St. LOUIS — A research group says levels of the controversial and drift-prone weedkiller dicamba have more than tripled in the urine samples of people in the Midwest — even in urban areas.
Since 2017 — when the herbicide took on prominence and widespread use as an “over-the-top” spray for certain crops — there has been a more than 300% increase in levels of the chemical found in the urine of pregnant women in the region, according to the findings from the Heartland Health Research Alliance, a Wisconsin-based nonprofit.
The information was presented this week at the annual meeting of the American Public Health Association in Boston, and raises questions and concerns about possible health risks tied to ambient levels of dicamba in the environment, particularly as sales of the weedkiller have surged.
Chuck Benbrook, the executive director of the organization said the results are remarkable, but not surprising.
“We knew that there was a big increase coming,” he said. “The use of dicamba has increased more in the last five years than any other pesticide in the world.”
Benbrook said the specific health implications of rising dicamba exposure are unclear.
“It’s a reason to pay much more attention,” said Benbrook. “If there is a problem, it’s potentially impacting all of the babies being born in the heavily farmed middle part of the country.”
Bayer, a leading seller of dicamba technology, said the chemical has not been classified as a possible carcinogen according to the World Health Organization’s International Agency for Research on Cancer, and pointed to the U.S. Environmental Protection Agency’s approval of the herbicide.
“When regulators like the EPA assess the safety of pesticides, they take into account actual human exposures and use highly conservative assumptions to ensure there are not health risks to the population,” Bayer said in a statement. “The HHRA’s reproductive health discussion does not take into account these safety standards established by regulators, which misleadingly implies that any exposure poses a health risk.”
Many of the women who took part in the study were from Indiana, including the metropolitan Indianapolis area. Benbrook thinks that the findings indicate exposure to dicamba around the Midwest, given its prevalence in agriculture, and soybean farming in particular.
Dicamba has been around for decades, but its use has soared in recent years, ever since Monsanto introduced crop varieties that are genetically engineered to withstand the chemical. That gives farmers who buy those seeds the ability to spray dicamba directly onto their crops to control weeds — especially ones that have developed resistance to Roundup, the longtime weedkilling workhorse.
Dicamba use remains high in places like Southeast Missouri’s Bootheel region, where varieties of both soybeans and cotton can tolerate the spray.
Bayer acquired Monsanto, the Creve Coeur-based agribusiness giant, in 2018.
Dicamba is notorious for its “volatility” — meaning its tendency to turn into a vapor that goes into the air, before ending up somewhere else. So although farmers with dicamba-tolerant crops don’t risk harming their own fields with the chemical, other nearby crops, plants and trees can get damaged by its airborne movement.
In recent years, increased use of the herbicide coincided with thousands of dicamba-related complaints of crop damage, spanning millions of acres of farmland. Dicamba disputes have created a rift in agriculture, anchored lawsuits that have levied enormous financial damages against its producers, and even helped spark at least one deadly confrontation on the Missouri-Arkansas border.
Kevin Bradley, a plant science professor at the University of Missouri who has closely tracked dicamba issues, said he recently attended a meeting in Nebraska where a survey showed dicamba damage remains the top issue among farmers.
Formal dicamba complaints have slowed, in part because many farmers have switched to dicamba-tolerant seed varieties to shield themselves from damage. And people have also stopped bothering to report cases to state departments of agriculture because they generally lack the time and resources to investigate a high volume of damage reports.
Lawyers are still tracking dicamba damage complaints, and they are keenly interested in a potential new frontier of future cases that examine the public health implications of the chemical’s increased prevalence in the air.
“There’s just more and more of it out there,” said Paul Lesko, a St. Louis-based lawyer involved with dicamba cases. “You’re dosing populations with dicamba.”
It might take a while, though, before any possible health linkages surface. A 2020 study from researchers within the National Institutes of Health, for example, found dicamba was associated with heightened risks of liver and bile duct cancer, with lags of up to 20 years.
In its statement in response to the HHRA findings, Bayer cited an EPA report: “When used according to label directions, dicamba is safe for everyone, including infants, the developing fetus, the elderly and more highly exposed groups such as agricultural workers.”
Benbrook and HHRA members have been involved in separate lawsuits examining whether Roundup causes cancer.
The HHRA findings will be published in a journal in the coming months, Benbrook said.
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