Judge rejects key expert in paraquat lawsuits, tosses first cases set for trial

A key expert witness in lawsuits claiming that Syngenta's herbicide paraquat causes Parkinson's disease cannot testify in court, a federal judge ruled Wednesday, dismissing the first four cases over the product that were set to go to trial.

Lawyers for agricultural workers suing Syngenta and Chevron (CVX.N), opens new tab, which sold paraquat before 1986, had sought to have Cornell University professor Martin Wells testify that occupational exposure to the chemical can cause the disease. Without that testimony, U.S. District Judge Nancy Rosenstengel found, the trials cannot go forward.

Rosenstengel's ruling does not apply directly to the more than 5,000 other cases centralized in her court in East St. Louis, Illinois. She ordered the plaintiffs' lawyers and the companies to propose another set of cases for trial, which will give the plaintiffs a chance to offer a new expert.

Rosenstengel, in barring Wells from testifying, opens new tab, said his analysis of the data relied on "unscientific cherry-picking." She also said it was a "red flag" that his view "has not been adopted or independently validated in any peer-reviewed scientific analysis outside of this litigation."

Lead attorneys for plaintiffs in the litigation — Khaldoun Baghdadi of Walkup, Melodia, Kelly & Schoenberger; Sarah Doles of Levin, Papantonio, Rafferty, Proctor, Buchanan, O'Brien; and Peter Flowers of Meyers & Flowers — said in a joint statement that they disagreed with the ruling and would appeal it, and that they looked forward to taking a new set of cases to trial.

"We will continue to prosecute these cases on behalf of the thousands of American farmworkers diagnosed with an incurable and debilitating disease because of their exposure to paraquat," they said.

The companies have denied that paraquat causes Parkinson's, a progressive nervous system disease that causes tremors and difficulty moving.

Chevron said in a statement that the decision affirmed that "despite hundreds of studies conducted over the past 60 years, the scientific consensus is that paraquat has not been shown to be a cause of Parkinson's disease."

A Syngenta spokesperson said the company was pleased with the ruling, which it called "consistent with decades of peer-reviewed scientific literature."

Several hundred paraquat cases are also pending in state courts, most in California. The first state court trials could happen later this year.

The paraquat litigation was, for a time, the most heavily advertised mass tort litigation by plaintiffs' lawyers. Cases were centralized before Rosenstengel in June 2021.

Paraquat has been on the market since the mid-1960s but has been banned in more than 60 countries. It is approved by the U.S. Environmental Protection Agency only for licensed users, often on large commercial farms.

The herbicide is currently marketed in the U.S. by Syngenta under the brand name Gramoxone. It has remained popular partly thanks to weeds becoming resistant to Bayer's Roundup, which is at the center of a separate mass tort litigation.

Syngenta is a subsidiary of Sinochem, a Chinese state-owned company.

The case is In re: Paraquat Products Liability Litigation, U.S. District Court for the Southern District of Illinois, No. 3:21-md-3004.