Evidence that Glyphosate causes cancer

April 2014

In March 2013, GM-free Scotland described Gilles-Eric Séralini's controversial GM feeding study on rats as “the first ever life-long study” [1]. This was the first such test of Roundup herbicide and of the Roundup-tolerant maize which accumulates the herbicide. It was not, however, the first life-long feeding-study on glyphosate, the active herbicidal ingredient in Roundup.

A 1995 review of glyphosate toxicology carried out by the Northwest Coalition for Alternatives to Pesticides refers to three life-long studies which were received by the US Environmental Protection Agency (EPA) for its safety assessment. These are unpublished and so little information on the test conditions is available (for example, number of animals used or dosage of glyphosate administered).

However we can ascertain that results from the first one were received by the EPA during 1982 and 1983. It tested Sprague-Dawley rats (the same strain as used by Roundup's manufacturer, Monsanto, and by Séralini), and reported testicular tumours in males and increased thyroid cancers in females.
The second was received by the EPA in1985. This one tested mice and found an increase in a rare kidney tumour in males.

The third study was received by the EPA in 1991. It tested rats of unidentified strain, and found increased pancreas and liver tumours in males together with the same thyroid cancer previously seen in females.

Despite the stated “viewpoint” of one EPA statistician that the EPA's role is “protecting the public health when we see suspicious data”, the Agency seems to have gone to some lengths to avoid seeing anything ominous in the three studies. Policy seems to have been to re-jig the data so that the tumours could be dismissed as false positives; for example, the now familiar trick of adding in a stack of irrelevant historical comparator control values to swamp an inconvenient finding (a.k.a. bad science) got rid of the testicular tumour problem, and the declaration that a lesion in an untreated mouse kidney was actually a tumour despite expert opinion to the contrary (a.k.a. falsifying the data) got rid of the kidney tumour problem.

 COMMENT Interestingly, it didn't occur to anyone at that time to dismiss the results from the Sprague-Dawley rats on the grounds that that strain is prone to cancer in old age. Modern regulators, such as the European Food Safety Authority, have become much more inventive since the 1980s. 

Not highlighted in any of the three studies was the time of onset of the various tumours in the rats' lifespan. This could be a key point because the major concern raised by Séralini's experiment was that, while “In the control group, tumours occurred mostly at the end of life, in the 23rd and 24th months which seems to be normal in these rats”, in the Roundup-fed test animals “palpable tumours begin in the 4th month and explode in the 11th and 12th months. Which corresponds to the age of 35 to 40 years in a human.” (Co-author of Séralini's paper) [2].

Are there any common strands linking these various tumours to a possible common cause, such as glyphosate?

Thyroid cancers of the same type appeared in two life-long experiments. US health statistics in the GM era show a very strong correlation between glyphosate application and thyroid cancer [3].

Liver cancer featured in one life-long experiment. US health statistics in the GM era show a very strong correlation between glyphosate application and liver cancer [3].

Kidney cancer featured in two life-long experiments (in mice reported in 1985, and in rats published in 2012).

The most troubling aspect of all these studies revolves around the endocrine-disrupting properties of glyphosate. Evidence of increased mammary tumours in Séralini's study, increased testicular tumours in the EPA report of 1982, and the finding that glyphosate stimulated proliferation of breast cancer cells in culture[4] could all be linked to hormonal disturbances induced by glyphosate. Actual effects of an endocrine disruptor can vary enormously depending on the dose, gender and life-stage at exposure.


Note that the EPA studies pre-dated GM glyphosate-tolerant crops. This means that, if the levels of glyphosate fed to the experimental rodents reflected expected exposure to the herbicide at the time, they would fall far short of what we experience now.

Today, we have GM crops designed to accumulate glyphosate in food and feed, spraying of Roundup on a massive scale, increased applications needed to combat Roundup-resistant weeds, and steadily increasing 'allowable' limits set by regulators in response to biotech industry demands. The resulting exposure to glyphosate is many orders of magnitude higher than it was in the 1980s.

On top of this, the harmful effects of Roundup formula (with its secret ingredients added to help glyphosate kill cells more efficiently) could be many orders of magnitude greater again.

The cancer link to glyphosate remains unresolved: demand the precautionary principle be applied until the questions raise here have been answered by science and not spuriously explained away by adjusting the data and statistics.

[4] GLYPHOSATE AND CANCER - September 2013
  • Caroline Cox, Northwest Coalition for Alternatives to Pesticides, Glyphosate, Part I: Toxicology, Journal of Pestice Reform 15:3, Fall 1995
  • Glyphosate and Cancer, Institute of Science in Society Report, 26.03.14

1 comment:

  1. Join us and sign our petition to have glyphosate banned from Scotland.


Thanks for your comment. All comments are moderated before they are published.