California cancels paraquat registration, phasing out Parkinson's-linked herbicide

Industry withdrew from California review rather than disclose risk data

California’s Department of Pesticide Regulation announced Tuesday that it had canceled the state’s last remaining paraquat pesticide registration, ending decades of agricultural use in the nation’s largest agricultural producer. The herbicide will be phased out over two years, making California the second U.S. state to prohibit the chemical after Vermont.

Paraquat has been used for decades as a powerful herbicide that can rapidly kill weeds. About 14 million pounds are sprayed annually on U.S. crops including wine grapes, pistachios, almonds, walnuts, pears, citrus, soybeans and cotton — most heavily in California’s Central Valley and the Mississippi River valley. The substance’s use tripled in the United States between 2008 and 2018 and has continued to climb, even as the chemical was already banned in more than 70 countries, including China, the United Kingdom and the European Union.

Public health advocates characterize paraquat as one of the most dangerous agricultural chemicals in commercial use. Exposure through skin contact or inhalation has been linked to death, cancer, heart failure, kidney failure, liver failure and scarring of the lungs, and there is no antidote for paraquat poisoning. The severity of the risk is reflected on an Environmental Protection Agency website titled “Paraquat Dichloride: One Sip Can Kill.” Research also shows that paraquat interferes with dopamine production and regulation, and that people with Parkinson’s disease have reduced dopamine levels — the basis for the documented link to Parkinson’s in an epidemiological study of central California farming communities exposed to paraquat and another herbicide.

California’s own preliminary review confirmed the human health concerns. The Department of Pesticide Regulation found associations between paraquat exposure and thyroid disease, reproductive harms and birth defects. The department also flagged potential risks to birds and mammals, and concluded that restrictions designed to reduce environmental exposure might not be effective because paraquat remains in the soil potentially for decades. The chemical is among the most harmful pesticides to wildlife in California, threatening at-risk species such as the San Joaquin kit fox and Swainson’s hawk.

The mechanism that produced the cancellation was a 2024 California law requiring the Department of Pesticide Regulation to re-review paraquat’s health and environmental risks. The department began requesting updated data from pesticide manufacturers. According to the department, manufacturers declined to share the requested information and instead voluntarily chose to stop using paraquat in the state. Syngenta, the Chinese-owned firm that produced the largest volume of the pesticide, withdrew its California use permit in April and announced it would stop producing the substance altogether.

“We need the right data to identify where there are risks to people and the environment,” said Karen Morrison, the Department of Pesticide Regulation’s director.

Public health advocates said the industry withdrawal was almost certainly driven by the contents of the data itself. “Paraquat is the most acutely lethal pesticide ever made,” said Nathan Donley, environmental health science director at the Center for Biological Diversity, which has for years helped lead a coalition of public-health and farmworker groups pushing for the substance’s prohibition. “I don’t think anyone thought this was going to happen this quickly, but it’s very welcome news.”

The California decision underscores a divergence with federal pesticide policy. While California moves to phase out paraquat, the Environmental Protection Agency reapproved the chemical for use in 2021 and again in 2024. Public health groups, led by the Earthjustice non-profit, have sued the EPA, charging that the agency has ignored the broad scientific consensus linking the substance to Parkinson’s disease. That lawsuit remains ongoing.

“We’re really the last major agricultural power that still uses paraquat, and we use a ton of it,” Donley said.

Donley attributed the EPA’s continued approval to industry influence at the agency and to weak federal pesticide laws. Whistleblowers have said the EPA’s pesticide division is captured by industry. Reporting in 2023 found that internal corporate documents showed Syngenta had sought to influence regulators’ decision-making around the chemical, withheld risks from the public and attempted to edit unfavorable studies. The company also maintained a “Swat team” that responded to independent reports that could interfere with its “freedom to sell” paraquat, and a significant portion of the agency’s funding comes from approving new pesticides.

“There’s just a regulatory capture there that is entrenched in the culture at the EPA, and has been for decades, and there is no desire within the agency to go against what industry wants,” Donley said.

He added: “Even if the EPA wanted to do the right thing, it’s very hard for them to do that because of the weak laws. They have to jump over a million hoops.”

California’s action is likely to add pressure on the EPA to revisit its own approval. The state’s decision follows years of advocacy from public-health and farmworker groups and comes against a global backdrop in which paraquat has already been withdrawn from agricultural use across most major economies outside the United States. The California Farm Bureau had opposed the 2024 re-evaluation law, claiming it “bypasses the scientific review process,” and signaled at the time that it would sue. No legal case has been filed.