Unyielding is a University of Missouri School of Journalism project for Investigate Midwest.
Missouri has nearly 27 million acres of farmland. Nearly all of it is blanketed by pesticides.
Crop farming is integral to Missouri’s economy, and pesticides are meant to ease the process. But these substances also come with risks.
The level of risk differs depending on who you ask. And in many cases, the United States’ position on regulating these products is more relaxed than in many other parts of the world.
Such differences stem from a host of factors, including the way pesticides are tested, the rigor of the approval process, the standards to which pesticides are held, and — critics argue — the influence of big agricultural corporations on regulatory agencies and lawmakers.
The U.S. system of regulation differs in key ways from some of its counterparts elsewhere in the world, from its reliance on safety testing conducted by the companies manufacturing the chemicals to its standards that, in some cases, permit the use of chemicals banned in other countries.
Critics believe that the system benefits the sellers of pesticides and endangers the public, while advocates say the U.S. takes a more reasonable and realistic approach to risk.
Before any pesticide can be used in the U.S., it must be registered with the Environmental Protection Agency under the Federal Insecticide, Fungicide, and Rodenticide Act.
The registration process calls for the EPA to evaluate the ingredients, the specific site or crop it will be applied to, the expected amount applied, and how it is to be stored and disposed of. These factors are considered for the potential environmental and human health effects from using the product. Risks to ground and surface water also are taken into account.
This process examines the scientific research and risk assessments surrounding each pesticide to determine any potential harm, ensure the product label properly reflects these findings, and provides acceptable risk mitigation practices. The review process is reevaluated for each chemical every 15 years.
Individual states are responsible for following EPA guidelines, but they are allowed to enact more stringent practices, known as primacy.
Missouri’s pesticide use act closely mimics the EPA’s. The state act and the EPA make a distinction between three different classifications of pesticides: general use, minimum risk and restricted use. General-use pesticides are any pesticide that, when used as stated on the label, would “not generally cause unreasonable adverse effects on the environment,” according to the Missouri Pesticide Use Act.
Minimum risk pesticides contain pre-established and tested chemicals listed by the EPA and could be expected to cause light to moderate negative health effects in the event of misuse. These effects can range from blistering rashes to symptoms of the common cold. This list contains chemicals like sodium chloride and even corn oil.
Restricted-use pesticides are understood to possibly cause unacceptable negative effects to the environment and health risks to humans. In one restricted-use pesticide, paraquat, the negative effects can be as severe as death after a handful of days, even with treatment. While not all restricted-use pesticides are this lethal in as short an amount of time, the effects can still be drastic. These pesticides typically receive additional regulatory restrictions.
Sam Polly, director of pesticide safety education at the University of Missouri’s Extension program, previously worked as a commercial applicator. Polly recounts exposure stories of his own accidental experience with minimum risk pesticides that resulted in minor issues. When discussing restricted use pesticides, he shared the story of an applicator who dumped the paraquat he had left over into a coffee cup, planning to deal with it in the morning. But when he later went to dump the coffee mug, muscle memory took over.
“He took a swig of paraquat. I think he lived for 14 days with all the greatest modern medical technology … He just gave up, his body just gave out,” Polly said. “You can’t afford to get one drop on you, much less a glug of it.”
Checking the water
Testing public drinking water is one of the most reliable methods for the state to test whether agricultural contaminants are reaching the public.
The Missouri Safe Drinking Water law requires all bodies providing drinking water to the public to register through the state’s natural resources department, and to submit water quality tests for contaminants listed in both state and federal laws.
“(Missouri is) different than most states because the way most states are set up with the EPA’s rules, the onus is on the water system to not only do the sampling, but also to find a contract lab that will analyze their samples,” said Eric Medlock, the monitoring section chief for the public drinking water branch of the Missouri Department of Natural Resources.. “In Missouri, we have a state statute that requires us (DNR) to provide analytical services for compliance monitoring.”
An exception to this testing is glyphosate, a chemical used in the commercial version of the popular weedkiller, Roundup. According to Medlock, water systems using a chlorine treatment received a waiver to exclude them from glyphosate testing. This is because of the speed at which chlorine breaks down the glyphosate molecule, he said. For water systems without chlorination, they receive an initial test for the chemical. If it is negative, then a nine-year waiver is applied.
Differing standards, different results
The controversy over glyphosate gained national attention because of a series of lawsuits alleging a connection between the chemical and non-Hodgkin lymphoma, a form of lymphatic cancer. Versions of the household product sold in stores since 2023 have replaced glyphosate with a combination of other chemicals.
Dennis Weisenburger, a retired hematopathologist, has researched the potential connection between non-Hodgkin lymphoma and glyphosate over the past decade. Weisenburger also has served as an expert witness in multiple trials that hinge on the discussion over that connection.
Weisenburger conducted his own study, investigating instances of lymphoma in eastern Nebraska.
“In the counties where there was intensive agricultural activity, there was also higher incidence of leukemia and lymphoma,” Weisenburger said.
However, correlation does not necessarily equal causation, he said. Weisenburger continued his research and ran into Aaron Blair’s work, a chief epidemiologist at the National Cancer Institute, who was also studying potential contributors to lymphoma. Together, they worked on a case-control study in the Midwest to research other risks, including agricultural practices. In 2003, their published study concluded that in addition to considering individual and combined pesticide exposures in farmers, the specific chemicals in pesticides should be tested as risk factors for non-Hodgkin lymphoma.
Weisenburger was also a part of a case-controlled study that analyzed data from the North America Pooled Project based out of the Occupational Cancer Research Centre in Canada. In 2019, NAPP released an analysis of a study that provided evidence of an association between glyphosate and non-Hodgkin lymphoma.
Risk versus hazard
The International Agency for Research on Cancer is an arm of the World Health Organization. In 2015, a working group of 17 experts from 11 countries published Monograph 112, which determined glyphosate to be a probable carcinogen. IARC’s study has been referenced in trials around the U.S. to support the argument that glyphosate could cause cancer.
In June of this year, the results of a new international study confirmed the conclusions of Monograph 112.
The EPA maintains its stance that glyphosate does not cause cancer. Its next required review of the chemical’s registration is expected to be completed by 2026.
John McLaughlin is a professor emeritus with the Dalla Lana School of Public Health in Toronto, Canada. He is also a retired member of the research group s that worked on the IARC’s Monograph 112. McLaughlin noted that after agencies receive hazard assessment recommendations from organizations like IARC, they conduct risk assessments of their own.
McLaughlin explained the IARC’s approach to evaluating glyphosate focused on peer-reviewed studies from the larger scientific community, while the EPA relied more — but not exclusively — on unpublished studies commissioned and done by the chemical’s manufacturer or commercial applicants.
McLaughlin cited a publication in 2019 that revealed the studies used by the EPA mostly looked at glyphosate in its near-pure chemical form, or technical form, and were 99% negative for a risk from glyphosate. Out of the 51 studies used by the EPA, more than half were this type of study. In comparison, 70% of IARC’s peer-reviewed studies had a positive risk from glyphosate while looking more at mixtures of glyphosate, resembling products used in the field. Of the 118 studies used by IARC, 70 % were peer-reviewed.
The study of pure glyphosate poses a challenge, as it is not the product commonly used. The majority of real-life exposure to glyphosate comes from glyphosate-based herbicides, products with an amount of glyphosate mixed in with other chemicals or solvents. These mixed products have been shown to change how glyphosate interacts with the body and are more toxic than pure glyphosate.
“The thing that is important in real-world evidence is to look at real-world exposures,” said McLaughlin. “So it’s the product that’s used by people whether it’s in their home or occupation, that constitutes real-world exposure.”
The other key difference in the materials used in the two review processes relates to the exposure method. The EPA primarily looked at exposure via contamination in food, while the IARC’s studies considered more examples of applicators with high rates of direct exposure.
Robert Tarone worked as a statistician for the National Cancer Institute for 28 years, and has served as an expert witness in U.S. trials related to glyphosate use and NHL. He has published peer-reviewed articles criticizing IARC’s process and said that the working group chose to omit data in the final monograph.
He said that IARC’s monograph on glyphosate is an “outlier finding.”
One reason that researchers have proposed, Tarone said, is that while the IARC evaluated the hazard level of glyphosate, the EPA evaluated the level of risk. The difference between the two: hazard measures the potential for harm, while risk measures the likelihood in individual populations.
In the case of glyphosate, hazard would mean the probability of it causing cancer, while risk would help determine whether cancer is a concern based on average exposure levels for humans.
“Hazard is saying: look, at some exposure level, which may be enormous, this agent can cause cancer,” Tarone said.
When an Investigate Midwest reporter reached out to IARC for an interview concerning glyphosate, they responded in an email, “We no longer give interviews on this topic.”
The difference between regulation standards in the U.S. and other parts of the world is also highlighted by paraquat. It is classified as a restricted-use pesticide in the U.S., meaning it can be applied by a commercial applicator or someone supervised by one. In contrast, the European Union removed paraquat from its market in 2007 due to its nearly 50% fatality rate when consumed.
McLaughlin said public perception of a chemical’s safety can be influenced by “junk science,” including research papers written by ghost writers paid by industry. This combines with the fact that industry, government agencies, governments and politicians put barriers to actually advancing real-world evidence that can be useful,” McLaughlin said.
“Rather than to just try and sell a product and just wish that it’s ‘okay’ we [industry, agencies and communities] should actually be monitoring whether things are safe or not,” McLaughlin said.
Stricter standards and better education
Penelope Fenner-Crisp worked as a toxicologist at the EPA for 22 years, including 12 years as a senior manager in the Office of Pesticide Programs. In 1996, two laws that regulate pesticides — the Federal Fungicide, Insecticide and Rodenticide Act and the Federal Food Drug and Cosmetic Act — were updated. Previously, Congress asked the EPA to periodically update its findings, but “the agency didn’t do a very good job doing that,” Fenner-Crisp said.
“The agency has an obligation in the registration renewal process to plumb the literature deeply and not just pay attention only to the registration package that is put together by the company selling the pesticide … but everything else that may be out there,” Fenner-Crisp said.
In 2020, the WHO released guidelines on pesticide legislation to help governments looking to alter or create new regulations or practices. The guidelines touch on a variety of elements from the regulatory to the application process. Recommendations included a pesticide-specific licensing system requiring a separate license for restricted use pesticides rather than only additional training, a licensing system to encourage the use of low-risk products and tying fine amounts to a neutral parameter like the cost-of-living index or the salary of a civil servant.
Polly is also part of a larger pesticide safety education program around the country and in parts of Canada. In most states, the program oversees pesticide application and recertification training programs.
Not all of the WHO recommendations would be applicable or possible in the U.S. today, but routine health assessments for pesticide applicators caught Polly’s attention. Implementing a regulation like this could provide researchers and regulatory bodies with additional data to base their decisions on. Polly was hopeful that if this regulation were to be implemented in the U.S., it would begin to address two of the biggest issues in the industry — accountability and transparency.
“This is a really lousy way to run a society, suing each other, being suspicious of each other, not working together for a common cause. We all want food. We all want a viable economy,” Polly said. “I don’t think even these pro-chemical people want their grandkids getting cancer, but they’re not thinking it through clearly and they’re not being accountable or transparent.”
Polly also thinks everyone needs pesticide training, not just licensed applicators.
“The other issue that’s huge for me and has really slipped through some of the cracks even though it’s so big, and that’s just homeowners or general people,” Polly said. “They can just go buy stuff at Walmart or Home Depot or Lowe’s, and they have zero training.”
Polly reiterated that even common household products like Lysol, when it is misused or overused, can possibly pose a risk that science has yet to study. Even products that may be familiar could have changed the formula, requiring different safety procedures, like Bayer’s removal of glyphosate from new formulations of Roundup.
Outside of MU and Missouri, he has also worked with the Environmental Protection Agency to give webinars to teach people about pesticide safety.
“I remember on that first one I did with EPA in Wichita, people were like ‘Wow Sam, we learned a lot,’ and that’s scary, because these people are in the industry and they learned a lot,” Polly said.
One challenge with efforts to teach pesticide safety that Polly identified is applicators who do not pay attention or take the training seriously. Some of these applicators have been licensed for decades, and don’t think they have anything to learn. However, it only takes one time neglecting to read the label to misuse a pesticide, especially if it’s been months — or years — since they have last looked.
“We have regulations in place, and they kind of get written on the book and not exactly followed,” Polly said.
Polly emphasized the importance of education when it comes to pesticide safety, recommending it be balanced 50-50 with regulation efforts.
“It’s going to take a new generation understanding the issues, being educated and trying to get the message out to people,” Polly said.
Mary McCue Bell contributed to this report.
Unyielding was produced by students at the University of Missouri School of Journalism. The team included researchers, reporters, data analysts, photographers and graphic designers. The students, most of whom were seniors who graduated in May 2025, included:
Reporters: Mary McCue Bell, Alex Cox, Jonah Foster, Prajukta Ghosh, Adeleine Halsey, Ben Koelkebeck, Xander Lundblad, Lillian Metzmeier, Kyla Pehr, Seth Schwartzberg, Savvy Sleever and Mayci Wilderman.
Data and graphics: Alex Cox, Yasha Mikolajczak and Mariia Novoselia
Photography: Michael Baniewicz
For questions about the project, please contact Mark Horvit, horvitm@missouri.edu.
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