Glyphosate (Monsanto’s Roundup) is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses that are known to compete with commercial crops grown around the world. It has several advantages over many herbicides in that it breaks down in the soil into non-toxic organic molecules, reducing or eliminating contamination of groundwater and lower soils.
Monsanto has developed genetically modified (GMO) grains that are resistant to glyphosate, so that agriculture can apply the herbicide to kill the competitive weeds while not harming the crop. This allows farmers to suppress the weeds while allowing better production out of the grain crop.
Whatever the benefits of glyphosate, GMOs and the herbicide are tied together in many minds. And there has been an ongoing effort by many people to claim that glyphosate causes cancer. But let’s look at the science, because maybe we’ll get some information.
What’s this about cancer?
The famous (or is that infamous?) study from Séralini, which claimed that glyphosate and GMO corn caused cancer in rats, is quite popular with the anti-GMO forces. For many reasons, including bad statistics, improper experimental design, and bad conclusions, the article was retracted by the journal.
Because that article was retracted, it doesn’t actually count because it really doesn’t exist (but to be fair, it was eventually, re-published in a very low ranked journal). This story is frighteningly similar to the story of that cunning fraud, Mr. Andy Wakefield, who wrote a fraudulent, and ultimately retracted, article about vaccines and autism. I guess Séralini is the Wakefield of the GMO world.
There are better studies out there–maybe.
There is an ideological subculture that is motivated to blame all the perceived ills of the world on environmental factors and corporate/government malfeasance. Often this serves a deeper ideological drive, which can be anti-vaccine, extreme environmentalism, or anti-GMO. The latest environmental bogeyman making the rounds is glyphosate, which is being blamed for (you guessed it) autism.
Glyphosate is the active ingredient in the herbicide Roundup. It has been widely used for about 40 years, and with the introduction of GM crops that are Roundup resistant, its use has increased significantly in the last 20 years. It has therefore become a popular target for anti-GMO fearmongering.
Glyphosate is one of the least toxic herbicides used. It inhibits the enzyme 5-enolpyruvylshikimic acid-3-phosphate synthase which interferes with the shikimic pathway in plants, resulting in the accumulation of shikimic acid in plant tissues and ultimately plant death. The enzyme and pathway do not exist in animals, which is why toxicity is so low. Still, chemicals can have multiple effects and so toxicity needs to be directly measured and its epidemiology studied.
Experimental evidence has shown that neither glyphosate nor AMPA bioaccumulates in any animal tissue. No significant toxicity occurred in acute, subchronic, and chronic studies.
Therefore, it is concluded that the use of Roundup herbicide does not result in adverse effects on development, reproduction, or endocrine systems in humans and other mammals. For purposes of risk assessment, no-observed-adverse-effect levels (NOAELs) were identified for all subchronic, chronic, developmental, and reproduction studies with glyphosate, AMPA, and POEA.
As pesticides go, glyphosate has very low toxicity, and any dose a person is likely to get exposed to is well below the safety limits.
Elsevier has announced that they are retracting the infamous Seralini study which claimed to show that GMO corn causes cancer in laboratory rats. The retraction comes one year after the paper was published, and seems to be a response to the avalanche of criticism the study has faced. This retraction is to the anti-GMO world what the retraction of the infamous Wakefield Lancet paper was to the anti-vaccine world.
The Seralini paper was published in November 2012 in Food and Chemical Toxicology. It was immediately embraced by anti-GMO activists, and continues to be often cited as evidence that GMO foods are unhealthy. It was also immediately skewered by skeptics and more objective scientists as a fatally flawed study.
The study looked at male and female rats of the Sprague-Dawley strain of rat – a strain with a known high baseline incidence of tumors. These rats were fed regular corn mixed with various percentages of GMO corn: zero (the control groups), 11, 22, and 33%. Another group was fed GMO corn plus glyphosate (Round-Up) in their water, and a third was given just glyphosate. The authors concluded:
The results of the study presented here clearly demonstrate that lower levels of complete agricultural glyphosate herbicide formulations, at concentrations well below officially set safety limits, induce severe hormone-dependent mammary, hepatic and kidney disturbances. Similarly, disruption of biosynthetic pathways that may result from overexpression of the EPSPS transgene in the GM NK603 maize can give rise to comparable pathologies that may be linked to abnormal or unbalanced phenolic acids metabolites, or related compounds. Other mutagenic and metabolic effects of the edible GMO cannot be excluded.
Sounds pretty scary. Now let’s look at the multiple criticisms:
The biggest criticism of the study is the combination of two features – the small sample size and lack of statistical analysis. The entire study is premised on comparing various dose groups with control groups that were not exposed to GMO or glyphosate. And yet, the authors provide no statistical analysis of this comparison. Given the small number of rats in each group, it is likely that this lack of statistical analysis is due to the fact that statistical significance could not be reached.
In other words – the results of the study are uninterpretable. In the retraction statement Elsevier wrote:
Ultimately, the results presented (while not incorrect) are inconclusive, and therefore do not reach the threshold of publication for Food and Chemical Toxicology.
The retraction reads like a long excuse for the editorial failure of the journal, and is disappointing. But at least they ultimately reached the correct conclusion – this paper should never have been published. It slipped through the cracks of peer review.
- Scientific Journal Retracts Anti-GMO Junk Science Study (illuminutti.com)
- The Seralini GMO Study – Retraction and Response to Critics (sciencebasedmedicine.org)
- Seralini GMO Study Retracted (theness.com)
- Study Linking Genetically Modified Corn to Rat Tumors Is Retracted (scientificamerican.com)
Bad science in the paper ‘Long term toxicity of a Roundup herbicide and a Roundup-tolerant GM maize’
Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modiﬁed maize
Spontaneous Tumours in Sprague-Dawley Rats and Swiss Mice