Chemical giant Syngenta worked to manipulate connections between weed killer paraquat and Parkinson’s disease, according to an investigation by The Guardian.

In a lengthy article published in early June, the news agency said it reviewed a trove of internal corporate documents that show the many ways Syngenta worked to protect its product and distance it from the health risks of paraquat.

The popular weed killer, branded as Gramoxone, has been used on American crops since the 1960s. Numerous scientific studies have tied the toxic chemical to increased occurrences of Parkinson’s disease in farmers and agricultural workers.

Syngenta has long worked to discredit the connection, calling evidence linking paraquat to Parkinson’s disease “fragmentary and inconclusive,” The Guardian reported. But internal corporate documents reviewed by the news outlet outline how Syngenta worked to “secretly influence scientific research regarding links between its top-selling weed killer and Parkinson’s,” according to the news report. 

Internal Files Reveal Strategies

The files exposed various tactics the company took, including involving a well-known U.K. scientist and other researchers who authored scientific literature without disclosing their connection to the company, The Guardian reported. This included withholding unfavorable research findings from regulators and employing lawyers to downplay concerning scientific reports by suggesting edits.

An unnamed company spokesperson told The Guardian Syngenta cares about making its products safe for use and downplayed research that connected paraquat to Parkinson’s disease.

“We care deeply about the health and wellbeing of farmers and are dedicated to providing them safe and effective products. As a responsible company, we have spent millions of dollars on testing our products to make them safe for their intended use,” the spokesperson told The Guardian.

The Syngenta spokesperson further said of the more than 1,200 studies of paraquat, none have “established a causal connection between paraquat and Parkinson’s disease.”

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Paraquat Banned in More Than 30 Countries

American farmers use paraquat on dozens of commercially grown crops, including soybeans and corn, to kill weeds and grass. While the herbicide works well at destroying unwanted plants, more than 30 countries have banned the chemical because of its toxicity to humans.

The U.S. Environmental Protection Agency warned that the toxic pesticide is so harmful to humans that “one sip can kill.” It can be easily mixed in water, food or other beverages, but in order to prevent accidental ingestion it contains dyes, odors and vomiting agents. Because of the dangers, the EPA has said only licensed, trained applicators are allowed to handle the toxic chemical. Those workers can be put at risk of exposure.

Agricultural workers such as farmers, growers, pickers and others can be at risk of paraquat exposure. Paraquat poisoning through ingestion, inhalation or skin exposure can lead to serious health problems, including death. 

Paraquat lawsuits have been filed that claim manufacturers knew about the risks associated with paraquat but failed to warn the public. 

There is no official stance on paraquat’s link to Parkinson’s disease from the EPA or the Centers for Disease Control and Prevention. However, a study by the Unified Parkinson’s Advocacy Council found that people exposed to paraquat in their teen or young adult years had an increased Parkinson’s risk of 200% to 600%.