Dr Michael Antoniou answers the question posed by Metafact
Metafact is a fact-checking website on scientific matters. The editor of the website has posed the question, "Is glyphosate carcinogenic?" to experts. The following response was written by Dr Michael Antoniou in collaboration with GMWatch's Claire Robinson.
Is glyphosate carcinogenic?
Metafact, 19 Aug 2018
Governmental food agencies around the world seemed to have flip-flopped on deciding whether glyphosate, the world's most used herbicide, is carcinogenic. I would like experts to share their opinions and evidence, please, to verify this independently.
Michael Antoniou has answered "Likely"
An expert from King's College London in genetics
Monsanto has been ordered to pay $289 million in damages to Dewayne Johnson, who developed non-Hodgkin lymphoma, a type of cancer, after spraying the company’s glyphosate-based weedkiller Roundup. Johnson’s attorneys mostly relied upon industry’s own laboratory animal studies submitted in support of regulatory authorisations for glyphosate use. The vast majority of these studies show that glyphosate is carcinogenic. Johnson’s attorney Brent Wisner said, "On cancer, there are about 20 studies: six to seven in humans, the rest in animals. In all of those studies but about two, the data are clearly and unequivocally positive" (that glyphosate causes cancer).
This is in agreement with the data on glyphosate toxicity evaluation submitted by industry in support of this pesticide’s authorisation within the European Union (EU), which were analysed and [the results] published in a peer-reviewed article. The authors of the analysis found that Germany’s regulatory authority BfR, which acted as the initial rapporteur for evaluating the safety of glyphosate use within the EU, identified 11 significantly increased tumour increases in seven laboratory rodent studies. This is more than sufficient to classify glyphosate as a “presumed human carcinogen” (second in certainty only to a “known” carcinogen), for which only two positive studies are required under EU law. The authors concluded that the EU authorities broke their own rules to classify glyphosate as non-carcinogenic.
In the wake of the court ruling in favour of Johnson, Monsanto issued a statement claiming that glyphosate is not carcinogenic. One of the authorities that Monsanto cites is the US National Institutes of Health (NIH). The link that Monsanto provides takes us to a publication from the Agricultural Health Study, which was part-funded by the NIH. This study looked at possible links between exposure to glyphosate and cancer among pesticide applicators.
The study did not find a link between glyphosate and non-Hodgkin’s lymphoma, the type of cancer that Johnson has and upon which his case is focused. This is not surprising, as even a Monsanto scientist warned back in the 1990s that the Agricultural Health Study assessed exposure in an “inaccurate” manner. However, Monsanto omitted to mention in its statement that in spite of this weakness, the study did find a link between glyphosate exposure and another type of cancer, acute myeloid leukaemia (AML). The increase in AML was not statistically significant, but the authors of the Agricultural Health Study publication were sufficiently concerned that in the abstract they recommended follow-up research.
Other epidemiological research – considered alongside animal studies by the World Health Organisation’s cancer agency IARC in a review that led to its classifying glyphosate as a probable human carcinogen – did find a link between exposure to glyphosate herbicides and cancer.[8,9] The strongest link was with non-Hodgkin’s lymphoma, the type of cancer that Johnson suffers from. Crucially, IARC identified definitive evidence that glyphosate is genotoxic; that is, it causes damage to DNA and thus compromises gene function, which could over time lead to cancer.
Overall, the most comprehensive analysis of glyphosate’s ability to cause cancer is the review of IARC, which considered all peer-reviewed published literature.[8,9] Claims by pesticide industry defenders that this agency is discredited and its scientists biased have been comprehensively refuted by IARC.
In conclusion, there are data from laboratory studies, including animal toxicity tests, and epidemiological investigations to justifiably classify glyphosate-based herbicides as probable carcinogens. Thus the jury’s conclusion – informed by testimony from several expert witness scientists appearing in support of the plaintiff – that Roundup was a substantial contributor to Johnson’s non-Hodgkin lymphoma appears justified. This is especially so in light of his unusually high-level occupational exposure over a considerable period of time.
Nevertheless, there are two important questions that remain to be answered:
1. The toxic potential of the co-formulants/adjuvants (e.g. POEA) is generally ignored by regulators – yet they are present in commercial pesticides, including glyphosate-based herbicides such as Roundup. Do these adjuvants contribute to Roundup’s ability to cause cancer?
2. Does long-term exposure to glyphosate-based herbicides at typical, non-occupational real-world levels of ingestion lead to cancer? Animal studies showing cancer from glyphosate ingestion use doses far higher than those to which most people are typically exposed. However, given that glyphosate has clearly been shown to cause oxidative stress and to be genotoxic (DNA-damaging), it is within the realms of possibility that cumulative damage to gene structure and function from typical real-world levels of glyphosate-based herbicide exposure could ultimately contribute to carcinogenesis.
What is certain is that work in Dr Antoniou’s laboratory has shown that in rats, ingestion of an ultra-low dose of Roundup at a glyphosate-equivalent level of exposure that is many thousands of times below regulatory permitted levels leads to liver damage – in particular, non-alcoholic fatty liver disease and the more severe non-alcoholic steatohepatitis. This is the first investigation to show a direct causative link between Roundup ingestion at an environmentally relevant level of exposure and a serious disease. Thus cancer is not the only issue regarding glyphosate-based herbicide toxicity.
1. Baum Hedlund Law (2018). Lee Johnson vs Monsanto. https://www.baumhedlundlaw.com/pdf/monsanto-documents/johnson-trial/Johnson-Trial-Plaintiff-Closing-Presentation.pdf
2. BBC World Service (2018). Section in “World Business Report: Turkey acts to curb currency crisis”. Broadcast 13 Aug 2018, 23:32. Available on 16 Aug 2018 at https://www.bbc.co.uk/programmes/w172w47k419s26y#play
3. Clausing P, Robinson C, Burtscher-Schaden H (2018). Pesticides and public health: an analysis of the regulatory approach to assessing the carcinogenicity of glyphosate in the European Union. J Epidemiol Community Health, 72: 668-672.
4. European Parliament and Council (2009). Regulation (EC) No 1107/2009 of 21 October 2009 concerning the placing of plant protection products on the market and repealing Council Directives 79/117/EEC and 91/414/EEC. Official Journal of the European Union. 24 November. http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32009R1107
5. Monsanto (2018). The verdict was wrong on glyphosate. 13 Aug. https://monsanto.com/news-stories/statements/roundup-glyphosate-dewayne-johnson-trial/
6. Andreotti G et al (2018). Glyphosate use and cancer incidence in the Agricultural Health Study. J Natl Cancer Inst. 110: 509-516.
7. Email from John Acquavella of Monsanto (1997) cited by Johnson’s attorneys under heading “AHS is incapable of detecting an association”: https://www.baumhedlundlaw.com/pdf/monsanto-documents/johnson-trial/Johnson-Trial-Plaintiff-Closing-Presentation.pdf
8. Guyton KZ et al (2015). Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncol. 16: 490-491.
9. IARC (2015). IARC Monographs Volume 112: Evaluation of five organophosphate insecticides and herbicides. http://monographs.iarc.fr/ENG/Monographs/vol112/
10. IARC (2018). IARC response to criticisms of the Monographs and the glyphosate evaluation, prepared by the IARC Director. January. http://www.iarc.fr/en/media-centre/iarcnews/pdf/IARC_response_to_criticisms_of_the_Monographs_and_the_glyphosate_evaluation.pdf
11. Mesnage R, Antoniou MN (2018). Ignoring adjuvant toxicity falsifies the safety profile of commercial pesticides. Front Public Health, 5: 361.
12. Mesnage R et al (2017). Multiomics reveal non-alcoholic fatty liver disease in rats following chronic exposure to an ultra-low dose of Roundup herbicide. Sci Rep. 7: 39328.
NB: This answer was written in collaboration with Claire Robinson, editor, GMWatch.org