Internal papers show Syngenta hid risks of widely used pesticide from public, regulators for decades

Nonprofit investigative news site The New Lede publishes scores of internal industry docs

Access industry documents here.

WASHINGTON – A trove of internal documents obtained and published by The New Lede show Swiss chemical giant Syngenta knew in the 1960s and 1970s that the widely used weedkiller paraquat could build up in human brain tissue and trigger effects recognized as hallmarks of Parkinson’s disease.

Although Syngenta has repeatedly claimed that scientific evidence proved its herbicide does not cause Parkinson’s disease, the internal documents contradict that external messaging. 

The documents also show that Syngenta scientists and other insiders worried as far back as the mid-1970s that the company could be exposed to legal liability over long-term, chronic effects from paraquat, including Parkinson’s disease. One company scientist called the situation “a quite terrible problem,” for which “some plan could be made….”

“Corporate cover-ups are nothing new, but it’s still shocking to see these secrets revealed about paraquat and what its manufacturers knew about the potential risks for humans,” said EWG President and Co-founder Ken Cook. “This hard-hitting, exclusive reporting is hopefully just the beginning of a much-needed process of the media holding Syngenta accountable.”

When Syngenta’s internal research showed paraquat’s harmful effects on brain tissue, it withheld that information from regulators. The company also downplayed the validity of similar findings being reported by independent scientists.

And the records show company scientists knew about evidence that exposure to paraquat could impair the central nervous system, causing tremors and other symptoms in experimental animal studies like those suffered by people with Parkinson’s disease. 

As independent researchers continued to find more evidence that paraquat may cause Parkinson’s, the documents describe what Syngenta called an “influencing” strategy “that proactively diffuses the potential threats that we face” and that helps to “maintain and safeguard paraquat registrations.” 

 The strategy “must consider how best to influence academia, and regulatory and NGO environments,” Syngenta said.

The documents show a company focused on deploying strategies to protect sales of the weedkiller, including repeatedly refuting external scientific research and working to influence regulators at the Environmental Protection Agency. 

In one defensive tactic, Syngenta executives schemed to prevent a noted independent scientist who raised questions about the safety of paraquat from sitting on an EPA advisory panel that could sway future actions by the agency to regulate or restrict use of paraquat.

Company officials did not want their efforts to block the scientist from joining the EPA panel to be traced back to Syngenta, the documents show. 

Thousands of people diagnosed with Parkinson’s are now suing Syngenta, as well as Chevron USA, the successor to a company that distributed paraquat until 1986. The New Lede, which is EWG’s independent news initiative, also ran a must-read article on paraquat users who blame Syngenta for their Parkinson’s, highlighting the chemical’s human toll.

“Whether it’s glyphosate, paraquat or any other widely used pesticide, the same story repeats on a loop – we’re told by companies these chemicals are perfectly safe, and then eventually the truth comes out on their potential harms,” said EWG’s Cook. “How many more people need to suffer because they’re being lied to about these pesticides by chemical companies?”

The full library of “Paraquat Papers” can be found here


The Environmental Working Group (EWG) is a nonprofit, non-partisan organization that empowers people to live healthier lives in a healthier environment. Through research, advocacy and unique education tools, EWG drives consumer choice and civic action.

Full disclosure: The New Lede is a journalism initiative of EWG and is a distinct service that operates independently of the organization’s advocacy and communications units. EWG has no influence on editorial decision-making at The New Lede.


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