EUGENE, Ore. — Jan. 21, 2025 — Increased exposure to glyphosate, one of the most widely used herbicides in the United States and much of the world, harms infant health in U.S. agricultural counties, according to a new study by two University of Oregon economists.
In a paper published Jan. 14 in the Proceedings of the National Academy of Sciences , Emmett Reynier and Edward Rubin showed that a dramatic increase in the use of glyphosate in U.S. counties most suitable for genetically engineered crops lowered birthweights and gestation, the number of weeks from conception to birth.
They note that because pre-term births, on average, cost an estimated $82,000 in additional medical, educational and other expenses compared to a full-term birth, the national economic impact of the infant health effects translates to between $750 million and $1.1 billion in annual expenses. It does not include other potential health costs.
Reynier is a doctoral candidate in economics whose work is supported by a research fellowship with the U.S. Environmental Protection Agency. Rubin is an environmental economist and assistant professor in the Department of Economics.
The EPA first approved glyphosate for use as an herbicide in the United States in 1974. Federal law requires such decisions to be reviewed every 15 years. In 2020, the agency determined that, if used according to label directions, glyphosate poses no risks to human health. The EPA also found that the herbicide is unlikely to cause cancer in humans.
In 2022, those findings were challenged in court and voided by the U.S. Court of Appeals for the 9th Circuit. They are still under review.
Glyphosate kills plants that are not genetically modified to withstand the herbicide. Farmers can use it to kill weeds in fields planted with crops such as genetically modified corn, soybeans and cotton, which were first permitted for agricultural use in 1996. Since the introduction of genetically modified crops, annual glyphosate use in the U.S. has increased about 750 percent, according to a report from the U.S. Geological Survey.
Reynier and Rubin jointly planned their study to establish a more rigorous basis for understanding the effects of glyphosate on human health.
"We had heard some pretty broad claims about the effects of pesticides on health that seemed to be based more on correlations than on causal effects," Reynier said. "We know people are concerned, and we wanted to make sure we were looking at this rigorously."
In their study, the researchers evaluated human health effects using three types of existing data for rural U.S. counties: genetically modified crop suitability, historical pesticide applications and birth records.
From the United Nations' Food and Agricultural Organization, they gathered data on crop suitability as determined by soils and climate. They used that data to rate agricultural counties on their suitability for raising genetically modified corn, cotton and soybeans. Counties highly suited to such crops, largely places where non-genetically modified versions of these crops were already grown, saw significantly larger increases in glyphosate use after 1996.
Data on births came from the U.S. Department of Health and Human Services. Rubin and Reynier selected a set of more than 9 million birth records in rural counties from 1990 to 2013. All the data were anonymous. Identifying information, such as the precise locations of crop fields and birth parents' homes, was not included.
"By using the mother's county, we matched the infant to the glyphosate exposure estimate. And then we asked how much birthweight changed in the higher-suitability counties versus lower-suitability counties," said Rubin.
Prior to 1996, the data show that trends in two birth outcomes, birthweight and gestation, remained quite similar in counties less and more suitable for genetically modified crops. However, after 1996 infant health deteriorated sharply in counties more suitable for those crops relative to less suitable counties. Rubin and Reynier attribute that relative deterioration to the change in glyphosate use caused by the introduction of genetically modified seeds.
The researchers controlled for any unobserved factors that might have affected health before and after birth from year to year or across counties.
The results imply that at average levels of glyphosate exposure, average gestation was reduced by one day and average birthweight was reduced by 23-32 grams, about 1 ounce.
However, they also found that the changes did not affect all births equally. By considering how shorter gestation and reduced birthweight were spread out across all births, they found that glyphosate's effects were largest among babies with the lowest expected birthweight.
"What this means is that, for whatever reason, if an infant is expected to be at the very low birthweight end of the scale, then glyphosate exposure could affect you more," Rubin said. "It's like being sick and then getting hit with another illness. You're more vulnerable."
Combined with other recent work, the findings challenge the prevailing regulatory position that genetically engineered crops and their associated agricultural practices are safe — and even beneficial — for health, Rubin and Reynier wrote.
"I think something has to change," Rubin said. "Regulators could admit that glyphosate exposure presents some concerns for human health. There's mounting evidence that it could be detrimental."
In addition, he said, there could be greater monitoring of glyphosate use and exposure as well as human health.
"We're still not tracking it in water. We're not tracking it when it's applied," he said. "It does seem like, even if we're not ready to regulate it in a serious way, we could monitor it."
— By Nick Houtman, for University Communications
This project was supported in part by an appointment to the Research Participation Program at the Water Economics Center, U.S. Environmental Protection Agency, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and EPA.
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