I don’t often quote the bible, but I’ll snip a phrase from Matthew 7:7. “Seek and you shall find.” Matthew did not have chemistry in mind. My take is that if you test a chemical with enough doses and end points in rodents, you will often find some statistically significant effect. The key ques tion, though, is whether that effect is bio logically meaningful and relevant to human exposure.” That question repeatedly comes up in discussions of glyphosate, the most widely used weed killer in the world. My conclusion? Dietary residues pres ent no risk to the consumer, but a small risk of non-Hodgkins’s lymphoma in applicators who do not use proper protective equipment cannot be ruled out. In 2012, the media fawned all over a paper published by Gilles-Eric Seralini and his group that showed pictures of large tumours on rats that had been fed corn genetically modified to resist glyphosate. The study was widely criticized within the scientific community for using too few animals and using a type of rat prone to spontaneous tumours. The paper was even tually retracted because the evidence was deemed to be “inconclusive.” Nevertheless, the idea that glyphosate is linked to cancer was implanted in the public mind. The controversy picked up steam in 2015 when the International Agency for Research on Cancer (IARC) placed glyphosate in its category 2A, reserved for substances that are “probably carcinogenic to humans.” There is much misunderstand ing about this classification, which is based on hazard, not risk. “Hazard” means that a substance has the capability of causing cancer under some condition. Risk is a determination of whether a substance can cause cancer under real world conditions. Any novel pharmaceutical, food addi tive or pesticide that is introduced requires a determination of the acceptable daily intake (ADI), expressed as mg/kg body weight/ day. This is the amount that can be con sumed every day, over a lifetime, without appreciable health risk. After everything has been factored in, the ADI for glyphosate, as determined by the most stringent regulatory agencies, is 0.5 mg/kg/day. Based on residues in food, a typical daily dietary exposure for people has been found to be 0.001mg/kg which SENSE, NONSENSE AND SCIENCE BY: JOE SCHWARCZ PUTTING CONCERNS ABOUT GLYPHOSATE INTO PERSPECTIVE is 1/500th of the ADI. Furthermore, car cinogenicity in rodents begins at a dose that is roughly 100,000 times greater than the estimated daily glyphosate residue in the human diet. That is why I don’t think there is a need to be concerned about food residues. Occupational exposure is a differ ent story. There are a few case-control studies in which patients diagnosed with Non-Hodgkins Lymphoma (NHL) were compared with people free of this disease and were also surveyed about their use of glyphosate. The natural incidence of this cancer is about 2%, and among the heaviest applicators it was found to be 2.6%, which means roughly an extra six cases in 1,000 people over a lifetime. And, of course, an association can never prove a cause-and- effect relationship. The problem with case-control studies is that they are based on human memory which is not very reliable. Far more relia ble are prospective studies in which subjects record their use of a substance over years and researchers then look at their docu mented health records to see if there is a link. The most famous such study is the “Agricultural Health Study” in the U.S. that followed tens of thousands of pesti cide applicators and found no statistically significant association between glyphosate use and overall cancer or Non-Hodgkins Lymphoma. Given that the evidence of glyphosate being a health concern for humans ranges from scant for occupational exposure to none for consumer exposure, how do we account for the fact that Bayer — the mar keter of Roundup, the most popular glypho sate formulation — has paid out billions of dollars to settle lawsuits that claimed injury due to the chemical. Juries can be swayed by compelling anecdotes, emotional narratives, cherry-picked data, and especially by what is seen as misconduct by big companies. And there has been some of that to be sure. A major paper published in 2000 that was widely quoted to demonstrate the safety of glyphosate was recently retracted because of potential ghost writing by employees of Monsanto, the producer of Roundup at the time. There were also concerns about undis closed financial compensation to the listed authors and too much reliance on unpub lished data supplied by the company. The paper was retracted because of these ethi cal concerns, not because of falsified data as some have claimed. Finally, consider that glyphosate is just one of the thousands of chemicals to which we are regularly exposed and I sus pect that if each of these were tested with the same rigour as glyphosate some adverse effect at some dose in some species would be detected. “Seek and you shall find.” Joe Schwarcz PhD is Director, McGill University Office for Science and Society, Montreal, QC, Canada. 68 I SEED WORLD EUROPE I SEEDWORLD.COM/EUROPE | OCTOBER 2026
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