Is glyphosate toxic to humans?

posted in: Science | 185

Of course glyphosate is toxic! It is a herbicide after all – the whole point of glyphosate (G for short in this post) is to kill unwanted plants. Like all chemicals, including water and salt, G is going to be toxic to animals (including humans) at some dose. Compared to other herbicides, though, G is a pretty safe option for killing weeds. Don’t take my word for it, check out the Glyphosate Technical Fact Sheet from the National Pesticide Information Center at Oregon State. G’s relative safety is one reason why it’s become so popular.

Wheat being harvested. Image by NDSU Ag Comm.
Wheat being harvested. Image by NDSU Ag Comm.

One interesting use of G is to dry wheat before harvest. To help reduce levels of toxic fusarium fungus on wheat, it is good to harvest the wheat as early as possible but you can’t harvest it until it’s dry. So G is used to dry (aka kill) the wheat plants so the grain can be harvested. As long as the G  is sprayed after the plants have fully matured, the G won’t be moved from the plant into the seeds. Here, G is actually helping farmers prevent a legitimately scary toxin from getting into the food supply. Want to learn more? Check out this video: Wheat School- Timing Pre Harvest Glyphosate Application In Wheat.

With G being used not only as a herbicide but also as a drying agent, and not just in our lawns but on our food, should we worry about our safety? In short, no. When used properly, G is quite safe for humans.

The EPA sets maximum safe levels of pesticide residues for crops (called tolerances), based on the latest science. These tolerances are hundreds of times higher than estimated toxic values, and they consider a person’s total exposure to pesticides (with a wide margin of error to protect children and others who may be vulnerable). The USDA tests crops each year to make sure they don’t go above the tolerances. Very few pesticides are found above the tolerance levels (despite what the Dirty Dozen list claims). If the USDA finds any pesticides above the set tolerance, or finds pesticides on crops where they aren’t supposed to be, they report that information to the FDA. The FDA puts the teeth in this whole system. They have the regulatory power to start recalls, levy fines, turn back foods at the ports, and so on (see page 5).

You can find the specific tolerance information for G in the US Code of Federal Regulations, 40 CFR, part 180, subpart C, section 180.364. Some of the tolerances for G were recently increased in the May 1, 2013 Federal Register, Vol. 78, No. 84.

EPA has reviewed the available scientific data and other relevant information in support of this action. EPA has sufficient data to assess the hazards of and to make a determination on aggregate exposure for glyphosate including exposure resulting from the tolerances established by this action. EPA’s assessment of exposures and risks associated with glyphosate follows.

Check out Vol. 78, No. 84 for a full explanation of EPA’s decision as well as insights into the safety of G in general. Scientific documents supporting this decision can be found in docket EPA-HQ-OPP-2012-0132.

Tolerances don’t set your mind at ease? Happily there’s a lot of research to peruse.

If you don’t want to dig through these dense EPA documents, you can take a look at three recent reviews that summarize the literature on glyphosate and humans: Epidemiologic studies of glyphosate and non-cancer health outcomesEpidemiologic studies of glyphosate and cancer, and Developmental and reproductive outcomes in humans and animals after glyphosate exposure. These reviews looked at epidemiological studies, ones that look at disease incidence in large numbers of humans with varying levels of exposure to G or that look at exposure to G in a population that has a disease.

Now, epidemiology isn’t perfect, but with carefully designed studies it can be a powerful way to look for connections in real human populations. Even better when we can look at reviews that put multiple studies all in one place. These reviews cover a lot of studies that find there is no correlation between glyphosate exposure and cancer or non-cancer diseases. Unfortunately these reviews are behind paywalls and I don’t know the funding source behind the reviews, but the EPA documents have summaries of many of the studies within the reviews and more.

There are occasionally alarm-inducing papers like Glyphosate induces human breast cancer cells growth via estrogen receptors. This paper, and others like it, tend to use human cells in a petri dish rather than whole animals. I had the misfortune to do some research on cultured human cells myself and let me tell you, those are some tricky buggers to work with. Even when everything is working perfectly, it’s still very hard to tell if the results you are getting will hold true when repeated in a whole animal model. Something that causes a reaction in naked cells may not react the same when applied to your skin or taken in through your digestive system (both of which have evolved to keep you safe from many things).

Only a combination of animal models and cell studies can give us the full picture (even better if we can pair these up with some epidemiology). The third review above includes some animal studies as do the EPA reports. While I am cautious about cell studies in general, the majority of such studies have not found any cause for concern, as described in Review of genotoxicity studies of glyphosate and glyphosate-based formulations (open access) as well as in the EPA reports.

In any subject there will be a few studies that find something totally different from what is found in the majority of similar studies. In closing, I leave you with this recent strangeness: Glyphosate and AMPA inhibit cancer cell growth through inhibiting intracellular glycine synthesis. This obviously tongue-in-cheek meme plays on so many scaremongering memes created about single studies. As interesting as a single study may be, we must look at the totality of evidence. And so far, the evidence does not show that that glyphosate causes – or cures- cancer.

This obviously tongue in cheek meme plays on

Review Citations

Mink P.J., Mandel J.S., Lundin J.I. & Sceurman B.K. (2011). Epidemiologic studies of glyphosate and non-cancer health outcomes: a review., Regulatory toxicology and pharmacology : RTP, PMID:

Mink P.J., Mandel J.S., Sceurman B.K. & Lundin J.I. (2012). Epidemiologic studies of glyphosate and cancer: a review., Regulatory toxicology and pharmacology : RTP, PMID:

Williams A.L., Watson R.E. & DeSesso J.M. Developmental and reproductive outcomes in humans and animals after glyphosate exposure: a critical analysis., Journal of toxicology and environmental health. Part B, Critical reviews, PMID:

Kier L.D. & Kirkland D.J. (2013). Review of genotoxicity studies of glyphosate and glyphosate-based formulations., Critical reviews in toxicology, PMID:

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Anastasia is Policy Director of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes!