Roundup weed killer; does it kill more than weeds? Photo:Bayer AG-Wikimedia Commons
The Jury’s Still Out on Roundup’s Danger to Humans
By Kevin McKeon, Maine Master Naturalist
With gardening season upon us, the bane of weeds arrives. According to worldwide sales, the most effective control for these invaders is glyphosate. Monsanto’s chemical has become ubiquitous for this purpose. We’ve noticed this herbicide sold as Roundup – popular among gardeners here and elsewhere – in the news for several years, so maybe a bit of information is warranted.
“Without pesticides, there would be a 78% loss in fruit production, a 54% loss in vegetable production, and a 32% loss in cereal production,” says a 2021 paper, one of thousands over the past 50 years reporting on the effectiveness, safety, and dangers of pesticides. This eye-opening statistic explains the use of chemicals in food. But the debate lingers regarding many aspects of the most widely used pesticide in the world — glyphosate — especially Monsanto’s (now Bayer’s) glyphosate product, Roundup.
In 1950, Henri Martin, a chemist with the Swiss company Cilag, synthesized a chemical for which the pharmaceutical company had no use, so it was shelved. In 1959, Cilag was acquired by Aldrich Chemical, a subsidiary of Johnson & Johnson, which added Martin’s chemical to its “Rare Chemical Library.” In 1970, while testing various chemicals to use for a water-softening agent, Monsanto chemist John Franz tested Martin’s chemical and found that it had potentially powerful herbicidal properties. After some tweaking, glyphosate was formed, and Monsanto controlled the glyphosate market via patents for the next 25 years.
As the patents were about to expire, a glyphosate-resistant gene was isolated by scientists at Monsanto and the University of Washington. Monsanto then used gene-splicing to create genetically modified organisms (GMOs) that resisted glyphosate’s effects. So now, these “Roundup-ready” crops grown from Monsanto’s patented resistant seeds could survive Roundup’s use to kill weeds, saving substantial time and money while increasing yield.
Glyphosate inhibits plants from forming an enzyme that’s needed to produce certain amino acids and protein vital to plant growth. This plant enzyme is not found in animals, so it’s been advertised that glyphosate is probably harmless to humans — more on this later. After it’s sprayed, glyphosate is absorbed and spread throughout the plant. About three days later, it becomes concentrated at the tips of roots, stems, and leaves. In four to 20 days, depending on species and environmental conditions, the plant dies.
Demand for Roundup exploded with Monsanto’s effective marketing: “One spray is all you’ll ever need,” and “Safer than table salt” made it the world’s first billion-dollar herbicide, responsible for fully half of Monsanto’s sales. When the company’s glyphosate patent expired, others could produce and sell it — but only Monsanto had the GMO seeds unaffected by the herbicide, so could promote lower expenses for higher crop yields. Advancements in technology have allowed Monsanto to tweak Roundup ready seeds’ effectiveness, giving the company leading, industry standard recognition — despite expiring patents. And Monsanto required farmers to sign agreements banning seed-saving and seed re-planting, so they need to buy new Monsanto seed — and Roundup — yearly, which many do due to lower crop production costs.
Glyphosate is released to the immediate soil via dripping, overspray, and from dead plants and roots. It is absorbed by soil particles, eaten by soil microorganisms, and absorbed by adjacent plant roots. Studies show that soil bacteria are the primary forces that break down soil glyphosate into non-lethal substances — mostly carbon, nitrogen, and phosphorus — and do so relatively quickly: About half of the herbicide is broken down in about 45 days, but it can remain detectable in soils for over six months. Also, glyphosate has an affinity to some soil nutrients, particularly metals, which can preclude these nutrients — like disease-fighting manganese, iron, zinc, and boron — from plant use. So, while it’s not considered overly persistent, its health effects on plants can remain for a year or so.
Glyphosate is sometimes sprayed on areas prior to re-seeding or crop rotation. This “burndown application” kills all plants prior to reseeding for a desired crop, producing an effective seed bed and eliminating the need for tilling the soil. However, some burndown/reseeding operations have resulted in fusarium head blight susceptibility on subsequent grain crops, attributed to residual soil-borne glyphosate being absorbed into these non-target grain crops. This blight’s toxins make the crop unsalable, so many grain millers won’t accept glyphosate-exposed grain for processing. This issue offers the argument that soil-infused glyphosate, from both overspray and glyphosate-killed, decaying plants, can persist long enough to weaken desired crops.
But does glyphosate weaken us humans?
The International Agency for Research on Cancer (IARC) says sufficient evidence exists of glyphosate-caused cancer in animals, but limited evidence exists for cancer in humans — so classifies glyphosate as “probably” carcinogenic to humans. Because of the IARC report, the U.S. Environmental Protection Agency (EPA) conducted further studies; its findings agree with its earlier 1992 report that disagrees with the IARC. So, the EPA classifies glyphosate as “not likely” to cause cancer in humans.
A 2023 study by The University of California, Berkeley, found that glyphosate is a probable human carcinogen. A 2024 study by French researchers linked glyphosate levels to infertility in men. The European Food Safety Authority (EFSA) initially determined that glyphosate was a potent carcinogen for humans; but in 2022, the European Chemicals Agency (ECHA) determined that glyphosate did not meet the scientific criteria to be classified as a carcinogenic, mutagenic, or human-reproductively toxic substance — and the EFSA agreed, reversing its previous findings and approving its use in the European Union.
Lawyers have won $175 million to 2.25 billion individual lawsuits against Bayer, claiming Roundup causes cancer, and there’s an $18.25 billion settlement for most of the remaining suits. So, with the variety of contradictory information available, personal awareness of soil and human health issues seems prudent if/when using glyphosate. In Maine, the pesticide-use label is a legal document: Reading, understanding, and abiding by it is the law!
Send questions for this column to kevandpattymckeon@gmail.com.
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