Revealed: the undisclosed safety data emerging as weedkiller maker faces Parkinson’s lawsuits in US

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. Composite: The Guardian/Getty Images/SyngentaView image in fullscreenClues 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. Composite: The Guardian/Getty Images/SyngentaPesticidesRevealed: the undisclosed safety data emerging as weedkiller maker faces Parkinson’s lawsuits in USSyngenta 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.