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The Impact of Glyphosate on Human Health

There is a lot of confusion about whether the commonly used herbicide glyphosate ("Roundup") is safe. In this review, Cliff Harvey PhD looks at the evidence from reviews of the literature on the health effects of glyphosate.

Key points

  • Very high doses of glyphosate are demonstrably inflammatory and damaging to the kidneys, liver, gastrointestinal tract, and microbes (in animal studies
  • There is little strong evidence that current levels of glyphosate exposure increase the risk of cancer or other major disorders in humans
  • One review has indicated a significant increase in ADHD associated with increased glyphosate exposure

Glyphosate is a herbicide (“Roundup”) that has become the most commonly used agricultural chemical in the world. There has been a large amount of controversy around the use of this herbicide, especially its possible relation to cancer with the International Agency for Research on Cancer (part of the World Health Organisation of the United Nations) concluding that it is likely to be carcinogenic, while other reviews have disputed this finding, and further papers debating the likely or possible health risks and safety of the herbicide for other health outcomes.1

It is clear that the use of glyphosate is enormous and that the chemical can be found ubiquitously in the environment, in water, and in the foods we eat. Glyphosates ubiquitous use has led to it being found in many common products including cereals and grain products, human milk, tampons, medical gauze, honey (both organic and non-organic), and it has also been detected n human urine, demonstrating exposure.1, 2 There are also very important considerations not just to health, but the environmental impacts on ecosystems from the presence of glyphosate runoff and accumulation in soil and bodies of water.3, 4

What health effects have been demonstrated in animal research?

High doses administered to animal subjects can cause kidney damage, reduced growth rates, liver enlargement and inflammation, and gastrointestinal disorders,1 and is likely to be both genotoxic,5 and reduce sperm concentrations (based on mouse research).6 It is also likely that glyphosate through inhibition of the EPSPS enzyme, can destroy bacteria important to human health as part of the intestinal microbiome,1, 2 and this has provided a controversial hypothesis that glyphosate use may be linked to autism spectrum disorder through the inhibition of the microbiome and resultant growth in clostridia species in the gut.7

It is likely that glyphosate can destroy bacteria important to human health

Animal studies have shown that doses upwards of 100 mg/kg of body weight per day could cause a range of detrimental effects on the liver, bladder, thymus and might be associated with weight gain, colonic ulceration, stomach inflammation, cataracts, liver enlargement, hyperkeratosis, and kidney cell death.8 However, many of these adverse effects were observed at much higher dosages.

What health effects have been demonstrated in humans?

Overall, systematic reviews and meta-analyses of the effect of glyphosate on cancer are inconclusive and there is no strong evidence that glyphosate causes cancer.9, 10 Despite the evidence being unclear at best or showing no real association between glyphosate and cancer, the International Agency for Research on Cancer listed glyphosate as a probable carcinogen. Subsequent analyses by the European Union and by the World Health Organisation and Food and Agriculture Organisation suggested no risk.8, 11 Further reviews, taking into account additional data also disagreed with the IARC report and found no reliable cancer risk.8, 12, 13 Other reviews have shown no reliable or significant genotoxic risk.14

Debate still rages among practitioners and researchers on the carcinogenic potential of glyphosate. If glyphosate is carcinogenic in the amounts that people are regularly exposed to, the reasons are probably complex in nature and may include effects on the microbiome and endocrine system, some of which may take some time to express in observational evidence. It is therefore important that research continues into the use and rising exposure of humans to glyphosate.2

Does glyphosate pose a cardiovascular risk?

Based on results from several mammalian studies (in rats and rabbits), it has been suggested that glyphosate overdose (in workers) might cause conduction disturbances in the heart, and arrhythmias, leading to possible cardiac events.15

Glyphosate and pregnancy outcomes

 A review of 12 studies on the effects of glyphosate on birth defects, abortions, pre-term deliveries, small for gestational date births, childhood diseases, altered sex ratios, and time-to-pregnancy in glyphosate-exposed populations found no significant associations between this herbicide and adverse pregnancy outcomes.16. There was a significant association however in people who apply glyphosate occupationally and Attention Deficit Hyperactivity Disorder (ADHD) (OR = 3.6, 1.3-9.6). However, a recent (2018) review by graduate students at George Washington University found a significant association with neurodevelopmental effects in infants.17

What are ‘safe’ exposure levels in humans?

A review of studies (> 3000 subjects) found that the average urinary levels of glyphosate in occupationally exposed subjects varied from 0.26 to 73.5 μg/L, while urinary levels from environmental exposure ranged from 0.16 to 7.6 μg/L. Of the studies reviewed, two also measured trends in exposure over time, with both showing increasing numbers of people with detectable glyphosate in their urine over time. 18 So, it is clear that exposure is increasing over time and occupational exposure results in a 2- to 10-fold increase in glyphosate levels in the body.

It is clear that exposure to glyphosate is increasing over time

A European Union toxicological assessment set an Acceptable Daily Intake level of 0.5 mg per kg of body weight per day in humans,8  while the United States Environmental Protection agency suggested a ‘no adverse effects level’ (NOEL) of 100 mg per kg per day and an adjusted daily intake level of 1 mg per kg body weight per day.

However, a 2018 review discussing the implications of the IARC categorisation of glyphosate as a carcinogen proposed that the daily intake thresholds be reduced to 0.175 mg/kg/day to bring the recommendations into line with those recommended by multiple research groups.2

Summary and conclusions

  1. High doses of glyphosate are demonstrably inflammatory and damaging to the kidneys, liver, gastrointestinal tract, and microbes
  2.  There is little strong evidence that current levels of glyphosate exposure increase the risk of cancer or other major disorder in humans
  3. Significant increases in ADHD have been associated with increased glyphosate exposure

Overall, the evidence shows a demonstrable effect of high dose glyphosate on a range of health outcomes in animals and it could be assumed that these are likely to occur in humans. However, at current exposure levels, there does not appear to be an appreciable risk to humans but exposure to glyphosate is increasing over time and there may be a significant effect on attention and hyperactivity in children and there is a plausible risk for other health outcomes. It seems prudent to limit exposure to glyphosate by:

  • Reducing its use around the home (by using non-herbicide/pesticide gardening techniques),
  • Using water filters that remove glyphosate
  • Choosing organic foods (more likely to contain less glyphosate residue)
  • Wearing protective clothing and breathing apparatus if occupationally exposed to glyphosate

References

1.            Torretta V, Katsoyiannis IA, Viotti P, Rada EC. Critical Review of the Effects of Glyphosate Exposure to the Environment and Humans through the Food Supply Chain. Sustainability. 2018;10(4):950.

2.            Davoren MJ, Schiestl RH. Glyphosate-based herbicides and cancer risk: a post-IARC decision review of potential mechanisms, policy and avenues of research. Carcinogenesis. 2018;39(10):1207-15.

3.            Richmond ME. Glyphosate: A review of its global use, environmental impact, and potential health effects on humans and other species. Journal of Environmental Studies and Sciences. 2018;8(4):416-34.

4.            Sviridov AV, Shushkova TV, Ermakova IT, Ivanova EV, Epiktetov DO, Leont’evskii AA. [Microbial degradation of glyphosate herbicides (review)]. Prikl Biokhim Mikrobiol. 2015;51(2):183-90.

5.            Ghisi NdC, Oliveira ECd, Prioli AJ. Does exposure to glyphosate lead to an increase in the micronuclei frequency? A systematic and meta-analytic review. Chemosphere. 2016;145:42-54.

6.            Cai W, Ji Y, Song X, Guo H, Han L, Zhang F, et al. Effects of glyphosate exposure on sperm concentration in rodents: A systematic review and meta-analysis. Environmental Toxicology and Pharmacology. 2017;55:148-55.

7.            Argou-Cardozo I, Zeidán-Chuliá F. Clostridium Bacteria and Autism Spectrum Conditions: A Systematic Review and Hypothetical Contribution of Environmental Glyphosate Levels. Medical Sciences. 2018;6(2):29.

8.            Tarazona JV, Court-Marques D, Tiramani M, Reich H, Pfeil R, Istace F, et al. Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC. Archives of Toxicology. 2017;91(8):2723-43.

9.            Acquavella J, Garabrant D, Marsh G, Sorahan T, Weed DL. Glyphosate epidemiology expert panel review: a weight of evidence systematic review of the relationship between glyphosate exposure and non-Hodgkin’s lymphoma or multiple myeloma. Critical Reviews in Toxicology. 2016;46(sup1):28-43.

10.         Chang ET, Delzell E. Systematic review and meta-analysis of glyphosate exposure and risk of lymphohematopoietic cancers. Journal of Environmental Science and Health, Part B. 2016;51(6):402-34.

11.         Authority EFS. Conclusion on the peer review of the pesticide risk assessment of the active substance glyphosate. EFSA Journal. 2015;13(11):4302.

12.         Williams GM, Aardema M, Acquavella J, Berry SC, Brusick D, Burns MM, et al. A review of the carcinogenic potential of glyphosate by four independent expert panels and comparison to the IARC assessment. Critical Reviews in Toxicology. 2016;46(sup1):3-20.

13.         Brusick D, Aardema M, Kier L, Kirkland D, Williams G. Genotoxicity Expert Panel review: weight of evidence evaluation of the genotoxicity of glyphosate, glyphosate-based formulations, and aminomethylphosphonic acid. Critical Reviews in Toxicology. 2016;46(sup1):56-74.

14.         Kier LD. Review of genotoxicity biomonitoring studies of glyphosate-based formulations. Critical Reviews in Toxicology. 2015;45(3):209-18.

15.         Gress S, Lemoine S, Séralini G-E, Puddu PE. Glyphosate-Based Herbicides Potently Affect Cardiovascular System in Mammals: Review of the Literature. Cardiovascular Toxicology. 2015;15(2):117-26.

16.         de Araujo JSA, Delgado IF, Paumgartten FJR. Glyphosate and adverse pregnancy outcomes, a systematic review of observational studies. BMC Public Health. 2016;16(1):472.

17.         Ramadan M, Perry M. Human Evidence for Parental Glyphosate Exposure on Developmental Malformations and Neurodevelopmental Effects: Systematic Literature Review via the Navigation Guide Methodology. 2018.

18.         Gillezeau C, van Gerwen M, Shaffer RM, Rana I, Zhang L, Sheppard L, et al. The evidence of human exposure to glyphosate: a review. Environmental Health. 2019;18(1):2.

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