Syngenta’s secrets – What the company didn’t tell the EPA about its “blockbuster” paraquat pesticide

Sweden started ringing the alarm bell more than 40 years ago, banning the weed killing chemical paraquat in 1983. One by one, other countries around the world did the same as evidence of paraquat risks to human health mounted. Even the Chinese government, which owns the longtime paraquat maker Syngenta, halted use of the pesticide a decade ago after conducting its own studies on paraquat safety and finding troubling results.

In the US, Vermont also recently banned paraquat, with lawmakers there citing risks that include an association between paraquat and Parkinson’s disease shown in years of scientific research.  And California regulators announced paraquat makers voluntarily agreed to stop selling the chemical after the state identified health concerns in new research. Several federal lawmakers have pushed for a nationwide ban.

Yet amid the global cloud of concern, the US Environmental Protection Agency (EPA) continues to greenlight paraquat use on millions of acres, and has downplayed the significance of science linking paraquat to Parkinson’s, an incurable brain disease. The agency said in June it would hold a roundtable over the summer to re-examine the “safety challenges” associated with paraquat. But no such event was held or has been scheduled.

Now, clues to how and why the US remains one of the world’s last large markets for widespread paraquat use are coming to light through troves of internal Syngenta records recently revealed through litigation.

The records show that as paraquat markets around the world started crumbling over concerns for public health, Syngenta fought to keep a tight hold onto the US market, where use of paraquat nearly tripled between 2000 and 2018, a time period when dozens of other countries were banning paraquat.

Notably, internal corporate records, depositions and other records show that both before and during this time frame, Syngenta did not share certain internal data and other information with the EPA regarding paraquat health effects and risks despite federal legal requirements for companies to report information about “unreasonable adverse effects” of their products.

Among the data not shared by Syngenta were analyses of how quickly the chemical could permeate clothing; how fast it could absorb into an applicator’s skin and bloodstream; information about how mixing paraquat with surfactants – a common practice by farm workers – could increase absorption, and information demonstrating dire risks to the brain.

At the same time the company was holding back adverse information, the records show the company was developing and promoting science showing paraquat safety that it could tout to the EPA, including one study published in 2016 that company insiders noted would be “invaluable in supporting our work”.

In 2022 and 2023, The New Lede and the Guardian obtained and revealed a set of internal corporate records showing that Syngenta and its predecessor corporate entities used an array of secret tactics for decades to downplay and discredit science linking what the company called its “blockbuster” weed killer to Parkinson’s and other chronic health issues.

The newly released files, totaling roughly 3,700 pages, provide more insights into the company’s handling of paraquat concerns as well as multiple examples of information Syngenta did not report to the EPA. The records were submitted to a Pennsylvania state court where hundreds of lawsuits have been filed by people with Parkinson’s alleging they developed the disease from exposure to paraquat products. The Pennsylvania cases are among over 10,000 similar lawsuits filed in the last several years around the country.

In the face of the ongoing litigation, which has already cost the company at least $187 million in a 2021 settlement and an undisclosed further amount for additional settlements since then, Syngenta announced earlier this year it would stop all global production of paraquat. The company says that there is no actual link between paraquat and Parkinson’s disease, and that its decision was purely based on market factors. The settlements include no admission of liability.

Other suppliers continue to sell in the US, however, as the EPA maintains that there is no “clear link” between paraquat exposure from regular use and “adverse health outcomes such as Parkinson’s disease and cancer.”

Critics say the story of paraquat is bigger than Syngenta, and is a case study in the failures and frailties of the EPA and a system that does more to protect corporate profits than consumer health.

And critics note that revelations about certain data not shared with the EPA is particularly concerning now, coming just months after the US Supreme Court issued a ruling declaring the EPA as the preemptive authority for determining when a pesticide product needs to include a particular health warning.

“When the pesticide companies know from their own studies that their pesticides are harmful and don’t tell the public or regulators, then they are knowingly contributing to people getting sick and dying.” – Tracey Woodruff, Stanford

“When the pesticide companies know from their own studies that their pesticides are harmful and don’t tell the public or regulators, then they are knowingly contributing to people getting sick and dying,” said Tracey Woodruff, professor of epidemiology and population health at the Stanford University School of Medicine.

Syngenta rejects the claims and says it takes the safety of its products very seriously.  A company spokesperson said Syngenta has never knowingly failed to provide regulators with relevant and required information. 

When asked about the omissions of information, the EPA said in a statement that it “cannot speculate on how this additional information would impact EPA’s assessment,” but noted it has based its paraquat assessments on an “extensive database of information.”

The agency pointed out that the paraquat review is ongoing, and said that companies must submit information “regarding any unexpected or unreasonable adverse effects resulting from their product’s use to EPA.”

“If information exists that has not been submitted to EPA, EPA wants it so that any protections developed are rooted in gold standard science and reflective of the full universe of data,” the agency said. “Failure to comply is a direct violation of federal law,” the agency said.

“Bad news”

In the US, paraquat is often used by farmers to control weeds before planting their crops and to dry out crops for harvest. It is used in orchards, wheat fields, pastures where livestock graze, cotton fields and elsewhere. It is regulated, as are other pesticides, under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA), which requires that a company holding a pesticide registration must submit “factual information regarding unreasonable adverse effects” to the EPA even after a pesticide has been approved and is on the market.

EPA guidance on how to interpret the requirements states that information must be submitted if “the registrant knows, or should reasonably know, that the information, alone or in conjunction with other information, might raise concerns about the continued registration of a pesticide or about the appropriate terms and conditions of registration of a pesticide.”

Yet in a document included in a court filing in the paraquat litigation, Syngenta acknowledged that as of the date of that document – January 2025 – it had no record of providing the EPA with a long list of reports and research that it possessed pertaining to paraquat and potential health impacts. 

When asked about the court records detailing data not shared with the EPA, the company said none of it was relevant to the US market or to EPA oversight and would not have changed the regulatory view of paraquat. The company said it has never “deliberately withheld pertinent information from the US EPA, or any other regulatory authority around the world” and has “always fully complied with all EPA data requests and provided relevant study data, in line with EPA’s regulatory requirements.”

One omission of information that may have been particularly significant to farmers, however, relates to the use of surfactants when paraquat is sprayed. Concerns about surfactants, which increase the ability of an herbicide to penetrate plant tissue, have been a topic of study for years within Syngenta, the documents show. Labels on the company’s US products have long recommended that users add surfactants prior to spraying paraquat.

But since at least the 1970s, the company has had information that paraquat can be more toxic when mixed with surfactants. In the 1970s, company executives considered selling paraquat products with surfactants already added. In a 1975 correspondence, however, a company scientist noted that the possibility of registering a paraquat product already mixed with a surfactant “appears very undesirable due to increased toxicity.” Data from company studies on dogs at that time showed the addition of surfactant to paraquat increased the rate of absorption into the bloodstream from the gut.

Over subsequent years, and well into the 2000s, the company continued to gain knowledge about the potential for health impacts when paraquat is mixed with surfactants, including its ability to absorb through skin and through nasal membranes. The company did not share at least some of those findings with the EPA, including some studies it conducted on animals exposed to paraquat mixed with surfactants, according to deposition testimony and Syngenta’s court admissions.

Syngenta denied in the court filings that surfactants will “normally increase the absorption of paraquat and hence increase its toxicity.” And a company spokesperson said the surfactant used in Syngenta’s Gramoxone product was “specifically selected not to accelerate epidermal penetration.” The company said numerous studies show surfactants have “no significant impact on dermal absorption of paraquat.”  The company additionally said studies show no effect on the nervous system.

• Data showing that Syngenta’s Gramoxone paraquat product “almost immediately” penetrated cotton and other clothing materials, including untreated Tyvek materials commonly used in protective apparel. Though the study was done in the mid-1980s, Gramoxone labels, including the most recent, have stated for years that users can wear “long-sleeved shirt and long pants.”
• A 1988 analysis of paraquat absorption in the urine and blood of people spraying the pesticide over three days that found “an unexpected number” of positive urine tests. A number of workers had paraquat in their plasma as well. Company notes stated that the detection of paraquat in plasma “was the first time it had been observed” and that it could relate to “a problem that may arise with the EPA.”
• In 2007, another evaluation of paraquat in the urine of workers spraying the chemical brought “bad news.” Email correspondence shows two of the small group of sprayers showed levels of paraquat that vastly exceeded “acceptable operator exposure levels” (AOEL). “This is bad news whichever way you look at it,” a Syngenta scientist wrote in an internal June 2007 email.
• A 2007 analysis of scientific literature related to the ability of paraquat to get into the brain that Syngenta received from a former company scientist, which noted “beyond doubt” that research showed it could enter into and kill key brain neurons in animal studies, one of many communications discussing evolving knowledge about paraquat’s ability to get into the brain.

• Syngenta also acknowledged not informing the EPA when a Mexican government agency determined there was a “broad association” between a paraquat exposure and development of Parkinson’s when evaluating benefits for a longtime Syngenta pesticides plant manager who developed Parkinson’s.
• And, as TNL and the Guardian previously reported, the company did not share with the EPA the results of two internal animal studies conducted in the early 2000s by scientist Louise Marks that found paraquat exposure caused significant loss of brain cells until roughly 15 years after the studies were completed. The company sent the study findings after a lawyer suing the company threatened to go to the EPA himself with the material, deposition testimony showed. Syngenta did give the EPA a letter summarizing an additional Marks’ study finding similar results in 2006 but did not share the full summary or the facts of the two other studies, according to testimony by a top company scientist.

In its defense, Syngenta notes in a court document that the EPA has “never cited or sanctioned Syngenta for failing to comply” with its disclosure obligations with respect to paraquat. And the company said for each instance of not sharing something with the agency, there were other factors and findings negating or reducing the significance of the information. The company said, for instance, that findings of paraquat in urine were not a “regulatory or toxicological concern” because most paraquat absorbed into the body is rapidly excreted through urine.  And the company said that data showing higher than acceptable exposures were “not representative of normal paraquat use.” Additionally, the company noted that many studies were conducted in other countries with formulations not used in the US. It also said that EPA guidance regarding company requirements under the Federal Insecticide, Fungicide and Rodenticide Act have “evolved”, and the company has followed “processes designed to comply with its evolving obligations…”

The company said claims that it did not provide regulators with proper information are “inaccurate and misleading.”

But Tim Fort, professor of Business Law & Ethics at Indiana University, said in an expert report filed on behalf of plaintiffs in the litigation that Syngenta absolutely circumvented the intention of the law.

“Syngenta has substituted its own judgment for what is submittable in contravention of EPA Guidance. It has also determined from its own, unsupported anecdotal awareness that it does not have to submit materials to the EPA. Both of these undermine the capacity of the EPA to regulate paraquat’s safety all while Syngenta claims that the product is safe because of an EPA process which it systematically undermines,” his report states.  

Wendy Wagner, a law professor at the University of Texas who has served on several National Academies of Science committees, said FIFRA requirements for pesticide companies to report information to the EPA about product risks are essential.

When that doesn’t happen, she said, it leaves “a lot of holes in our regulatory system with pretty obvious consequences for public health protection.”

The EPA overall is far too reliant on pesticide companies to give them information they need to properly evaluate product safety, Wagner said.

Needing “a lot of luck”

Farmers have long been assured by Syngenta, which brought paraquat to the market in the 1960s through a corporate predecessor, that there is no credible evidence of a connection between Parkinson’s and its weed killer.

But concerns about such a causal connection accelerated in the 2000s as several researchers published studies supporting such a link.

In a 2001 email, a company scientist told colleagues that the new research could “alert EPA to further reviews at some time in the future,” according to deposition testimony.  And a 2001 internal company strategy document stated “Our efforts will be to steer the focus of serious research away from paraquat … and on to other agents … ”

By 2003 the company had set a goal to “raise the level of proactive regulatory defence of paraquat globally,” while noting that the US was a leading market for its Gramoxone brand. Syngenta’s corporate campaign to defend and promote paraquat use then accelerated alongside the science indicating harm.

A big part of the effort was the publication of studies addressing the paraquat and Parkinson’s links found by outside researchers. In one email, a Syngenta scientist wrote to a colleague “what we want to do is brush aside 10 years of research by others and replace it with our own.”  The company would “employ the best people to help us,” and would need “impeccable data” as well as “a lot of luck”.  It was important that Syngenta’s research be “dead solid airtight and self-contained,” and credible with the larger science community as well as “the judge and jurors.”

The company’s internal documents indicate that secrecy was an element of the campaign. In a 2007 email, company officials discussed a need to minimize written communication on an analysis of paraquat and Parkinson’s data. Even that message itself should not be shared in writing, but should be communicated “verbally” to staff.

And in a 2008 email, company scientists were warned against written discussions about conducting certain studies and chided for writing that “a major objective of this programme is to reduce the risk” that Syngenta might lose lawsuits brought by people with Parkinson’s. “Please can we call a halt to this correspondence,” a Syngenta executive wrote to colleagues.

In a 2011 email, Syngenta scientists discussed a “PD [Parkinson’s disease] Risk Factors Paper” they wanted to be published as an “independent review” under the authorship of a lead researcher outside the company named Jack Mandel. Mandel, formerly an epidemiologist with the University of Toronto school of public health at that time was a scientist with the contract research company Exponent, according to the email.

The email between the Syngenta scientists discussed making revisions, “editorial changes,” and working to “refine and improve” the manuscript even though no Syngenta employee would appear as an author. The correspondence stated that communication to the outside author “ideally” should “occur verbally”, and that because the paper is to appear independent, “we cannot be seen to try to influence.”

It additionally noted that Mandel “prefers not to engage in such exchanges because he knows he might be a witness someday.”

Mandel authored multiple papers for Syngenta, the record shows. It is not clear how much he was paid by Syngenta, though in deposition testimony one senior Syngenta scientist confirmed a company contract with Mandel for $160,000 for one study.

One paper published in 2011 with Mandel as a lead author, titled Epidemiology and Etiology of Parkinson’s disease: A review of the evidence, examined connections between pesticides and Parkinson’s, but also looked at a potential connection to a range of lifestyle choices, such as consumption of dairy products, coffee, and alcohol. With respect to pesticides, the paper concluded there was a positive association but evidence was “limited.”  The paper stated that Mandel received “research support” but no “payments or incentives” and said the work was supported by a Syngenta “grant”.

A 2012 paper authored by Mandel and two other outside scientists criticized other studies that linked paraquat to Parkinson’s. That paper stated it was supported by an “unrestricted grant from Syngenta,” and noted that the authors had previously worked as paid consultants but said the contents of the paper had been under the “full control of the authors for the duration of this effort”.

Mandel was also an author of a 2016 paper that concluded there was insufficient evidence to definitively tie farming, pesticide use and other factors to Parkinson’s. On this paper, Mandel was joined by a Syngenta scientist and three other consulting scientists.

Emails cite “3 years” of Syngenta’s work for that 2016 paper, which a company scientist said “ranked up there with the most difficult papers we have done”, and was being published “just in time.”

The records show Mandel, working through Exponent, was also engaged by Syngenta to analyze a highly acclaimed study examining Parkinson’s disease and pesticides done as part of the government-funded Agricultural Health Study.

That government-funded study, published in 2011 and known as the Farming and Movement Evaluation (FAME) study, reported a significant positive association between Parkinson’s and paraquat.

Publicly, Syngenta has discounted the validity of the government study, though the analysis it received essentially confirmed the FAME findings. The analysis by Mandel and Exponent said “firm conclusions cannot be drawn” about the association between paraquat and Parkinson’s, but confirmed there was a “degree of robustness” in the estimated association between paraquat exposure and risk of [Parkinson’s] in the FAME study.

The analysis was not published and instead was marked as “Attorney-Client Work Product”.  It also was not provided to the EPA.

EPA connections

Additional insights from the newly revealed records:

• Syngenta cultivated relationships with certain EPA personnel, including at least one who left the regulator to join Syngenta and lead its “FTO” or Freedom to Operate agenda. That former EPA toxicologist bragged in an internal 2017 Syngenta email that he had “been able to leverage” his EPA connections to “further our FTO interactions.”
• At one point, a Syngenta predecessor was developing a drug to treat Parkinson’s disease, spurring internal debate about the “cast-iron defence case” the company would need to make if they sold a drug to treat a disease their pesticide was suspected of causing.
• During the Obama administration, when the EPA was proposing stronger environmental regulations, including on pesticides such as Syngenta’s atrazine weedkiller, Syngenta officials appeared to take at least partial credit for spurring a political backlash against the administration and the agency. In a 2010 internal email string discussing the EPA’s “anti-agriculture actions” and resulting heavy public criticism of its actions, a Syngenta executive noted it was “‘open hunting’ season on the EPA, a good thing from our point of view.” Citing a “good turn of events”, he wrote “Well done to our team and their networks for helping to catalyze it all.”
• The company similarly spoke of targeting officials in other countries. When Brazil was moving to ban paraquat in 2017, citing the risk of Parkinson’s and concerns that the chemical may be mutagenic, Syngenta officials fretted over how to get officials to reverse course. In one email communication, a Syngenta executive wrote to other company officials that Brazil’s actions were “infuriating,” and “We need to think about getting some farmer groups wound up about this to make life uncomfortable for the [government] bureaucrats who have done this.” After a phase-out period, use in Brazil ended in 2021. Brazil’s ban came after regulators there determined evidence that Parkinson’s could be caused by paraquat was “quite consistent and reveal unacceptable risk to the human being. The use of paraquat might place the life of the workers who use it at risk.”

Bans span the globe

Sweden was among the first countries to ban paraquat, and was a key player in leading the European Union to ultimately ban the chemical across all member countries in 2007 amid concerns about neurotoxicity and Parkinson’s.

In 2011, many African countries also banned paraquat. Since then, many others have joined in blocking use of the pesticide. In all more than 70 countries have chosen to ban the chemical. In a 2022 report, the World Health Organization called for banning paraquat and certain other pesticides to reduce the risk of Parkinson’s.

One of the most noteworthy bans was made by China, not only the home to Syngenta ownership but also a large manufacturing hub for paraquat made by a range of companies and exported to the US and elsewhere.

Unlike the EPA, which largely relies on safety data that comes from the companies selling pesticides, China sought a more independent view as concerns about paraquat mounted. Deposition testimony unsealed and included in the recent court filings show that Syngenta was not happy when the Chinese government commissioned its own dermal and inhalation toxicity study at a Chinese lab.

The fact that China undertook the study without Syngenta’s knowledge was “alarming”, and the “stealth nature” of the China research on paraquat “eliminates any opportunity for Syngenta to influence the decision before it is made,” a 2015 internal company email states, according to testimony from Syngenta scientist Phil Botham in a 2024 deposition.  The EPA did not do its own such studies, Botham testified in the deposition.

China started a phase-out of paraquat in 2012 and ultimately banned it in 2016 after finding extreme toxicity risks through both routes of exposure and other health risks.  A Syngenta executive advised in another 2015 email that the company not request the study data from the Chinese government, Botham confirmed in his deposition testimony. Botham confirmed in the deposition that if the company had gained the study report, it may have had to share it with the EPA.

Even some large food companies have long ago banned paraquat in their supply chain. Dole, a global producer of fruits and vegetables, started eradicating paraquat from its fields nine years ago. A 2007 email between Syngenta executives about Dole’s decision notes a need to try to “influence” Dole’s press release on the matter “to ensure its not too damaging”.

Through it all, the US EPA has taken the position that paraquat is an important tool for farmers and evidence about serious chronic health impacts is lacking. The agency does restrict paraquat use to certified applicators and has put limits on how it can be applied to try to reduce inhalation and absorption through the skin. But the agency still allows paraquat to be sprayed from the sky on farm fields.

In its 2021 decision, the EPA said there was insufficient evidence of links between paraquat and Parkinson’s and also insufficient evidence of a range of other health problems.

The “human health database for paraquat is considered complete,” the agency said in its decision.

Several health advocacy groups challenged the EPA’s decision in court, leading the EPA to say it needed time to “further consider substantive issues.” Last November, the agency asked paraquat manufacturers to provide additional data on paraquat volatilization to help understand exposure risks to people living beyond areas where paraquat is sprayed who might be exposed.

The EPA could, in theory, do its own testing as China has done, but largely lacks the budget to do so, and under the Trump administration the EPA has largely done away with its Office of Research and Development.

Paraquat is a prime example of the weaknesses in the current regulatory system, said Ted Schettler, a former physician who serves as science director for the Science and Environmental Health Network, a group that advocates for precautionary health policies.

“This story illustrates the public health risks of allowing the US EPA to be the sole arbiter of pesticide safety,” he said. “Untold numbers of people could have been prevented from developing Parkinson’s disease, not to mention other illnesses, if the agency had done its job of protecting public health.”

[Note to readers: All the documents used as material for this story and more can be found in the TNL Paraquat Papers database.]

Featured image created by Alex Hinton.