Because of much public hype, this product is presently under a cloud of suspicion: The suspicions include the following:
- Cancer Risk: Numerous studies allege that Roundup/glyphosate causes non-Hodgkin lymphoma (NHL) and other blood cancers.
- Negligence/Failure to Warn: Lawsuits claim Monsanto/Bayer was aware of the cancer risk for years yet marketed the product as safe.
- Exposure Routes: Claims involve agricultural workers, landscapers, and residential gardeners who inhaled or had skin contact with the product.
- Misleading Information: Plaintiffs argue the company actively misleadingly reassured the public and regulators about the safety of the product.
THE FACTS
Recently presented by qualified scientists in the critical publication, Skeptical Inquirer, are the chemistry, usage, risks, and underlying misinformation about glyphosate:
Agricultural advances have made farming and our foods safer and more abundant than at any other time in history. Everyone wants safe food and sustainable farming. But modern technologies are victims of their own success, and media systems exacerbate confusion. And while everything—even water—is a chemical, and many chemicals enable food production, the word evokes fear and anxiety. Well-funded disinformation campaigns exploit chemo-phobia to sow fear about the dangers of specific technologies, which undermine consumer confidence in agriculture and our food. Few chemicals are more vilified than the herbicide glyphosate, which is the active ingredient in weed control brands such as Roundup, has been used for decades, mostly without controversy. Many farmers attribute their farms’ survival to glyphosate. Scientific consensus and fifty years of regulatory scrutiny continue to conclude that glyphosate is a benign chemical, safe for use as directed, and poses next-to-no risk to humans. Yet media outlets repeat claims that glyphosate causes everything from autism to cancer to bee extinction. Recently, an article in the prominent medical journal Pediatrics recommended that trace dietary exposures should be avoided by children. Why does a disparity exist between evidence and perception and between experts and “experts”? How do we assess the benefits and any potential risks of glyphosate?
What Is Glyphosate? Glyphosate [N-(phosphonomethyl) glycine] is a non-selective herbicide; in other words, it kills plant species indiscriminately, appearing first on the market as Roundup in 1974. Today, over 750 glyphosate formulations for weed control are produced by numerous companies globally. Glyphosate kills plants by interfering with an enzyme essential for production of key amino acids. Without these amino acids, proteins cannot be synthesized, and the plant dies. All plants have this biochemical pathway, explaining glyphosate’s broad toxicity. Glyphosate has no direct pharmacological effects on animals and humans, which lack this enzyme. Dozens of international regulatory bodies have therefore recognized glyphosate as a low-toxicity chemical with infinitesimal risk to all animals at levels encountered.
Why was glyphosate widely adopted? Historically, farmers planted fields of seeds using other herbicides to control weeds. Soil disruption caused top-soil loss from wind and rain that required labor, fuel, and time. Weed control practices radically changed when scientists invented glyphosate-tolerant (GT) crops—available for public use in 1996. Scientists identified a bacterial variant that was not impacted by glyphosate and transferred this GT-enzyme into corn, soybeans, sugar beets, canola, and alfalfa—another victory for genetic modification! These edible plants then possessed this altered enzyme that was unaffected by glyphosate, so weed control could be accomplished with this singular herbicide. Ease of use, broad spectrum weed control, low cost, minimal environmental impacts, and limited risk to applicators made glyphosate an ideal choice to protect crops from weeds that compete for soil resources.
Legitimate Glyphosate Risks While glyphosate has low acute toxicity to non-target organisms, risks can exist at excessive exposures. The 50 percent lethal dose is 5,000 mg/kg body weight, meaning a 220-pound person would have to consume 500 grams (about one lb) of pure glyphosate to reach that level. While rare reports of self-harm from intentional ingestion of glyphosate exist, it remains a rare cause of human toxicity, certainly not via food or farming exposures. A primary environmental concern is the emergence of phosphorylate-tolerant weeds. Much like antibiotic overuse selecting for bacteria able to survive those chemicals, weed species have similarly adapted. Over forty-eight weed species have developed mechanisms to survive in the presence of glyphosate since use on genetically engineered crops began in 1996. This required companies that produce seeds that incorporated additional herbicides in crop management, which is not ideal when these technologies aim to minimize herbicide use and environmental impact.
When used appropriately with real-world doses, glyphosate poses little risk to the applicator, consumer, or environment as demonstrated with over fifty years of use in farm and residential applications.
Glyphosate Exposure in Humans. Human exposure to glyphosate is physiologically insignificant. Claims that insinuate human risk from glyphosate are based on infinitesimal levels detected on foods or in urine. This underscores a fundamental principle—detection doesn’t equal harm. Every chemical has a toxicity threshold dependent on dose. Pesticides might be detected in food at levels measurable only by the most sensitive analytical chemistry tools. We can detect levels of substances that are irrelevant to our health, measures in parts per billion or parts per trillion. A part per billion (ppb) equals fifty drops of water in an Olympic-sized swimming pool, or one second of time in 31.7 years. Glyphosate exposure levels (maximum residue limits, or MRLs) are set and routinely reevaluated by international agencies to ensure farmer compliance and minimal exposure. For added safety, MRLs are set orders of magnitude below levels that would pose theoretical risks to consumers and account for sensitive populations—children, pregnant women, and those with higher exposure (e.g., farmers). The MRL for glyphosate varies by the crop, but ranges from 0.1 to 400 parts per million (ppm) per day. Detected levels routinely cited in anti-glyphosate campaigns are even far lower than these MRL values. What levels are humans actually exposed to? The water solubility of glyphosate ensures it is rapidly excreted in urine’ and stool, making exposure analysis routine with proper instrumentation. A commonly cited paper in opposition to glyphosate found median glyphosate levels in urine are not only miniscule but nearly identical between people who consume conventional or organic food. A review of the literature reports urine levels are less than 73.5 ppb. For reference, 400 ppm, the highest MRL level of glyphosate, is equal to 40,000 ppb. Levels detected in urine are up to a million times lower than the conservative maximum residue limits, confirming dietary exposure does not pose even a theoretical health risk.
Sensational Unsupported Claims: Glyphosate remains a staple on many farms, so media outlets, activist groups, and even some scientific journals continue to allude to the danger of crops “doused in Roundup.” In 2012, a credible scientific journal published a paper demonstrating that rats fed glyphosate developed tumors. Deeper inspection revealed the authors used a statistically small number of rats prone to tumor growth, and control rats also developed a similar rate of tumors. The paper was retracted by the journal. The European Union sponsored three independent follow-up studies that failed to replicate this claim. Around the same time, an “independent researcher” and an MIT researcher in artificial intelligence published several reviews in low-quality journals that contained evidence of citation bias, selectively using slivers of data from original research that supported the authors’ narrative. One paper, “Glyphosate, Pathways to Modern Diseases II” and “Glyphosate, Pathways to Modern Diseases III,” suggested, without credible evidence, that glyphosate is the cornerstone of gluten intolerance, infertility, miscarriages, birth defects, kidney failure, cancer, and a spate of other disorders. These claims arose from misinterpretation of correlative data related to glyphosate use and Parkinson’s disease, thyroid cancer, and end-stage renal disease. In a subsequent review, they linked glyphosate to autism, chronic fatigue, depression, and Parkinson’s disease. They also claimed that glyphosate is in vaccines, underlying an increase in autism, alleging it will cause 50 percent of children to be autistic by 2025. The origin of the glyphosate in vaccines claim was presented by “Moms Across America,” an organic food activist group with a history of publishing false or doctored information. They also amplified claims made by “U.S. Public Interest Research Group” (PIRG) that glyphosate was present in wine, beer and breast milk. But the commercial kit used is extremely sensitive and validated only for use with water and urine. Breast milk, vaccines, wine, and beer are complex solutions containing countless molecules that could elicit false positive results. Properly executed follow-up work on breast milk failed to detect glyphosate, and 95 percent of wine samples contained less than 5 ppb glyphosate.
Glyphosate is used to control weeds in vineyards, but not applied to grapes or grapevines, so detection of trace residues is not unexpected. Glyphosate was also implicated in chronic kidney disease of unknown origin, based solely on weak correlations. Glyphosate is used to control weeds on tea plantations in Sri Lanka. When farm workers started presenting with an unusual kidney disorder, an investigating medical researcher mentioned glyphosate as a hypothetical cause in a review article, and social media instantly transformed this guess into gospel, despite no causal evidence. This led to a glyphosate ban in Sri Lanka, increasing production costs for farmers and contributing to food shortages. A July 2022 report insinuated that glyphosate causes Alzheimer’s disease, which was supported merely by preclinical research by finding this substance in brains of rodents, wildly extrapolating that to insinuate a link with Alzheimer’s disease. Public communications neglected to mention the mice were fed massive doses of glyphosate daily for two weeks before the assessment, levels that could never be encountered without chugging concentrated herbicide. These are a sample of how, by accident or design, peer-reviewed literature appears to validate unfounded risks associated with glyphosate. Legitimate findings were exaggerated to alarming absurdity by various headlines and class-action attorneys read to cash in on a manufactured crisis. There are several individuals with academic credentials misinforming conferences and publishing unsubstantiated associations between glyphosate and every disease or disorder that plagues us. It is these sensational stories that skew public perception, cause health anxiety, and create a disinformation landscape around one of agriculture’s safest products.
Cancer and the IARC Classification: Activists opposed to biotech crops switched their focus from the crops to the chemistries used on them—and glyphosate was the perfect villain. As acres of glyphosate tolerant crops expanded, so did the use of glyphosate, making it easy to hint at correlations between the disease-of-the-day and increased glyphosate use. This controversy was borne out of slight, statistically non-significant associations between certain cancers in farmers that used glyphosate and some in vitro and animal studies. This was enough for the International Agency for Research on Cancer (IARC), a working group of the World Health Organization (WHO), to label glyphosate as a “probable” carcinogen in 2015. That ignited a firestorm of litigation against Bayer, one of many glyphosate manufacturers. Juries, swayed by emotions and legal narratives instead of science, ruled in favor of the plaintiff’s cases—reinforcing false associations to cancer and making it more challenging for credible science to prevail in public discussion. The issue with a “probable carcinogen” classification? The IARC does not assess risk of exposure, only hazard—which does not consider dosage. This means the question IARC is asking is “Could glyphosate theoretically cause cancer under any circumstance?” and not “Is there evidence of a realistic likelihood that glyphosate causes cancer based on exposures humans may encounter? “The IARC monograph did not suggest a link between dietary glyphosate exposure and cancer. Leaked drafts indicated IARC specifically omitted human evidence that did not support the hypothesis of carcinogenicity. These data were present in draft documents; yet they were deleted from the final monograph. The IARC report augmented deep divisions between scientific and agricultural communities and the public, exacerbated by additional flawed reports shared widely. One pooled analysis exploded across the internet, claiming a 41 percent increase in non-Hodgkin’s lymphoma in exposed groups. However, critics noted the curious grouping of data that led to positive associations, and parallel analyses showed no association. Even a decade after the IARC classification, there is thin evidence to support a relationship between glyphosate exposure and any human cancers. International regulatory bodies. that do assess risk that included robust studies in their assessment have independently concluded there is no relationship between glyphosate and cancer. These include the Joint FAO/ WHO Meeting on Pesticide Residues, the U.S. Environmental Protection Agency (EPA), The National Academies of Sciences (NAS), the European Food Safety Authority (EFSA), the European Chemicals Agency, and Health Canada. All evaluated hundreds of studies across decades of data and concluded there is no solid evidence of glyphosate causing cancer in humans. EFSA rebuked the IARC classification as inappropriate based on data. The European Commission reapproved glyphosate for use until 2033.
Conclusions
Modern agriculture seeks to fill gaps in food security, reinforcing and improving human health. A new eye on sustainability welcomes new (and occasionally old) technology to make land use more efficient and lessen environmental impact. With intrinsic concerns of health, safety, environmental stewardship, and farmers’ economic sustainability, glyphosate has met these goals for five decades. While there is insufficient evidence of health impacts on current exposures, use has been and will continue to be monitored closely. Ongoing research should continue to be alert for any actual risk, extending to all population segments. At present, glyphosate remains useful for farmers to ensure productivity, affordability, and stability of food crops. Although it remains a political target, our job as a scientific and skeptical community is to continue to evaluate claims for veracity and clearly communicate actual risk and benefits to the public.
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