A California lawmaker is pressing to ban the pesticide paraquat despite a federal judge’s recent conclusion in several civil lawsuits that expert witness testimony had failed to prove the chemical causes Parkinson’s disease.
Assemblywoman Laura Friedman (D-Burbank) has introduced legislation, Assembly Bill 1963, that would phase out the use of paraquat in California by January 2026. Friedman argues that the pesticide, a weed killer with links to both Parkinson’s and childhood leukemia, is widely used in the Central Valley and poses risks to many largely Latino communities.
“The evidence is clear: Paraquat poses a serious risk to human health and the environment,” Friedman said earlier this year in a prepared statement. “With more than 60 countries already banning its use, it's time for California to follow suit to protect Californians, especially those in poor, rural communities, from exposure to this toxic weed killer.”
Also supporting Friedman’s legislation is the nonprofit Environmental Working Group (EWG). Neither the assemblywoman’s office nor EWG would comment on the recent decision in the paraquat multi-district litigation in Illinois, in which Judge Nancy Rosenstengel concluded that four cases alleging occupational exposure to paraquat resulting in Parkinson’s disease were based on expert testimony containing flawed methodology and pre-determined results. Those cases have been dismissed
But an EWG spokeswoman told the Southern California Record that the link between paraquat and Parkinson’s is well-established. She pointed to UCLA research published earlier this year that concluded people working near intense paraquat-spraying locations in the Central Valley were more likely to develop Parkinson’s than the general population.
In addition, a 2019 meta-analysis indicated that both occupational and environmental exposure to the pesticide increased risks of Parkinson’s by 64%, EWG reports.
Syngenta, the Swiss-based company that is the main manufacturer of paraquat, argues that claims of a causal link between the chemical and Parkinson’s are not supported by scientific evidence.
A company spokesman said in an email that paraquat plays an important role in California agriculture because it quickly controls damaging weeds, preserves crop roots and does not adversely affect “soil microbes, microorganisms and earthworms.”
“AB 1963 relies upon unsubstantiated and unscientific claims,” spokesman Saswato Das told the Record. “Such claims have been rejected by the U.S. (Environmental Protection Agency), the Joint Meeting on Pesticides Residues (JMPR) of the Food and Agricultural Organization (FAO) and World Health Organization (WHO), the Australian Pesticides and Veterinary Medicines Authority (APVMA) and other high-quality independent studies. The hypothesis that paraquat causes Parkinson’s is not, and has never been, accepted in the medical community or by peer-reviewed science.”
In addition, California tightly regulates the pesticide to ensure its safe use, since it can only legally be applied by state-certified individuals, according to Das.
In the multi-district litigation, which involves more than 5,000 plaintiffs who alleged they developed Parkinson’s due to paraquat exposure, a plaintiffs’ expert witness concluded that his meta-analysis of epidemiological studies established a 2.8-to-1 elevated risk of the disease from occupational exposure from the chemical.
But the Illinois judge concluded that professor Martin Wells’ conclusions about causation resulted from a predetermined result and were likely the product of “cooking the books” and scientific cherry-picking.
“... The odds ratio of 2.8 is the product of numerous methodological defects that strongly undermine its reliability,” Rosenstengel concluded in her 97-page order. “Accordingly, Dr. Wells’ reliance on this odds ratio to support his conclusion of a strong association between occupational paraquat exposure and Parkinson’s disease is problematic in and of itself. Indeed, even his reliance on his meta-analysis appears to overlook the fact that five of the seven studies in it yielded a statistically insignificant result.”
The judge concluded that Wells’ opinions are not admissible under Federal Rule of Evidence and the Daubert legal standard and must be excluded.
Friedman’s bill passed the state Assembly in May and is now being scrutinized by Senate committees.
Tort reform advocates have cast doubt on numerous scientific theories raised during civil court proceedings in recent years, equating them to "junk science."