Glyphosate is an herbicide that’s widely used in agriculture in the U.S. and around the world. It’s the active ingredient in Roundup, which is commonly applied to crops like soy, cotton and corn that have been genetically modified to withstand the weed killer.
The Environmental Protection Agency maintains that glyphosate is “not likely to be carcinogenic to humans,” although a ruling in 2022 by the United States Court of Appeals for the 9th Circuit has prompted the agency to review the chemical’s risks to human health and the environment.
A new study by economists at the University of Oregon examined how glyphosate may also be impacting the health of infants. It looked at millions of birth records from 1990 to 2013 to see if there were differences in birth weight and gestational length after Roundup use intensified in rural counties that grew genetically modified corn, soy and cotton compared to rural counties that weren’t suitable for growing those GM crops.
The study found that exposure to glyphosate was associated with lower birth weights and shorter gestations, with those effects being greater for some babies more than others.
Joining us to talk about the findings is Ed Rubin, an assistant professor of economics at the University of Oregon.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Geoff Norcross: Glyphosate is an herbicide that is widely used in agriculture around the world. It’s the active ingredient in the weed killer Roundup, which is applied to genetically modified crops like soy, cotton and corn. There are questions about the compound’s safety. The EPA says it does not cause cancer in humans, but a ruling by the 9th U.S. Circuit Court of Appeals directed the agency to look closer.
A new study by economists at the University of Oregon examined how glyphosate may be impacting the health of infants. Ed Rubin is an assistant professor of economics at the U of O. He was one of the authors of the study, and he joins us now. Ed Rubin, welcome to the show.
Ed Rubin: Thank you, Geoff. Thanks for having me, it’s nice to meet you.
Norcross: It’s good to have you. There have been deep concerns about the possible cancer-causing risks of glyphosate. Why did you want to not look so much at that, but at its possible effects on infant health?
Rubin: That’s a great question, Geoff. I guess, to draw a metaphor, it’s a bit of a “canary in the coal mine” idea, where one of the best measured health outcomes that we have is how much an infant weighed at birth. So, we’re really able to just focus on this very well-measured outcome to give us a sense of, is there something going on here that’s detectable through all of the noise in the environment? And secondly, we know that infant health matters a lot for the infants, for the mothers, but also for a lot of later-life outcomes. So it’s a first step in a longer scientific inquiry.
Norcross: Your study looked at birth records from rural counties between 1990 and 2013. Why did you focus on that particular period of time?
Rubin: There’s this agricultural revolution that happens in the mid ‘90s that, if you grew up in a rural community, you probably know about. In ’95, ‘96, ‘97, we received access to this technology called the genetically modified crops, in which the crops are biologically protected from this potent herbicide called glyphosate. In this period, we see these corn, soy and cotton communities, starting in 1996, suddenly inundated by glyphosate exposure. The glyphosate, in the 20 years of the sample, increased 750% in these counties. So we’re able to compare these corn, soy and cotton growing counties to other rural counties that don’t grow these crops, and then disentangle what happens when you see glyphosate use ramp up.
Norcross: You said it ramped up 750% in these counties. That’s breathtaking. Do you have a sense of why it was so universally adopted?
Rubin: Yes, there’s a couple of stories that apply here. One of them is, it really was a magical technology where, in the past, farmers had to very carefully and sparingly apply these very toxic herbicides. And then, suddenly, we enter this new regime, where farmers could spray this potent herbicide directly onto their plants without any fear that they’re going to stunt their plants, or ruin their yields and their livelihoods. So, we basically removed this natural barrier to potential overapplication of these chemicals. They also, I should say, replaced chemicals that were likely as, or more toxic than glyphosate. But again, they were applied at much smaller levels than we’ve seen glyphosate applied, because we removed this natural barrier.
Norcross: OK, well, here’s the big question: What did you find?
Rubin: We find that on average, birth weight and gestational length – the number of days that the child is in utero – both significantly decline with the glyphosate exposure. And on average, at the average level of exposure, for the average rural county birth, this is a 30 gram reduction, which is about 1%. Which may, on average, not sound very large. But if you then think about it, there are many children that are exposed to much larger levels of glyphosate than the average level. In the 90th percentile, people are exposed to three to four times more. So you’re getting birth weight reductions that are about 100 grams.
And similarly, we find that this birth weight loss was not shared equally across all infants. Infants that already were expected to have low birth weight are the ones that bear the majority of this birth weight reduction. So they’re losing 100 grams just to average exposures.
Norcross: Were there geographical differences? I don’t know exactly where you looked, but did this play out harder in some areas than others?
Rubin: Oh, certainly, yeah. These are the areas that are most intensively growing corn, soy and cotton. So it’s gonna look like the rural communities in the South, that historically have grown cotton, and then we’ve got Midwestern communities that are growing soy and corn. These communities are going to look different because these are specific regions of our country.
Norcross: Well, here’s, of course, the big question. You have two graphs, one that shows an exponential use of this glyphosate compound, and then you have these numbers on infant health. Is there actually an arrow causation that you can point to, one causing the other?
Rubin: For sure, that’s the big question here. And the reason why we’re confident or comfortable in making this causal assumption is that, for this to be causal, what we need is no other thing, no other non-glyphosate exposure, specifically affected corn, soy and cotton counties in 1996 and 1997.
So, if there are things – and we were able to control for employment, we’re able to control for demographics, we’re able to control for local income, we’re able to control for pesticides, we’re able to control for a lot – then it would have to be something that specifically affected these glyphosate-intensifying counties at the exact timing of the rollout of genetically modified crops.
Of course, this isn’t quite the level of a randomized control trial, but I think we are … and the referees and the editors were pretty convinced that this seems to have been effective of increased exposure to Roundup.
Norcross: Your partner in this project was a doctoral candidate in economics. I’m struck by the fact that a couple of economists are doing this research – not chemists, not epidemiologists. Are you looking at this through an economic lens?
Rubin: I guess in our flavor of economics, Emmett [Reynier] and I are both environmental economists. Our background is thinking about, how do we properly assess the benefits and costs of a given regulation or a given activity? So, for us, we’ve heard a lot from the chemical industry about the benefits. And we have heard a little bit from court cases that are settled outside of the courts about the potential costs, but there’s a surprising dearth of evidence about the actual health effects of glyphosate. So that’s where we came from.
Norcross: I’m wondering if you have any sense of what your research might mean for this very big question of whether or not to let this compound be used in the herbicides in this country, or anywhere for that matter?
Rubin: I have what I would like to see. I don’t know if that’s what it will mean. What we’d like to see is just to generate a conversation, a revisiting of the conversation around glyphosate. If you go to the EPA’s website, the current, very explicit stance is, “There’s no risks of concern to human health from current uses of glyphosate.” That’s a really strong assertion, particularly given that Monsanto and Bayer have been paying so much money out of court.
There is a growing literature, not just our paper, but two papers out of Brazil, a paper out of Colombia … There’s growing evidence that exposure to glyphosate may not be as safe as the EPA is currently asserting. We’re not asking for a ban, we’re just asking for a reevaluation of this stance.
Norcross: Ed Rubin, thank you so much for this. I appreciate it.
Rubin: It’s been my pleasure. Thanks for having me.
Norcross: Ed Rubin is an assistant professor in the department of economics at the University of Oregon.
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