked to Neurodevelopmental and Neurodegenerative Disorders
In addition to demonstrating statistically significant links between glyphosate and cancer in humans, the ATSDR report also links glyphosate with developmental delays, gastrointestinal effects including nausea and vomiting, kidney and liver toxicity, and eye irritation in rodent and some human studies.
The ATSDR highlighted a link between parental use of glyphosate among farm families and an increased risk of neural tube defects, miscarriage, preterm delivery, and small for gestational age (ATSDR Table 2-5, p. 40-41). Animal studies of early life exposure to glyphosate indicate an increased incidence of testicular lesions, elevated abnormal sperm, decreased testosterone, decreased sperm production, and skeletal malformations (ATSDR, p. 14). Long term studies by the US National Cancer Institute link glyphosate exposure to chronic bronchitis, wheezing and asthma (ATSDR, Table 2-5, p. 36; Ag Health Study).
Recent research has suggested a link between glyphosate and neurodegenerative disease, such as Parkinson’s, and prion diseases. This is thought to be due to glyphosate’s disruption of bile acid homeostasis, which causes a toxic buildup of manganese in the brain.
Laboratory studies have found evidence that glyphosate may contribute to endocrine disruption in animals and human cell lines, even when used at concentrations below those applied in agriculture. Ironically, chemicals that act as endocrine disruptors often have an inverted-dose effect, whereby low doses can cause more acute effects than high doses. Considering many of the published studies on glyphosate look at high dose effects, one might infer that they have missed the full picture.
Interestingly, the adjuvants in pesticides inflate the toxicity of the active ingredient. A 2014 study showed that Roundup® was 150 times more toxic than glyphosate on its own, stating:
Despite its relatively benign reputation, Roundup® was among the most toxic herbicides and insecticides tested.
Systemic Effects of Glyphosate
Whilst glyphosate is used to control weeds, its effects on our environment are clearly far more systemic than that. Other plants, animals, insects and surrounding ecosystems are exposed to its application in the soil, water and from run-off and precipitation. The full impact of these effects is poorly understood as toxicity studies have tended to be laboratory based, high dose and include a limited number of species – very different conditions to what is found in nature.
Once in the soil, glyphosate is rapidly degraded by microbes into aminomethylphosphonic acid (AMPA). When applied to hard surfaces (e.g. sidewalks) rather than soils, up to a quarter makes its way into the waterways through run-off. It is commonly found in soils and waterways, particularly those downstream from agricultural sites, and to a lesser extent in wetlands and groundwater.
So widespread is its use that it is found in rain (the US Geological Survey found glyphosate in 86% of rainwater samples). It persists longer in soil than in water, with a half life in soil of over 12 months in some cases, depending on the soil composition (soils with higher clay contents hold onto glyphosate for longer whereas it is washed out of sandy soils faster).
Once in the soil, glyphosate can form complexes with metal ions, which may affect the availability of soil nutrients. In fact, it has been shown to interfere with the uptake of key minerals in agricultural crops and to alter the composition of soil microorganisms, the full effects of which are poorly understood. For example, glyphosate reduces populations of fungi-suppressing microorganisms whilst reducing the growth of symbiotic fungi. Researchers find that earthworms, critical to soil health, are also adversely affected by glyphosate.
According to McGill University researchers, glyphosate can trigger biodiversity loss, which in turn affects all of us. We are already in the midst of unprecedented biodiversity loss, with over a million species at risk of extinction, according to the United Nations. The last thing we need is more damaging chemicals accelerating this process.
Non-target plants are impacted by glyphosate application. Studying the impact of glyphosate on 23 native non-target species, Argentinian researchers found that all species showed lethal or sub-lethal effects after just 25% of the recommended field application rate of glyphosate, with 50% of species exhibiting phytotoxicity or death.
The decline of the Monarch butterfly in North America has been linked to glyphosate use. Glyphosate obliterates milkweed – the plant on which Monarchs exclusively lay their eggs. By some estimates, over 850 million milkweeds have been lost since 1999 – over 70% of the plants relied upon by the Monarch butterfly. In 2019/20 alone, monarch caterpillars in Mexico plummeted by 53%. Butterflies are key indicators of ecosystem health and biodiversity, with their fragility making them quick to react to changes in the environment.
But the impacts aren’t limited to insects. Research indicates that glyphosate impacts upon the cardiovascular systems of mammals, with a 2015 French study linking abnormal heart patterns to glyphosate exposure. It has also been found to be toxic to amphibians, for example shortening the bodies of frog embryos and interfering with enzymes required for normal nervous system development in tadpoles. Toxic impacts have also been found among mussels, carp and eels, among other species.
Protecting Ourselves and the Environment
According to the United Nations Food and Agricultural Organization, we are on-track to reach over 9 billion people by 2050. How on earth do we feed a population like this? This is one of the arguments used by industrial agriculture – that we simply cannot feed the world without it and its arsenal of chemicals like Roundup®. In fact, this argument couldn’t be further from the truth.
We certainly need ways to grow more food, but we need to do it in ways that do not harm the natural resources that enable us to grow that food – which is exactly what industrial agriculture does.
Modern industrial agriculture is pumping our environment with harmful chemicals, creating monocultures and toxic waste products that are altering the natural ecosystems we depend upon. For example, food production (including post-farm processing) accounts for one quarter of all greenhouse gas emissions. Pollution from conventional agriculture (specifically the loss of nitrogen from farming in the Mississippi River Basin) is also a large contributor to the 9,000-square-mile dead zone in the Gulf of Mexico.
Organic agriculture, by comparison, can generate fewer greenhouse gas emissions, and uses less energy whilst protecting soils and sequestering carbon. Organic methods are also capable of producing competitive yields during stable weather conditions and out-producing conventional agriculture during times of drought and flooding, the latter of which we can expect a lot more of in a warming world. This is because organic soils retain more moisture, thereby producing higher yields during periods of drought.
According to a team of American scientists, organic farming could provide sufficient food for the entire human population, whilst causing less pollution and fewer health problems than conventional agriculture. Organic food has a higher nutrient content than conventionally farmed food, protecting us against illness.
When it comes to glyphosate, switching to an organic diet reduces glyphosate levels in the body significantly and rapidly. In a 2020 US study, researchers found that switching to an organic diet reduced urinary glyphosate levels by an average of 70% in just 6 days for both children and adults. But there are powerful lobbies and interests working hard to maintain the status quo, which is why organic and regenerative forms of agriculture currently make up such a small percentage of the global food supply.
To shift these numbers, all of us need to play a part. That includes lobbying our politicians to regulate companies that produce products which harm our health and environment, boycotting companies that pollute the environment and buying safer alternatives, including switching to chemical-free, organic products wherever possible. Many great schemes exist now where you can buy direct from producers to support local sustainable agriculture, cutting out the middle-man and accessing good, clean, healthy food at an affordable price.
Continuing business as usual and relying on harmful chemicals like glyphosate is not worth the loss of our health or that of our planet. Especially when there are already viable alternatives that can feed us and our world sustainably.
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 90% confidence interval rather than the 95% required threshold, though still sufficient to prompt tighter regulation to avoid the risk of harm.