MDL Judge Dismisses Four Paraquat Bellwether Cases, After Excluding Plaintiffs’ Expert Witness From Testifying at Trial

The Court determined that there were deficiencies in the experts determination that there is a causal link between Paraquat and Parkinson's disease, rendering the testimony insufficiently reliable to allow a jury to consider it at trial.

The U.S. District Judge presiding over all Paraquat Parkinson’s disease lawsuits has excluded a key expert witness from testifying at trial, leaving four individual bellwether cases without the required support to move forward to trial.

The cases are part of a massive litigation being pursued against Syngenta and Chevron, which currently includes more than 5,000 lawsuits claiming that exposure to the toxic herbicide Paraquat caused Parkinson’s disease. Each of the claims raise similar allegations that the manufacturers failed to adequately warn users about the risks associated with spraying, mixing, transporting or otherwise coming into contact with the controversial weed killer.

In support of their claims, plaintiffs have proposed a collection of expert witnesses, which will testify about the link between Paraquat and Parkinson’s, pointing to research they believe shows that exposure to the toxic herbicide may cause the progressive neurological disease. However, the manufacturers have maintained that their product is safe, and dispute the conclusions reached by many of the experts.

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Exposure to the toxic herbicide Paraquat has been linked to a risk of Parkinson's disease.

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Given common questions of fact and law raised in complaints brought by individuals nationwide, all federal Paraquat lawsuits are centralized before U.S. District Judge Nancy J. Rosenstengel in the Southern District of Illinois, as part of a federal MDL, or multidistrict litigation.

As part of the coordinated management of the litigation Judge Rosenstengel established a bellwether process, where a small group of cases have been prepared for a series of early trial dates. While the outcome of these bellwether cases does not have any binding impact on other plaintiffs, they are designed to help gauge how the court and juries may respond to certain evidence and testimony that may be repeated throughout thousands of individual claims.

Causation Expert in Paraquat Bellwether Trial Cases Dismissed

Last year, Judge Rosenstengel held Paraquat “Daubert” hearings, during which the Court considered the admissibility of proposed expert testimony in the early bellwether cases, to gauge whether the opinions offered were based on sufficiently sound and reliable science to allow a jury to consider the evidence under federal rules.

Following those hearings, defendants filed a motion calling for the exclusion of the expert testimony of Dr. Martin Wells, an epidemiologist and statistician from Cornell University, whose testimony was the key to establishing causation in at least four of the bellwether cases.

In a memorandum and order (PDF) issued on April 17, Judge Rosenstengel sided with defendants, declaring that Wells’ expert testimony should be excluded due to deficiencies in his determination that Paraquat has a causal link to Parkinson’s disease.

As Wells was the only plaintiffs’ expert witness to establish that Paraquat caused their injuries, all four of the bellwether trials were dismissed in another court order (PDF) issued that same day.

Next Steps in Paraquat Lawsuits in 2024

Following the dismissal of the initial four Paraquat bellwether cases, Judge Rosenstengel indicates that the court will move forward with a second group of claims that will go through case-specific workup, which may involve different expert testimony.

“Considering the dismissal of the four trial selection cases, the Court intends to expeditiously identify a new set of trial cases and set a tight schedule for limited discovery and trial,” Judge Rosenstengel wrote. “To that end, the Parties are DIRECTED to select 16 member cases for limited fact discovery on or before Friday, May 10, 2024.”

The order calls for plaintiffs to select eight cases, and Syngenta and Chevron to select four each for potential bellwether trials. Similar to the first bellwether pool, it is likely those selections will later be narrowed down to a smaller group that will go through expert discovery and full work up for trial.

The outcome of this ruling on the future of the Paraquat litigation is not currently known, but a number of lawyers have indicated that their cases rely on different expert witness testimony, which utilized different methods to establish the link between Paraquat and Parkinson’s disease. In addition, a large number of Paraquat cases are currently pending in various different state courts, which have different evidentiary standards for the admissibility of expert witness testimony. Therefore, unless Syngenta and Chevron are able to negotiate a global Paraquat settlement agreement in the wake of this recent ruling, they will continue to face litigation over the warnings previously provided to users of the herbicide.

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