Even when EPA finds a pesticide cancer risk, agency rarely requires warnings

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The US Environmental Protection Agency (EPA) is failing to put warnings on pesticides linked to cancer — even when the agency itself determined a product’s ingredients are carcinogenic, according to two new analyses of federal data.

The EPA has put cancer warnings on 1.4% — 69 of 4,919 — of pesticide labels for products that contain an active ingredient that the agency itself has designated “probable” or “likely” to cause cancer, the analyses found. In addition, just 1.1% — 242 of 22,147 — of pesticide labels that contain ingredients with “possible” or “suggestive” links to cancer have cancer warnings from the EPA.   

The analyses, by the Center for Biological Diversity and the Center for Food Safety, come as one of the world’s top pesticide manufacturers, Bayer, seeks to rid itself of costly litigation over whether its glyphosate-based herbicides cause cancer. The company is pushing the US Supreme Court to rule the EPA should have sole authority over pesticide cancer labels — a ruling that would have far-reaching implications for pesticide labeling. 

The Trump administration is siding with Bayer on the issue and encouraged the Supreme Court to hear the case, which is set to begin in late April. Bayer, which maintains that its glyphosate herbicides do not cause cancer, has also for years led lobbying efforts to bar states from having stricter pesticide labels than the EPA. The new analyses show, however, that state laws, specifically California’s Proposition 65, are the only reason some cancer-causing pesticides have warnings at all. 

The EPA “violated its duty” to protect Americans from harmful products and a Bayer victory at the Supreme Court would only further the “deadly” consequences of inconsistent and inadequate warnings, said Nathan Donley, environmental health science director for the Center for Biological Diversity. 

“The EPA is signaling to the court that it is capable of doing this but we have shown here that the agency is not capable at all,” he said. “The EPA is not requiring cancer warnings on labels that absolutely need them and that the public deserves.” 

No cancer warnings on pesticides “likely” to cause cancer

Donley and colleagues at the Center for Biological Diversity examined over 93,000 historic and currently approved pesticide labels and found that just 311 of the labels contained a cancer warning. Of the 125 active pesticide ingredients currently used that are linked to cancer, products that contain 119 of those ingredients have no cancer warnings, the analyses found.  

“The EPA is signaling to the court that it is capable of doing this but we have shown here that the agency is not capable at all.” – Nathan Donley, Center for Biological Diversity

For example, the EPA considers the insecticide carbaryl “likely” carcinogenic, however, the agency approved language and labeling for a carbaryl insecticide with no mention of cancer. The US government-funded Agricultural Health Study last year found that pesticide applicators in North Carolina and Iowa who sprayed the insecticide carbaryl often during their career have a higher risk of getting stomach, esophageal, tongue and prostate cancers. 

“Even when the EPA acknowledges that there is a link to cancer, the agency is rarely requiring warnings on pesticide labels, so this agency is essentially incapable of providing a reasonable warning to the public,” Donley said. 

The Center for Food Safety’s analysis looked at 570 pesticides that the EPA’s Office of Pesticide Programs tested for links to cancer — including those that are no longer registered in the US. They found that 35% (200) were classified as either “possibly” or “likely” carcinogenic to humans, and for another 11% the EPA lacked sufficient data to make a determination. Of these 200 pesticides that are possible or likely human carcinogens, 125 are still registered for use.

Bill Freese, science director at the Center for Food Safety, said it’s important to examine both in-use and past pesticides because it can take decades after exposure to a carcinogen for cancer to develop. 

The analysis further found the EPA often approves pesticides that exceed the EPA’s “benchmark of concern” for cancer risk, which is one additional cancer case among one million exposed. 

Some examples include the fungicide iprodione, estimated to cause cancer in up to 1.2 people per 10,000 exposed; the fungicide thiophanate-methyl, estimated to cause cancer in up to 4.3 in 10,000 people exposed to it via drinking water; and the herbicide diuron, estimated to cause cancer in up to 8 of 10,000 workers exposed; along with several others. 

“The EPA has actually done these assessments and itself said that these particular pesticides pose risks of cancer,” Freese said, adding that the EPA approves pesticides assuming that workers will wear proper protective equipment such as respirators and gloves but studies show this isn’t always the case. 

“A cancer warning on a pesticide label could greatly increase the use of this personal protective equipment,” he said. “What we’re really talking about are measures to save lives.” 

“What we’re really talking about are measures to save lives.” -Bill Freese, Center for Food Safety

Wendy Wagner, the Richard Dale Endowed Chair in Law and professor at the University of Texas, said the EPA’s cancer-risk determinations already rely on “assumption-laden” exposure models and added that most of the research produced to inform pesticide registrations is coming from industry, so the information guiding registration decisions “is already much more industry-leaning.”

“It’s very hard for the public to challenge an inadequate warning,” she said. “Industry can much more easily say the EPA is requiring too many warnings.”

The EPA did not respond to questions about pesticide labeling and cancer risks.

Bayer labeling litigation 

The Center for Biological Diversity analysis found that 1,250 pesticide labels had cancer warnings due to California’s Proposition 65, which has stricter requirements than federal rules for pesticides. “California’s Prop. 65 labeling is picking up some of the slack,” Donley said. “Having cancer warnings only be required by the federal EPA would leave so many holes, as we see in our analysis.” 

For example, the pesticide ingredients mancozeb and chlorothalonil are both designated “likely” human carcinogens by the EPA, but only include cancer warnings specific to Prop. 65. 

Such state labeling is at the heart of both the upcoming Bayer Supreme Court case and state pesticide “preemption” battles around the country. Since purchasing Monsanto, maker of the glyphosate-based Roundup herbicide, Bayer has faced tens of thousands of lawsuits alleging that its glyphosate herbicides caused people’s cancer, a claim the company denies.

The lawsuits followed a 2015 classification from the World Health Organization’s International Agency for Research on Cancer that deemed glyphosate “probably carcinogenic to humans” with an association to non-Hodgkin lymphoma. Several other studies have linked glyphosate herbicides to cancer.

Last week a gathering of dozens of scientists assessing the last 10 years of scientific evidence on glyphosate issued a consensus statement urging US and European regulators to more tightly regulate the weed killer in light of strong scientific evidence that the pesticide can cause cancer and other health problems. 

“Glyphosate and glyphosate-based herbicides harm human health and can cause cancer. The comprehensive evidence supports this conclusion,” the statement said. “Glyphosate is not the only pesticide that has been inadequately evaluated or regulated.” 

The EPA, however, maintains there is “no evidence that glyphosate causes cancer in humans.” In a December filing with the US Supreme Court, Bayer argues that the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), which governs the registration, distribution, sale, and use of pesticides in the US, preempts such “failure-to-warn” claims against the company. Because the EPA has approved labels — including on glyphosate — with no cancer warning, failure-to-warn claims should be barred, the company maintains.

“Congress created the right incentives by empowering EPA to strike a balance between meeting the needs of farmers and managing inevitable (but not unreasonable) risks, including through labels that neither under- nor over-warn,” the company said in an opening brief sent in February to the court.

The Department of Justice is siding with Bayer, and in a December filing said Bayer’s position on preemption “correctly allows EPA to determine on a nationwide basis what warnings must appear on a particular pesticide’s label to avoid an unreasonable risk to human health.” The New Lede reported that Bayer executives met with EPA officials last year to discuss “litigation” issues – including “Supreme Court Action” over its glyphosate weed killer – just months before the Trump administration took a series of steps to boost Bayer’s case at the high court, according to a June 13 internal EPA email. 

“Congress created the right incentives by empowering EPA to strike a balance between meeting the needs of farmers and managing inevitable (but not unreasonable) risks.” – Bayer opening brief

For years Bayer, alongside more than a hundred other agricultural organizations, has also been lobbying for state laws that bar people from suing pesticide manufacturers for failing to warn them of health risks, as long as the product labels are approved by the EPA. Two states  — Georgia and North Dakota — passed such laws. In addition the House version of the 2026 Farm Bill, which will soon go to a floor vote, would force uniform pesticide labels across the country, which preempts state or local governments from mandating stricter labels that differ from those of the EPA. 

“This provision would handcuff states and local communities when federal regulators drag their feet or bow to industry pressure, and it would slam the courthouse doors on people who’ve been poisoned and harmed,” US Representative Chellie Pingree, a Democrat from Maine, said in a statement.

Freese said that people should have the right to sue a corporation for putting out a product that doesn’t warn of cancer risks and “that’s exactly what Bayer is trying to prevent here.”

“They want to set a precedent with glyphosate that could be used by other companies too,” he said. 

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