By Anthony Samsel and Stephanie Seneff
Glyphosate is the active ingredient in the pervasive herbicide, Roundup. Its usage on crops to control weeds in the United States and elsewhere has increased dramatically in the past two decades.
The increase is driven by the increase over the same time period in the use of genetically modified (GM) crops, the widespread emergence of glyphosate-resistant weeds among the GM crops (necessitating ever-higher doses to achieve the same herbicidal effect), as well as the increased adoption of glyphosate as a desiccating agent just before harvest.
GM crops include corn, soy, canola (rapeseed), and sugar beet. Crop desiccation by glyphosate includes application to non-GM crops such as dried peas, beans, and lentils.
It should be noted that the use of glyphosate for pre-harvest staging for perennial weed control is now a major crop management strategy.
The increase in glyphosate usage in the United States is extremely well correlated with the concurrent increase in the incidence and/or death rate of multiple diseases, including several cancers.
These include thyroid cancer, liver cancer, bladder cancer, pancreatic cancer, kidney cancer, and myeloid leukemia. The World Health Organization (WHO) revised its assessment of glyphosate’s carcinogenic potential in March 2015, relabeling it as a “probable carcinogen.”[2,3]
Why Other Countries Have Banned Glyphosate
Sri Lanka’s newly elected president, Maithripala Sirisena, banned glyphosate imports as one of his first acts following election.
This action was based on studies by Jayasumana et al. that provided compelling evidence that glyphosate was a key factor in the chronic kidney disease that was affecting an alarming number of young agricultural workers in the northern region,[4,5] and was probably further motivated by the WHO reevaluation of its carcinogenic potential.
Kidney disease is a risk factor for multiple cancers, with kidney dialysis being associated with increased risk of Kaposi’s sarcoma by more than
50-fold, with 3- to 10-fold increased risk of kidney cancer, and 2- to 9-fold increased risk of thyroid cancer.
Many other cancers also show more modest risk increases. A study of rats fed GM maize and/or Roundup in their water over their entire lifespan revealed significantly increased risk of massive mammary tumors in the females, along with kidney and liver damage in the males.
Most of the tumors were benign, but there were three metastases (in female animals) and two Wilm’s tumors found in the kidneys of males, which had to be euthanized early due to the excessive tumors, which grew to more than 25 percent of their body size.
The exposed animals also had a shortened life span compared to the controls.
Glyphosate Has Estrogenic Effects Even at Low Doses
The hormone estrogen was declared to be a human carcinogen by the National Toxicology Program in 2003. Glyphosate has been demonstrated to have estrogenic effects at minute dosages, in in vitro experiments on mammary tumor cells.
Glyphosate was able to induce proliferation in these cells in concentrations of parts per trillion, and it did so through binding affinity to the estrogen receptor and inducing activation of the estrogen response element (ERE).
The fact that an estrogen antagonist, ICI 182780, could inhibit glyphosate’s action demonstrated rather conclusively that it was mediated through estrogen mimicry.
Traditional concepts in toxicology are centered on Paracelsus’ dictum that “the dose makes the poison,” meaning that one should expect an increasing risk of toxicity as the level of exposure is increased.
However, the generality of this concept has been challenged due to the realization that endocrine-disrupting chemicals (EDCs) often show a greater potential to cause cancer at very low doses than at higher doses.
Glyphosate May Disrupt the Balance of Your Gut Microbes
Glyphosate is toxic to many microbes as well as to most plants, and one likely effect of chronic low-dose oral exposure to glyphosate is a disruption of the balance among gut microbes towards an over-representation of pathogens.
This leads to a chronic inflammatory state in the gut, as well as an impaired gut barrier and many other sequelae.
It has become increasingly apparent that chronic inflammation increases cancer risk and, in fact, many inflammatory conditions, such as Crohn’s disease, hepatitis, schistosomiasis, thyroiditis, prostatitis, and inflammatory bowel disease are known cancer risk factors.
In this paper, we review the research literature on glyphosate, with particular emphasis on evidence of carcinogenic potential, which includes glyphosate’s induction of metabolic disorders, oxidative stress, and DNA damage, known precursors to cancer development.
Monsanto’s Early Studies
Samsel petitioned the EPA for copies of documents originating from Monsanto, dating from the 1970s through the 1980s, which described experiments conducted by Monsanto to evaluate whether glyphosate is safe for human consumption.
In this section, we provide a summary of our findings related to those documents, especially with respect to indications of kidney damage, tumorigenicity, bioaccumulation, and glyphosate metabolites.
Changes in the kidneys associated with chronic progressive neuropathy were noted mostly in males, but also in some female animals of both control and treated groups. There was also mineralization and mineralized debris found in the pelvic epithelium of the kidney, most often in females.
Following submission of the study, the EPA subsequently asked Monsanto for a histological reexamination of the low- and mid-dose male animals, which resulted in establishing a no observable effect level (NOEL). In response, Monsanto submitted an addendum to the pathology report.
The results of the addendum summarized the examination of the kidneys and found minimal tubular dilatation accompanied by interstitial fibrosis in all test groups.
Statistically significant increases in tubular dilatation of the kidney were noted. A 50 percent increase in changes to the kidney of the low-dose group and, in the high-dose group, a fourfold increase in incidence was found compared to the control.
Interstitial renal fibrosis begins with an accumulation of extracellular matrix proteins, which is the result of inflammation and injury to the cells, which is found in every type of chronic kidney disease (CKD). Interstitial fibrosis is a progressive pathogenesis leading to end-stage renal failure.
A 26-month long-term study in rats conducted by Bio/dynamics revealed multitudes of tumors in glands and organs. They occurred (from highest to lowest incidence) in the following organs: pituitary, thyroid, thymus, mammary glands, testes, kidney, pancreas, liver, and lungs.
Pituitary, thyroid, and thymus glands control body and immune function, and disruption can induce disease, including cancer. These glands produce many necessary hormones that control numerous biological processes.
Tumorigenic growth also disrupts functionality of the glands and organs where the growth occurs. A Monsanto trade secret document revealed that there were statistically significant lymphocytic hyperplasias of the thymus as well as significant C-cell thyroid tumors.
It should be noted that significant incidence of tumors was found during these investigations. However, to create doubt and obscure the statistical significance of inconvenient findings, which may have prevented product registration, Monsanto used experimental noise from three, five, seven, and even 11 unrelated study controls to effectively eliminate results, as needed.
In some instances, the experiments’ own control showed 0 percent incidence of tumors, while the results for the glyphosate-treated groups were statistically significant. However, through the dishonest magic of comparing the findings to data from unrelated historical controls, they were explained away as a mystery and deemed not to be related to administration of the glyphosate.
Using these deviations effectively neutralized the inconvenient results and thus allowed the product to be brought to market. Had they not engaged in this deception, glyphosate may never have been registered for use.
EPA documents show that unanimity of opinion for product registration was not reached. Not all members of the EPA glyphosate review committee approved the registration of glyphosate. There were those who dissented and signed “DO NOT CONCUR.”
Ridley and Mirly found bioaccumulation of 14C radiolabelled glyphosate in Sprague Dawley rat tissues. Residues were present in bone, marrow, blood, and glands including the thyroid, testes, and ovaries, as well as major organs, including the heart, liver, lungs, kidneys, spleen, and stomach.
The Issue of Control Rats’ Diet
“Historical control data” show that 13 to 71 percent of the lab animals used to conduct toxicity tests on various chemicals would spontaneously present with mammary tumors, and 26 to 93 percent develop pituitary tumors. Their kidney function is also frequently impaired.
A recent study by Mesnage et al. sought to evaluate whether toxic chemicals present in the feed that is standard fare for these animals might be causative for this surprisingly high background rate of disease. Nine out of 13 samples of commonly used laboratory rat feeds tested positive for glyphosate.
Thus, these “spontaneous” disease manifestations may well be due to the toxic chemicals in the feed in the control animals, rather than to some underlying genetic defects, and this fact raises serious questions about the validity of any studies based on such exposed animals as a control group.
Clearly, it is imperative that future studies on the potential toxicity of any environmental chemical address the issue of the possible toxicity of chemicals contaminating the diet of the control animals, and/or the potential impact of nutritional imbalances.
Feeding the control animals an unhealthy diet leads to an increased risk of cancer in the control group, making it much harder to see a signal in the experimental group. Furthermore, since estrogenic chemicals are often more toxic at extremely low doses than at mid-range doses, it is easy to see why the control group may manifest a significant incidence of cancer.
Evidence of DNA Damage from the Research Literature
According to the IARC’s report, while there exists only limited direct evidence of carcinogenicity of glyphosate in humans, strong evidence exists to show that glyphosate can operate through two key features of carcinogens: induction of chromosomal damage and induction of oxidative stress.
A study on sea urchins investigated several different glyphosate-based pesticide formulations, and found that all of them disrupted the cell cycle. The sprays used to disseminate pesticides can expose people in the vicinity to 500 to 4,000 times higher doses than those needed to induce cell cycle disruption.
A study on children living near rice paddy farms in Malaysia revealed DNA strand breaks and chromosome breakage associated with reduced blood cholinesterase levels, which were attributed to exposure to organophosphate insecticides.
The study did not specify exactly to which pesticides the children were exposed, but glyphosate is a general-purpose herbicide whose use in rice paddies in Sri Lanka led to widespread kidney failure among young agricultural workers there, ultimately resulting in a ban on glyphosate usage in Sri Lanka.[4,5]
Impaired Glycine Synthesis
Perhaps surprisingly, a recent study has proposed that glyphosate might serve a useful role in cancer treatment due to its ability to inhibit glycine synthesis.
Glycine is essential for the synthesis of DNA and, therefore, for cell proliferation. In vitro studies on eight different cancer cell lines (including prostate, ovarian, cervical, and lung cancer) demonstrated that glyphosate at doses ranging from 15 to 50 mM was cytotoxic to tumor cells, and that cytotoxicity to normal cell lines required higher doses (e.g., 100 mM).
It was hypothesized that the mechanism of action involved impaired glycine synthesis due to glyphosate acting as a glycine mimetic. In direct contradiction, however, glycine has been shown to prevent tumorigenesis, and it is a potent anti-angiogenic nutrient that suppresses tumor growth. Impaired glycine synthesis likely has other adverse effects as well, such as the possibility that glyphosate interferes with glycine conjugation of benzene-based compounds.
In particular, this is a mechanism used by gut microbes, particularly Bifidobacteria, to detoxify phenolic compounds, producing hippurate (benzoylglycine), a glycine conjugate of benzoic acid, as a mechanism for detoxification. Glycine has been shown to be a limiting factor for hippurate production.
We stated earlier that glyphosate preferentially harms Bifidobacteria, and studies have shown reduced counts of Bifidobacteria in obese rats along with reduced excretion of hippurate. Obese humans have also been shown to have reduced urinary hippurate.
Furthermore, lower urinary hippurate is linked to ulcerative colitis, particularly Crohn’s disease. A Swedish study of over 21,000 Crohn’s disease patients identified increased risk of a broad range of cancers, including liver, pancreatic, lung, prostate, testicular, kidney, squamous cell skin cancer, non-thyroid endocrine tumors, and leukemia.
Crohn’s and inflammatory bowel disease have been increasing in incidence in the USA in step with the increase in glyphosate usage on corn and soy crops.
Colon and Liver Cancer
The incidence of liver cancer in the USA has increased substantially in the past two decades. Nonalcoholic steatohepatitis (NASH) is a fatty liver disease that has been linked to excess dietary fructose. We hypothesize that it is due primarily to the disruption in gut metabolism of fructose due to glyphosate blocking the shikimate pathway.
Exposure of Wistar rats to the herbicide Glyphosate-Biocarb over a period of 75 days resulted in liver damage, including elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), suggesting irreversible hepatocyte damage, as well as large deposition of reticulin fibers containing collagen type III, suggesting liver fibrosis, which is a major risk factor for hepatocarcinogenesis.
Pancreatic cancer is one of the cancers whose incidence is going up in step with the increase in glyphosate usage on corn and soy crops. Glyphosate’s metal chelation effects led to severe manganese deficiency in cows.
Rats fed a diet deficient in manganese showed significantly lower concentrations of manganese in liver, kidney, heart, and pancreas compared to controls. Pancreatic insulin content was reduced by 63 percent, and insulin output was correspondingly reduced, suggesting that manganese deficiency may play a direct role in insulin-deficient diabetes and islet cell stress.
Chronic kidney disease (CKD) and cancer are closely linked in reciprocal fashion: cancer or its treatment can cause CKD and patients with CKD have increased risk of cancer. An in vitro study on rat testis and Sertoli cells demonstrated that Roundup triggers calcium-mediated cell death associated with reductions in levels of the antioxidant glutathione, along with thiobarbituric acid reactive species (TBARS) and protein carbonyls indicative of protein oxidation and glycation damage.
Administration of L-buthionine(S,R)-sulfoximine (BSO), a specific inhibitor of glutathione synthesis, to rats caused reduced glutathione levels in the kidneys and a marked increase in pathologies linked to polycystic kidney disease .
Cataracts and Melanoma
Monsanto’s own studies revealed increased risk of cataracts following exposure to Roundup. Early-onset cataracts are associated with insufficient antioxidative activity and, therefore, are a potential risk of cancer. There is a link between cholestasis and cataracts via poor absorption of nutrients that protect the lens from UV damage. Studies on short-term exposure of catfish to sublethal levels of Roundup revealed toxicity to the gills, liver, and kidneys.
The observed elevated levels of unconjugated bilirubin and alanine aminotransferase (ALT) are indicative of cholestasis, likely in part a consequence of impaired CYP enzyme function. Melanoma is one of the types of cancer that have been linked to glyphosate exposure in agriculture. An age-adjusted analysis revealed an 80 percent increased risk of melanoma associated with glyphosate use in a study on pesticide applicators in Iowa and North Carolina.
The incidence of thyroid cancer in the United States has increased dramatically in the past two decades, in step with the increase in glyphosate usage on corn and soy crops. It is not clear how glyphosate might increase risk of thyroid cancer beyond the general factors already described previously in this paper, but it is possible that impaired selenium incorporation into selenoproteins plays a role.
Breast cancer accounts for one-third of cancer diagnoses and 15 percent of cancer deaths in women in the United States. An in vitro study has confirmed that glyphosate stimulates proliferation of human breast cancer cells when present in concentrations of parts per trillion. This effect is specific to hormone-dependent cell lines, and is mediated by the ability of glyphosate to act as an estrogenic agent.
Striking increases in the incidence of non-Hodgkin’s lymphoma (NHL) cancer have occurred over the past three decades, both in Europe and America.
Agricultural workers have a higher risk of NHL than the general population, but it is difficult to tease out the effects of glyphosate compared to the myriad other toxic chemicals they are exposed to, which also confer increased risk. However, some studies have been able to directly link glyphosate to NHL.
A threefold increased risk of NHL in association with glyphosate exposure was found in a 2002 study from Sweden. A later Swedish study in 2008 of over 900 cancer cases also found a significant increased risk of NHL (OR 2.02). A Canadian study demonstrated a correlation between the number of days per year of glyphosate exposure and the risk of NHL.
Celiac disease, along with the more general condition, gluten intolerance, has recently reached epidemic levels in the United States, and it has been hypothesized that this heightened wheat sensitivity is a direct consequence of glyphosate contamination of the wheat, due to the increasingly common practice of wheat desiccation with glyphosate just before harvest.
Celiac disease patients are at increased risk of cancer, particularly non-Hodgkin lymphoma, and they have statistically a shortened lifespan mainly due to this increased cancer risk.
We have reviewed the research literature on glyphosate and on the biological processes associated with cancer, and we have provided strong evidence that glyphosate is likely contributing to the increased prevalence of multiple types of cancer in humans.
Monsanto’s own early studies revealed some trends in animal models that should not have been ignored.Forty years of glyphosate exposure have provided a living laboratory where humans are the guinea pigs, and the outcomes are alarmingly apparent.
We have shown that glyphosate transforms exposed cells into a tumor-provoking state by suppressing crucial enzymes in the electron transport chain, such as succinate dehydrogenase and fumarate hydratase.
Glyphosate chelates manganese, reducing its bioavailability, and manganese is an important catalyst for MnSOD, which protects mitochondria from oxidative damage that can cause mutations in DNA. Glyphosate also causes impaired metabolism of fructose, due to the accumulation of PEP following blockage of the shikimate pathway.
This leads to the synthesis of multiple short-chain sugars that are known to be highly potent glycating agents, such as methylglyoxal and glyoxalate. Glyphosate is readily nitrosylated, and nitrosyl glyphosate is known to be extremely toxic and carcinogenic. Microbial pathways convert glyphosate into sarcosine, a known marker for prostate cancer, likely due to its nitrosylated form.
An often overlooked aspect of glyphosate’s toxicity is its interference with enzymes that have glycine as substrate, due to mimicry. Phenolic compounds are detoxified by gut microbes through glycine conjugation to produce products such as hippurate. Bifidobacteria are important for the role they play in protecting from these xenobiotics through such conjugation.
Reduced hippurate is linked to Crohn’s diseases and inflammatory bowel disease, which show epidemiological trends that match the increased use of glyphosate on core crops, and which are linked to increased risk of a broad range of cancers, most especially non-Hodgkin lymphoma.
Lymphoma has also been linked to glyphosate through studies of environmental exposure in agricultural settings.
Multiple studies, both in vitro and in vivo, have shown that glyphosate damages DNA, a direct step towards tumorigenicity. These studies have been conducted on sea urchins, fish, mice, and various human cell types in vitro. Children in Malaysia living near rice paddies have evidence of DNA damage.
Epidemiological studies strongly support links between glyphosate and multiple cancers, with extremely well matched upward trends in multiple forms of cancer in step with the increased use of glyphosate on corn and soy crops.
While these strong correlations cannot prove causality, the biological evidence is strong to support mechanisms that are likely in play, which can explain the observed correlations through plausible scientific arguments. Glyphosate’s links to specific cancer types can often be explained through specific pathologies. For example, succinate dehydrogenase deficiency is linked to adrenal cancer.
Selenoprotein deficiency is likely contributory towards thyroid cancer. Glyphosate’s action as an estrogen mimetic explains increased breast cancer risk.
Prostate cancer is linked to sarcosine, a by-product of glyphosate breakdown by gut microbes. Impaired fructose metabolism links to fatty liver disease, which is a risk factor for hepatic tumorigenesis. Impaired melanin synthesis by melanocytes due to deficiencies in the precursor, tyrosine, a product of the shikimate pathway, can explain increased incidence of skin melanoma.
This is compounded by tryptophan deficiency, as tryptophan is also protective against UV exposure. Manganese deficiency stresses the pancreas and impairs insulin synthesis, and this could explain the recent epidemic in pancreatic cancer.
Increased oxalate, due in part to the proprietary formulations, stresses the kidney and contributes to risk of renal tumors. Glyphosate’s accumulation in bone marrow can be expected to disrupt the maturation process of lymphocytes from stem cell precursors. Glycine forms conjugates with organic benzene-derived carcinogenic agents, and glyphosate likely interferes with this process.
Glyphosate’s interference with CYP enzyme function impairs detoxification of multiple other carcinogenic agents, increasing their carcinogenic potential.
Overall, the evidence of the carcinogenicity of glyphosate is compelling and multifactorial. We believe that the available evidence warrants a reconsideration of the risk/benefit trade-off with respect to glyphosate usage to control weeds, and we advocate much stricter regulation of glyphosate.