Glyphosate: Dangerous chemical or anti-GMO bogeyman?


No other chemical in modern agriculture has attracted as much scrutiny and criticism as glyphosate. The herbicide–widely sold generically but also under the trade name of Roundup, and originally patented by Monsanto–has been used in home gardens and by farmers for decades. It has played a key role in the evolution of the genetically engineered seeds that dominate many of the world’s most important crops, including corn, soybeans and cotton. At the same time, it has been linked in some studies that scientists say are of debatable merit to an array of human health disorders, including autism and cancer.

When the European Chemicals Agency announced that its review of the research finds that glyphosate is not a carcinogen, it marked yet another important scientific victory for this favored target of anti-GMO forces.

[The GLP’s coverage of the European Chemicals Agency announcement is here. For more background on glyphosate, read the GLP’s GMO FAQ: “Is glyphosate (Roundup) dangerous?]

Glyphosate history

The herbicide has been vetted repeatedly by regulators in the US, Europe, Canada, Australia and elsewhere. The scientific consensus is that glyphosate is safe when used as directed. Itoriginally was introduced in 1974 by Monsanto as part of its Roundup herbicide for consumers. The substance began a full-scale move into farming in 1996 and 1998, when the company released soybeans and corn genetically engineered to resist its effects. The pairings allowed farmers to kill weeds, without damaging their crops. It went off patent in 2000, freeing other companies to market their own versions, helping it to become the most-used agricultural chemical.

Along the way, the product attracted a small, but vocal, group of critics who have produced studies and reports, often criticized by scientists in the field. Among them is a 2013 analysis by Stephanie Seneff, an MIT computer analyst with no expertise in toxicology, that correlated glyphosate use with various conditions, including autism, depression and Parkinson’s disease. The claims drew sharp criticism from scientists, who argued that Seneff’s work revealed correlation — not causation. Just because two things are happening at the same time doesn’t mean one of them caused the other. For example, the rise in autism also correlates with the rise in organic food sales.

Safety concerns also have been raised by an oft-cited 2013 study by French geneticist Gilles-Éric Séralini, which featured pictures of rats with bodies twisted by cancer allegedly caused by exposure to glyphosate or GMO corn. The controversial study was retracted and then republished later without peer review. The study’s methodology was criticized by scientists and independent oversight agencies around the world, and was reviewed and dismissed by the National Academies its May 2016 report on genetically engineered crops.

Concerns about glyphosate’s possible health impacts increased in 2015 after the International Agency for Research on Cancer, a research arm of the World Health Organization, classified it as “probably carcinogenic,” using what is called a hazard evaluation. The IARC classification was widely circulated by anti-chemical and ant-GMO advocacy groups, which argued for bans or tighter restrictions.

Regulatory agencies in the US, Europe and elsewhere reviewed and, for the most part, rejected IARC’s cancer designation, noting it was based on the questionable quality of the studies evaluated to make its conclusions and questionable methodology on IARC’s part. It also was criticized for focusing on whether glyphosate might cause cancer in workers exposed to extreme doses over extended periods of times – not  whether traces found in our food would pose a danger to consumers.

According to the US Environmental Protection Agency and every independent regulatory agency of note, the herbicide is not considered carcinogenic when used correctly. The European Chemicals Agency has now joined these other agencies, following its announcement. 55Among other recent findings in support of the glyphosate’s safety:

  • In May 2016, a joint panel from the World Health Organization and the Food and Agriculture Organization of the United Nations issued a summary evaluation of glyphosate, concluding it poses no cancer risks as encountered in food and does not impact our genes. The toxicity was so low, the joint committee wrote, it was not necessary to establish a ARfD–an acute toxicity reference dose often used to regulate risk. It also reviewed impact on workers, noting that the only “high quality” study found no evidence of a cancer link.
  • In September 2016, the EPA released a long-delayed report, considered to be one of the most extensive ever undertaken on the herbicide, authored by 13 prominent independent scientists, concluding: …there is not strong support for the “suggestive evidence of carcinogenic potential” cancer classification descriptor based on the weight-of-evidence, which includes the fact that even small, non-statistically significant changes observed in animal carcinogenicity and epidemiological studies were contradicted by studies of equal or higher quality. The strongest support is for “not likely to be carcinogenic to humans” at the doses relevant to human health risk assessment for glyphosate.
  • A June 2015 re-review of glyphosate by Health Canada concluded that products containing glyphosate do not present unacceptable risks to human health or the environment when used according to the proposed label directions.
  • In 2014, the German Federal Institute for Risk Assessment (BfR) issued an evaluation of glyphosate for the European Commission and European Food Safety Authority. The agency said it found no evidence of “carcinogenic or mutagenic properties of glyphosate.”

Hazard vs. risk

Why is there such a discrepancy between the IARC hazard findings and risk assessments of the regulatory and mainstream science communities? Many people misunderstand how IARC and its findings are perceived in the global regulatory framework. For more than 40 years, the agency has assessed 989 substances and activities, ranging from arsenic to sunbathing and hairdressing. And only once has it found something was “probably not” likely to cause cancer in humans. The problem, scientific critics argue, is that almost any substance can be judged toxic, even water, if the ‘dose’ is extreme and the exposure time is long enough.

One of the basic principles of toxicology is that “the dose makes the poison.” Lots of things can cause cancer, but not everything that can cause cancer does. Even for common substances, if you are exposed to enough of it for a long period of time you will experience toxic health effects.

Most scientists believe IARC’s hazard assessments are confusing to the public and the science community, and offer confusing regulatory guidance, noting for example that the sub-group also considers grapefruit juice and working the night shift to be as hazardous as glyphosate. Even more dangerous, in the organization’s opinion, are processed meat, sunlight, oral contraceptives, Chinese-style salted fish and alcohol–on the level of exposure to plutonium.

While IARC declared glyphosate a cancer hazard, its parent organization, the WHO, determined in three other reviews that the herbicide does not pose a cancer risk, and especially not in the minute amounts potentially consumed in food. IARC, in its own fine print, explains the difference between its hazard assessments and the risk assessments done by others:


While IARC’s cancer warning has been roundly criticized by the scientific and regulatory community, the impact of that warning is still being felt. California, for example, responded to the IARC designation by attempting to add glyphosate to its list of chemicals known to cause cancer – referred to as Proposition 65. Monsanto sought help from the courts to stop the action, but was denied in March 2017. If the state follows through, it will force Monsanto and its competitors to label glyphosate products with a cancer warning. It’s impossible to say whether the European Chemicals Agency’s assessment will have an impact on the California situation, but it seems unlikely, considering that the EPA’s September 2016 report – in favor of glyphosate’s safety – didn’t prompt the state to change course.

On the legal front, Monsanto also faces a spate of lawsuits spurred by the IARC cancer report. The lawsuits have been filed on behalf of farmers, landscapers and migrant workers. Among the attorneys who have brought lawsuits is Robin Greenfield, who told CBS News:

“What everyone has in common is that they all used Roundup and they all have non-Hodgkin’s lymphoma.”

Tim Barker is the managing editor for the Genetic Literacy Project. He is based in Orlando, Florida. You can find him on Twitter at @tbarker13.

  • Chester Cheetah

    Hey timbo
    How much did Monsanto pay GLP last year, either directly or through a group it is a member of? Betcha won’t say….

    • Kevin Patti

      Hey Chester, why don’t you provide proof of your accusations?

    • FarmersSon63

      That is the first thing stupid city people claim when they have no clue how to debate the science.

  • Robert Howd

    This article seems a bit confused to me. I think it’s important to note that glyphosate is extremely unlikely to cause cancer in humans who eat trace amounts in foods, but still might have been the cause of the increased incidence of non-Hodgkins lymphoma in farmworkers. These two situations are not incompatible, and thus the IARC conclusion that glyphosate is a probable human carcinogen is not necessarily either wrong or irrelevant. Nevertheless, all evidence points to it being safe as consumed, and thus the shrill protests by anti-GMO activists including Seralini and Seneff are misleading and frankly unscientific.

    • SageThinker

      But, the science around the carcinogenicity in lab animal studies from the 1980s has been doctored and gamed in what i’ve come to call “Monsanto science” which means that vested interest creeps in at so many levels, subtle and gross, and adds up to lack of integrity. It’s been seen with the Greim and Williams review articles being pre-ordained and overdetermined as to outcome, the Greim 2015 article being planned by Monsanto as preemptive ammunition to counter the expected IARC as shown in this slide from a Monsanto powerpoint presentation on strategy to counter expected IARC classification. There are so many examples of shady dealings with the EPA and Monsanto in the 1980s and 1991 memos that there’s nothing worth saving. When the primary research and the review articles are all industry gamed, what hope is there for genuine reliable interpretation?

  • Robert Howd

    California’s Proposition 65 requires cancer warnings on products considered carcinogenic when exposure would be at a level that would cause a cancer risk of 1 in 100,000 or more. Thus one would expect the herbicide containers to contain the cancer warning label, but no foods derived from crops treated with glyphosate would require a cancer warning. However, I don’t know how the cancer risk level might be determined, since the human study of increased non-Hodgkins lymphoma did not include glyphosate exposure estimates, and there were multiple confounders (exposures to other pesticides and risk factors). In my opinion, the animal data were not adequate to base a risk estimate on either. So if OEHHA does list glyphosate under Proposition 65, the unknown warning level is going to cause confusion. Just for clarification, many pesticides are labelled as carcinogens or reproductive toxins under Prop 65, and that does not preclude their use in California.

    • SageThinker

      I have a feeling that foods with glyphosate residue do contribute to increase in cancer rates greater than 1 in 100,000. Pancreatic and thyroid cancers have been significantly on the rise since 1996 or so.

      • Robert Howd

        Yes, US pancreatic and thyroid cancer rates have increased since 1996, but many things have changed in our diets and other aspects of our environments. We can’t just arbitrarily assume the cause is a specific pesticide, with no supporting evidence. Also note that the incidence of non-Hodgkin’s lymphoma, the only tumor type associated (although weakly) with use of glyphosate, has stayed the same between 1996 and 2013, the last year with completed statistics in SEER cancer reports.

        • SageThinker

          Yes, many other things have changed, and i am not arbitrarily assuming anything to be the cause. However, there is some supporting evidence for this supposition. Just making sure you’re not making assumptions about me.

          • JP

            Considering that your evidence is that “you have a feeling,” yes, arbitrarily assuming is exactly what you’re doing.

          • SageThinker

            That’s not my evidence. That’s your assumption you’re imposing upon me from my comment in an empty rhetorical way. You understand human language? I have that feeling based upon a reasonable amount of carefully examined evidence. I could explain it in more depth if you seemed to be here in good faith in this dialog but i get the feeling you’re not, from your comment which embodies an attack.

          • JP

            All I can go by is what you present. And what you present is “I have a feeling,” out-of-context screenshots of studies with your own thoughts scribbled on them and unfounded cries of corruption.

          • SageThinker

            The notice of corruption is not unfounded. It’s a hugely complex topic and you can’t expect me to write a tome for every post. I speak my reckoning from my point of view as the person who i am, and that is quite enough. You then attack me like this because i crossed your agenda.

          • JP

            I don’t have an agenda, Sage. Stop trying to project your witch hunt onto others.

          • SageThinker

            Not projecting. It’s obvious from your words.

  • SageThinker

    Cover ups and lies by Monsanto with the EPA’s help since the 1980s. Here is an excerpt from their 1986 memo in which they reclassified a control group slide to reduce the p-value for a correlation to renal adenomas. If that’s not p-hacking then what is? We ought to look up Dr Kuschner if he’s still alive. Probably he’s not.

    • Robert Howd

      An incidence of 3/50 may be minimally significant, but as the rest of the report indicates, this high dose of about 3% glyphosate in the diet is near the lethal acute dose, and causes significant kidney and liver damage over a lifetime. Kidney responses to repair damage are expected, and adenomas are non-malignant tumors. They are not necessarily considered evidence of carcinogenicity (malignancy).

      • SageThinker

        No argument on that. 30,000 ppm is 30g/kg which is an insanely high dose compared to an average of 3 ppm in Roundup Ready soybeans. These doses are much more realistic:

        • JP

          So, basically, there is no effect until you get to near-fatal concentrations. Awesome.

          • SageThinker

            Nope, that is not a conclusion one can make from this. That’s something you’re overlaying onto this because it fits that apparent agenda you have.