Syngenta denies keeping relevant data from the EPA as paraquat stays in the US market despite global bans

Sweden started ringing the alarm bell more than 20 years ago, calling for a ban on the weedkilling chemical paraquat in 2004. One by one, dozens of other countries did the same as evidence of paraquat risks to human health mounted. Even the Chinese government, which owns the longtime paraquat maker Syngenta, halted domestic use of the pesticide a decade ago after conducting its own studies on paraquat safety and finding troubling results.

In the US, two states – Vermont and California – have recently also banned paraquat, citing risks that include an association between paraquat and Parkinson’s disease shown in years of scientific research. And California regulators announced in August that paraquat makers voluntarily agreed to stop selling the chemical after the state identified health concerns in connection with its use 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 scientific findings linking paraquat to Parkinson’s, an incurable brain disease. The agency said in June it would hold a round table over the summer to re-examine the “safety challenges” associated with paraquat. But no such event has yet been held or 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, a Swiss-headquartered multinational, fought to keep a tight hold on the US market, where use of paraquat nearly tripled between 2000 and 2018, a time period when dozens of other countries were banning paraquat.

Internal corporate records, depositions and other records show that 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 untreated clothing; how fast it could absorb into an applicator’s skin and bloodstream. The company also did not share some information about how mixing paraquat with surfactants increases the chemical’s absorption. Surfactants are additives commonly used by farm workers to help herbicides overcome the waxy, water-repellent surface of their leaves. Certain information demonstrating dire risks to the brain from exposure was also not shared with the EPA.

In contrast, the company focused on developing and promoting science showing paraquat safety that it could share with regulators, including one 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” weedkiller 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 share with the EPA. The records were submitted to a Pennsylvania state court where cases have been filed by people with Parkinson’s alleging that they developed the disease from exposure to paraquat products. Earlier this month the underlying lawsuit in which the documents were filed was dismissed by the judge due to the plaintiff not having sufficient proof of exposure to paraquat; however, there are thousands more active cases pending around the country.

In the face of the ongoing litigation, which has already cost the company at least $187m 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.

Asked about the newly disclosed US court documents, Syngenta said it has never knowingly failed to provide regulators with any relevant and required information. The company has long maintained that there is no actual link between paraquat and Parkinson’s disease, and that its decision to stop selling was purely based on market factors. The settlements include no admission of liability.

Other suppliers continue to sell in the US as the EPA maintains 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 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 that the company failed to share certain data with the EPA are particularly concerning now, coming just months after the US supreme court issued a ruling declaring the EPA as the pre-emptive authority for determining when a pesticide product needs to include a particular health warning.

“When the pesticides 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, a professor of epidemiology and population health at the Stanford University School of Medicine.

When asked about Woodruff’s comment, Syngenta rejected the claims and said it takes the safety of its products very seriously.

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 noted that the paraquat review is ongoing.

“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 federal agency said.

The agency said that companies must submit information “regarding any unexpected or unreasonable adverse effects resulting from their product’s use to EPA. Failure to comply is a direct violation of federal law,” the agency said.

‘Bad news’

The key law regulating pesticides – including herbicides – the Federal Insecticide, Fungicide and Rodenticide Act (Fifra), 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 Syngenta acknowledged in discovery 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 by the New Lede and the Guardian about numerous 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”.

There are many examples of information that Syngenta developed or accessed but did not give to the EPA, according to the court documents and internal company files. Here are a few:

• Information about concerns with surfactants, which farm workers mix into weedkillers to help absorption on plants. Labels on the company’s US products have long recommended that users add surfactants prior to spraying paraquat to make it more effective. But at least since the 1970s, the company has had information that paraquat could become more toxic when mixed with surfactants. Company files show worries about “increased toxicity” when surfactants were added to paraquat and include studies showing the potential for increased absorption, including through skin and nasal membranes. The company did not share at least some of those findings with the EPA, 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 when asked about the surfactant concerns that Syngenta conducted many studies that found no harmful effects on the nervous system. The surfactant used in Syngenta’s Gramoxone product was “specifically selected not to accelerate epidermal penetration”, the spokesperson said. The company additionally said numerous studies show surfactants have “no significant impact on dermal absorption of paraquat”.


• Data showing that Syngenta’s Gramoxone paraquat product “almost immediately” penetrated cotton and other clothing materials, including Tyvek materials commonly used in protective apparel. Though the study was done in 1985, Gramoxone labels have stated for years that users can wear a “long-sleeved shirt and long pants”. When asked about why the study results were not given to the EPA, Syngenta said that the product was not registered in the US, the results only confirmed information already known, and labels at that time in the US already recommended waterproof footwear and clothing.


• 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”. When asked about the analysis, the company said the situation was not relevant to the use of paraquat products in the US for various reasons, including the fact that the US required personal protective equipment.


• 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 email in June 2007. When asked about the evaluation, Syngenta said most paraquat absorbed into the body is rapidly excreted through urine and so is not a “regulatory or toxicological concern”. The company also said that the AOEL data involved operators who were not complying with paraquat safety measures, and the company said the high exposures were “not representative of normal paraquat use”.

In its defense, Syngenta notes in the same court filing 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. It also said that EPA guidance regarding company requirements under the Federal Insecticide, Fungicide and Rodenticide Act had “evolved”, and the company had 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”.

‘Brush aside 10 years of research’

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. Farmers have 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 the disease and its weedkiller.

But numerous scientific studies have found that paraquat damages cells in the brain in ways that can lead to Parkinson’s. Concerns accelerated in the 2000s as several researchers published studies supporting such a link.

By 2003 the company was noting the rising external pressure on paraquat and 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.