For most of 2021, a team of scientists was diligently retrieving urine samples from 40 pregnant people in southern Idaho.

They wanted to measure exposure to glyphosate — the most used pesticide in the world — over an extended period of time, and to understand if living near farmland affected a person’s exposure risk.

The study, published in this month’s issue of Environmental Health Perspectives, found that those who lived near an active agricultural field (less than a half-kilometer, or one-third of a mile) had higher concentrations of glyphosate in their urine during the glyphosate spraying season. During the spray season, they also had higher concentrations of glyphosate in their urine compared to people who lived further away.

However, during the parts of the year when glyphosate wasn’t being sprayed, concentrations for people living near and far from farm fields did not vary widely.

The findings suggest that living near an agricultural field is a potential exposure source for glyphosate, though the exact means of exposure is still not known, said Cynthia Curl, an associate professor in Boise State University’s School of Public and Population Health who helped organize the study.

Agricultural fields are sprayed for glyphosate and glyphosate-based herbicides, such as Roundup, to kill weeds. Though glyphosate has existed for 50 years, its increased use over the past two decades corresponds to an increase in growing genetically engineered crops that can withstand being sprayed with it, Curl said, like corn, soybeans, and alfalfa. About 250 million pounds of the herbicide are applied in the U.S. each year, according to the study.

The scientists coordinated with staff at several Idaho health districts to recruit pregnant participants hailing from Nampa, Caldwell, Meridian, Garden City, Twin Falls, Jerome, Gooding, Shoshone, and Heyburn.

For the participants living near farm fields, alfalfa was the most common crop next to participant’s homes, followed by corn, the study said.

Though glyphosate is not recognized by the U.S. Environmental Protection Agency as causing cancer, the World Health Organization’s International Agency for Research on Cancer has said it is likely a carcinogen to humans. Four studies have found that glyphosate exposure has adverse effects on birth outcomes, including pre-term birth, shortened gestation time — longer than pre-term, but not full-term — and reduced fetal growth.

While the study observed pregnant people because “we know that’s a potentially vulnerable time period,” the results “should hold for anyone,” Curl said. Non-Hodgkin lymphoma, in which cancer cells form in the lymph system, is the main type of cancer associated with glyphosate exposure, she said.

Curl intends for future studies to explore just how people living near agricultural fields are exposed to the pesticide.

“We can’t figure out what the appropriate intervention is going to be to try to reduce that exposure unless we know exactly how it happens,” Curl said, “but it’s important to have this new information that it is happening.”

Asa Bradman, a public health professor at the University of California, Merced, who was not involved with the study, said that the study represents a significant step toward learning more about people’s glyphosate exposure.

“This study is really important because it provides information about what we’re actually exposed to, and then, a future step might be to look at these exposures in relation to health outcomes,” Bradman said.

A MORE DETAILED GLYPHOSATE PICTURE

Unlike other chemicals, which can get stored in the body long term, glyphosate takes just 5.5-10 hours to exit the body.

“It’s not like this exposure happens and you’re stuck with it,” Curl said. “The problem (could be) if the exposure is repeated and constant.”

That’s why the researchers involved in Curl’s study wanted to take a longer approach to studying glyphosate exposure. While other studies had collected urine samples from people at a single point in time, Curl’s team believed it was important to take samples frequently from people living both near and far from agricultural fields over many months, including during the season when glyphosate is sprayed. The study subjects provided urine every other week from February 2021-December 2021, throughout their pregnancies, which were sent to the Centers for Disease Control for processing.

The study is the second to be published analyzing data collected from the Idaho participants. Another study conducted by Curl’s team looked more specifically at the interplay between diet, proximity to agricultural fields, and the effects of spray season on glyphosate exposure. Over two weeks in June 2021, within the known spray season for glyphosate, the researchers assigned the Idaho study participants to purchase and eat organic or conventional foods for one week; they then switched to the other diet for the second week. During that two-week period, participants provided urine samples nearly every day.

The researchers had thought that eating an organic diet would help both those who lived away from agriculture and those who lived near it to reduce their glyphosate concentrations. But that was not entirely the case. While those living away from agricultural fields were able to reduce their glyphosate concentrations by 22-43%, those living close to agriculture fields saw almost no decrease. That suggests that living close to an active farm field has a bigger effect on exposure than diet during the spray season, that study said.

UNDERSTANDING EXPOSURE PATHWAYS, HEALTH RISKS

One source of glyphosate exposure is people’s diets, but unlike other pesticides that can become airborne and drift away from where they are applied, glyphosate is not thought to be volatile, or travel through the air, Curl said.

However, the fact that people living near farm fields during spray season had higher concentrations of glyphosate compared to people who lived farther away indicates that spraying could indeed be a source of exposure, the study said. It could be that some of the herbicide drifts through the air into people’s homes and is absorbed through people’s skin or lungs. Or, it could attach to dust in the home, or attach to soil or dust particles that blow into people’s homes. Other studies have shown that some pesticides can become part of house dust, leading to exposure both during spray season and at other times of the year.

Learning how people are exposed to glyphosate would help determine how to limit that exposure, Curl said.

“Other studies of other types of pesticides have recommended closing windows if you know that a field next to you is spraying, or asking your neighbor farmer to notify you when they’re spraying so you can close the window,” she said. “If it’s in the house dust, deep cleaning can be recommended. But until we know the exact mechanism, we can’t really make those recommendations for glyphosate.”

Despite the lack of scientific consensus on the chemical’s health risks, Curl said efforts to limit exposure to it could be justified.

“I feel like we’re still catching up with this chemical in terms of treating it like the most commonly used agricultural chemical that it is,” Curl said. “The precautionary principle suggests that we try to lower exposures to chemicals until we know they are safe, rather than the other way around.”