California phasing out herbicide linked to Parkinson’s disease

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Pesticide manufacturers have voluntarily cancelled registrations for products containing paraquat in California — kickstarting a statewide phase-out of the controversial herbicide linked to Parkinson’s disease, according to a California Department of Pesticide Regulation (DPR) announcement on Monday. 

Paraquat has been under scrutiny for the last few years due to mounting scientific evidence connecting chronic exposure to the herbicide to Parkinson’s disease and other health problems. It is one of the most widely used herbicides in the US — largely as a tool to kill broadleaf weeds and grasses — and is used in growing soybeans, cotton, and corn as well as in growing grapes, pistachios, peanuts and other crops.

The California DPR began re-evaluating paraquat in 2024 and the department’s preliminary reports found negative impacts to the thyroid system, links to birth defects, and that the herbicide is harmful to wildlife, especially birds. The findings prompted the DPR to require additional studies from pesticide makers on these impacts, and, instead of providing that data, companies began cancelling their registrations beginning in April. 

“For years, communities have fought to end the use of paraquat … California will keep moving toward pest management practices that protect health and our ecosystems,” said California Secretary for Environmental Protection Yana Garcia, in a statement. 

“For years, communities have fought to end the use of paraquat … California will keep moving toward pest management practices that protect health and our ecosystems.” – Yana Garcia, California Secretary for Environmental Protection

Pesticide suppliers in the state can sell paraquat products for two years following the date of the products’ cancelled registration. DPR said the last voluntary cancellation was on August 6. 

The phase-out comes just months after Vermont became the first state to ban paraquat with some “limited exemptions.” Three other states — Pennsylvania, Michigan and New Jersey — have introduced legislation that would ban paraquat. 

And Syngenta, the key maker of paraquat for decades, announced in March that it will stop making its paraquat weed killer products and will stop selling herbicides made with paraquat by the end of June. Generic supplies of paraquat from other suppliers, however, are not impacted by Syngenta’s move.

“The writing is on the wall – paraquat is on its way out,” said Nathan Donley, environmental health science director at the Center for Biological Diversity.

Deborah Swerdlow, associate vice president of advocacy and state policy for the Parkinson’s Foundation, said the California announcement is a “significant step forward” but urged action at the federal level. 

“We don’t want someone’s protection from paraquat exposure to depend on where they live,” Swerdlow said. “We need federal action to end its use nationwide.” 

Paraquat lawsuits 

Health and environmental advocates have called for paraquat bans for years over evidence linking the herbicide — which is already banned in more than 70 countries — to Parkinson’s disease. Numerous scientific studies have found that paraquat damages cells in the brain in ways that can lead to Parkinson’s, and more than 8,000 lawsuits are pending in US courts over Parkinson’s allegations. The company has settled several cases before they went to trial and has been negotiating to settle a bulk of the ongoing cases. The New Lede reported last month that a federal judge is applying pressure to plaintiffs who are not accepting settlement agreements proposed by Syngenta.

Syngenta has long maintained that there is no credible evidence of a connection between parquat and Parkinson’s. However, internal corporate records published by The New Lede and The Guardian show Syngenta and former paraquat distributor Chevron had concerns about chronic health harms that began decades ago, but the companies never warned users.

EPA scrutiny 

Amid calls for a national ban on paraquat, in June the US Environmental Protection Agency (EPA) announced it would hold a roundtable this summer to hear from scientists, farmworkers, community advocates, and others to discuss the “documented safety challenges” associated with paraquat and explore “potential solutions and alternatives.” However, an EPA spokesperson said a date and participant list haven’t been finalized yet but that the “roundtable remains on track for this summer, as announced.” 

The EPA has not confirmed a connection between paraquat and Parkinson’s disease, but has expressed some health concerns, including paraquat’s ability to volatilize and move beyond areas where it is sprayed, potentially causing “non-occupational bystander inhalation exposure.” 

“While California and other states are taking meaningful steps to protect people from this dangerous poison, the EPA continues to spin a web of red tape to obscure paraquat’s well-documented harms,” Donley said. “The only question now is how long it will take the EPA to actually do its job and start protecting people instead of the profits of pesticide companies.”

Swerdlow said federal action could come from the EPA — or Congress could act. In June, the bipartisan Paraquat Prevention Act was introduced by House Rep. Anna Paulina Luna, a Republican from Florida, and Rep. Chellie Pingree, a Democrat from Maine.

“What we know about paraquat and Parkinson’s disease is that this is a preventable exposure and I’m encouraged to see that we have bipartisan support in Congress and we really do have momentum,” she said. 

Featured image: Elibet Valencia Muñoz/Unsplash +