Glyphosate

• 1. Introduction

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  Glyphosate is a weed killer. In 2010 a researcher named Powles called it "a one in a 100-year discovery." He added that it was "as important for reliable global food production as penicillin is for battling disease." From the late 1970s to 2016, the frequency and volume of its use around the world grew roughly 100-fold. Yet the compound has drawn national bans and courtroom battles worth billions of dollars. Scientific agencies reading the same evidence have split bitterly. How does one molecule kill a plant while aiming at a pathway animals do not have? Why did farmers redesign their crops around it? And how did a corporation, regulators and journalists end up on opposite sides of a single question about cancer?

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• 2. Two Chemists, One Molecule

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  In 1950 a Swiss chemist named Henry Martin, working for the company Cilag, made glyphosate for the first time. He never published the work. Early tests suggested only that the molecule was a weak chelating agent, a substance that grips metal ions. Then it sat forgotten until 1970, when Monsanto in the United States found it again, independently. Chemists there had prepared about 100 derivatives of aminomethylphosphonic acid, hoping to find water-softening agents. Two of them showed weak herbicidal activity. A Monsanto chemist, John E. Franz, was asked to build analogs with a stronger effect, and glyphosate was the third one he made. He later received the National Medal of Technology of the United States in 1987 and the Perkin Medal for Applied Chemistry in 1990. Monsanto patented the weed-killing use in the early 1970s and brought it to market in 1974 as Roundup. The first patent expired in 1991. Even so, Monsanto kept exclusive rights in the United States until its patent on the isopropylamine salt ran out in September 2000. In 2008, scientists at the USDA Agricultural Research Service described glyphosate as a "virtually ideal" herbicide. Why it worked so well on plants, and so little on animals, came down to a single enzyme.

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• 3. Starving the Plant

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  Inside a growing weed, a chain of reactions called the shikimate pathway builds three amino acids: phenylalanine, tyrosine and tryptophan. Animals, including humans, have no such pathway in their genome. Glyphosate blocks an enzyme in that chain, abbreviated EPSPS. X-ray crystallography shows the herbicide sitting in the spot where phosphoenolpyruvate would normally bind, mimicking a transitional stage of the reaction. With the enzyme jammed, shikimate piles up in plant tissue and energy is diverted from other work. Growth stops within hours of spraying, yet the leaves take several days to begin turning yellow.

  The plant takes the chemical in mostly through its leaves and only slightly through its roots. For that reason it works only on actively growing plants and cannot stop a seed from germinating. Once inside, it travels to growing roots and leaves, and that systemic reach is central to its power.

  The name records its parentage, a contraction of glycine and a phosphonate. The first laboratory route reacted chloromethylphosphonate with glycine. Industry now relies on two main methods, both built on the Kabachnik-Fields reaction. The glycine route accounts for a substantial portion of production in China.

  The same chemistry suits it to odd jobs. Farmers spray it on grain just before harvest so the crop dries evenly, though glyphosate is not itself a desiccant. In sugarcane, a pre-harvest dose raises sucrose concentration. In wheat, barley and oats, evenly dried fields can be straight-cut. Growers then skip the step of swathing and drying the crop first, which saves time in northern regions with short growing seasons. Land managers also use it to clear invasive species and to help native plants establish in prairie restoration.

  In 2007 American farms alone applied 180 to 185 million pounds of it, while home gardens used a mere 5 to 8 million.

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• 4. A Gene From a Waste Column

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  Some microbes carry a form of EPSPS that glyphosate cannot jam. Monsanto scientists needed one that resisted the herbicide yet still worked well enough to drive plant growth. After much trial and error, they found it in an Agrobacterium strain called CP4. The bacteria had been surviving in a waste-fed column at a glyphosate production facility. The scientists cloned the CP4 EPSPS gene and transferred it into soybeans. In 1996 those genetically modified soybeans went on sale, the first Roundup Ready crop. Farmers could now spray after the crop emerged, killing weeds while sparing the harvest. Resistant varieties now include soy, maize, canola, alfalfa, sugar beets and cotton, with wheat still under development. By 2023-91% of United States corn and 95% of soybeans came from strains engineered to tolerate several herbicides. So did 94% of cotton. Those herbicides included dicamba, glufosinate and glyphosate.

  Weeds answered with evolution. The first documented glyphosate-resistant annual ryegrass, Lolium rigidum, was reported in 1996 near Orange, New South Wales. The weed specialist Ian Heap earned his doctorate on multiple-herbicide resistance in that same species. By 2014 he called it the "world's worst herbicide-resistant weed." It had turned up in 12 countries and affected over 2 million hectares. In 2004 a resistant Palmer amaranth appeared in Georgia, followed by North Carolina in 2005, and it went on to develop several separate resistance mechanisms. Resistant Johnson grass was found in Argentina, Arkansas, Louisiana and Mississippi. By 2014-23 resistant species had been counted in 18 countries. The pattern fits a line from the literature: resistance evolves after "intense selection pressure in the form of repeated use of a single herbicide."

  Some resistant weeds carry as many as 160 extra copies of the EPSPS gene, according to Monsanto scientists. Farmers have answered with hand-weeding, tractors that turn the soil between crop rows, and other herbicides alongside glyphosate. Ryegrass offers one small mercy. Resistant plants compete poorly against ordinary ones and dwindle when glyphosate is withdrawn.

  Use of glyphosate and other herbicides like 2,4-D to clear milkweed along roads and fields may have contributed to a decline in monarch butterflies in the Midwestern United States. Together with deforestation and adverse weather, the loss of milkweed fed an 81% decline in monarchs. In 2015 the Natural Resources Defense Council sued the EPA, arguing it had ignored warnings about the effect on monarchs.

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• 5. Formulas and Footprints

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  By 2010 more than 750 glyphosate products were on sale worldwide. Glyphosate is an acid, so it is packaged as a salt, and Monsanto's active ingredient is the isopropylamine salt. The molecule enters leaves poorly on its own, so makers add a wetting agent. The most common is tallow amine ethoxylate, usually 10-12% of a concentrate by weight. In an Australian test on ryegrass, a 12% tallow formulation killed 87% of weeds. An alkyl amine alternative managed only 76%, while a 14% tallow mix reached 97%.

  Chinese manufacturers had become the world's largest producers of glyphosate and its precursors by 2014, supplying about 30% of global exports. In 2010 American companies filed a formal trade dispute alleging that Chinese firms were dumping it on western markets.

  The surfactant polyethoxylated tallow amine, or POEA, is where much of the biology gets complicated. A 1997 United States government report put it at 15% of Roundup and 14.5% of Roundup Pro. POEA is more toxic to fish and amphibians than glyphosate alone, so aquatic formulations leave it out. In water its half-life of 21-42 days outlasts glyphosate's 7-14 days. Amphibians are especially exposed because they often breed in shallow, temporary pools where concentrations can run higher. Studies on tadpoles link POEA formulations to gill damage, delayed development and malformations of the tail, mouth, eye and head. Yet a 2013 meta-analysis found glyphosate could not be the major cause of amphibian decline. Most of that decline came before widespread use, or in pristine tropical areas.

  For people, acute toxicity is low. Glyphosate is less acutely toxic than 94% of herbicides in USDA data. Still, deliberate overdoses of concentrate have killed. Swallowing 85 to 200 ml of a 41% solution of Roundup has caused death within hours. Quantities as large as 500 ml have also been swallowed with only mild or moderate symptoms.

  In soil, the molecule clings tightly to mineral particles, and microbes break it down into aminomethylphosphonic acid. Its field half-life is typically 47 days but ranges from two to 197. A site in Texas measured three days, while a site in Iowa measured 141.9. In frozen Swedish forest soils, the breakdown product lingered up to two years.

  Residues in food are small. When EU states tested 6,761 food samples in 2016, 3.6% held quantifiable glyphosate. Nineteen samples exceeded legal limits, six of them honey and eleven buckwheat. A Canadian survey of 7,955 samples found 42.3% with detectable traces but only 0.6% above the limit. One third of the samples over the limit were organic products.

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• 6. Two Verdicts on Cancer

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  In March 2015 the International Agency for Research on Cancer, part of the World Health Organization, placed glyphosate in category 2A, "probably carcinogenic in humans." It cited limited evidence for non-Hodgkin lymphoma in people, plus animal and laboratory studies. The agency judges hazard, not risk. In its own words, "a few positive findings can be enough to declare a hazard, even if there are negative studies, as well."

  Eight months later the European Food Safety Authority reached a different conclusion, calling a cancer hazard unlikely. Its work leaned on a 2013 review by Germany's Institute for Risk Assessment, known as BfR, which examined more than 1000 studies. The BfR replied that IARC had looked at only a selection of what it had reviewed, and pointed to the Agricultural Health Study. In November 2015-96 scientists signed an open letter faulting the BfR report. They said it used unpublished data, lacked authorship, omitted references and disclosed no conflicts of interest. IARC, for its part, uses only published studies, because regulators have let agrochemical companies run their own unpublished research.

  Christopher Portier, a scientist who advised IARC on the assessment, argued in 2016 that the European report gave almost no weight to published literature. In October 2017 The Times revealed that Portier had consulting contracts with two law firm associations representing alleged victims, including a payment of US$160,000. The IARC final report was also found to differ from an interim draft. Text noting studies that found no cancer link had been removed, and "limited evidence" in animals became "sufficient evidence."

  Other bodies sided with EFSA. In 1993 the United States Environmental Protection Agency modelled a worst case, a person eating a lifetime of food from sprayed fields at maximum residue levels, and predicted no harm. It later judged glyphosate "not likely to be carcinogenic to humans." In March 2017 the European Chemicals Agency kept its classification of serious eye damage and aquatic toxicity. It found no evidence of cancer, mutation or reproductive harm, and repeated these findings in 2022. As of 2020, evidence tying long-term exposure to human cancer remained inconclusive. Evidence of a possible risk to heavy occupational users is weak, and none exists for home gardeners. Earlier small studies linking glyphosate to non-Hodgkin lymphoma were later judged likely biased.

  Monsanto, meanwhile, had not waited quietly for the verdicts.

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• 7. The Monsanto Papers

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  In 2017, lawyers pursuing cases against Monsanto made public a trove of internal company documents, which they called the "Monsanto papers." Monsanto had called the IARC report biased and wanted it retracted. The documents indicated a planned public relations effort to discredit it. One piece was a 2015 opinion article in Forbes Magazine by Henry Miller, who did not disclose his link to the company. The New York Times reported that Monsanto asked whether he would write it. He answered, "I would be if I could start from a high-quality draft." Once the connection surfaced, Forbes removed his blog from its site.

  The same lawsuit evidence also surfaced company emails that appeared to show a friendly relationship with a senior EPA official. In August 2019 the EPA announced it would no longer allow labels claiming glyphosate causes cancer, saying they would mislead the public.

  Two Le Monde journalists won the 2018 European Press Prize for a series of articles on the papers, also called Monsanto Papers. Their reporting described letters from Monsanto's lawyers demanding that IARC scientists hand over documents related to Monograph 112, the volume containing the glyphosate finding. Several of those scientists condemned the letters as intimidating.

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• 8. Bans and Lawsuits

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  In May 2015 the president of Sri Lanka banned the use and import of glyphosate, effective immediately. By May 2018 the plantation sector had been allowed to use it again, and the ban was fully revoked in August 2022. Many bans have followed that arc. Thailand's hazardous substances committee voted for a ban in October 2019 and reversed itself in November. A 2018 court ruling temporarily banned it in Brazil before being overturned. Mexico's president announced in August 2020 a phase-out by late 2024. The government postponed it in March 2024 without a new date. El Salvador approved a ban on 53 agrochemicals in 2013, glyphosate among them, and later rescinded the glyphosate ban. Vietnam banned it nationwide in April 2019.

  Colombia has sprayed glyphosate from aircraft over coca fields since 1994. In May 2015 it said it would stop by October, after farmers complained that the spraying had destroyed whole fields of coffee and other legal crops. That ban was later lifted.

  Europe's fight played out in votes. A relicensing vote stalled in March 2016, with France, Sweden and the Netherlands objecting. A temporary extension failed in June 2016. Then, at the last minute, the license was extended for 18 months. On the 27th of November 2017, eighteen member states backed five more years, against a requirement of sixteen states representing 65% of citizens. Germany's agriculture minister, Christian Schmidt, voted yes unexpectedly. His coalition was split, and Germany usually abstains in such cases. In March 2019 the European Court of Justice ordered EFSA to release industry studies on carcinogenicity and toxicity. The renewal review then drew 2400 comments, which EFSA called an unprecedented number. In July 2023 EFSA found no critical area of concern, and in November 2023 the European Commission granted a 10-year renewal.

  National rules differ widely. The Netherlands barred sales to home users in April 2014. France banned Roundup 360 in January 2019, with many farm exemptions. Carinthia in Austria outlawed private use in March 2019. The Austrian parliament passed a national ban in July 2019 that never took effect because of a legal defect. Deutsche Bahn and Swiss Federal Railways announced in June 2019 that they would phase out the herbicide on tracks by 2025. Luxembourg's full ban began on the 1st of January 2022, and the Administrative Court annulled it in April 2023.

  In the United States, glyphosate is not banned federally or by any state, though many local governments restrict it. California moved in 2015 to list it as a carcinogen. Monsanto sued the state's hazard assessment office and its acting director, Lauren Zeise, in 2016 and lost in March 2017. Glyphosate was listed under Proposition 65 in 2017, but a federal court later permanently blocked the warning label. On the 18th of February 2026, President Donald Trump issued an executive order giving some legal protection to producers, citing national food security.

  Since 2018, plaintiffs in United States courts have argued that glyphosate herbicides made by Monsanto, now part of Bayer, gave them cancer. Bayer has paid over $9.6 billion in judgements and settlements, and has also won at least 10 cases. A separate wave hit food makers. In 2016 Quaker Oats was sued over a "100% natural" claim after trace glyphosate turned up in oatmeal. General Mills dropped a similar label from Nature Valley bars.

  The compound has also become a rallying point for activists against genetically modified food, and some claims about it are false. Robert F. Kennedy Jr. falsely asserted that modified crops are nutrient deficient. Stephanie Seneff falsely claimed glyphosate causes autism. In February 2026, Bayer proposed a $7.25 billion class settlement to resolve pending and future cancer lawsuits.

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