California Bans Paraquat Herbicide Linked to Parkinson’s Disease

California is systematically phasing out paraquat dichloride following a series of regulatory pressures and a major chemical spill, making the nation’s largest user of the controversial herbicide move toward a complete prohibition by 2029, according to state environmental records. The transition away from the weedkiller unfolds as chemical manufacturers voluntarily cancel their state product registrations rather than submit required health toxicology data mandated by state legislation.

The Regulatory Path From AB 1963 to Voluntary Cancellation

The state’s Department of Pesticide Regulation announced that every pesticide manufacturing company utilizing paraquat in California voluntarily canceled its state product registrations by August 2026. This administrative milestone follows the September 2024 passage of Assembly Bill 1963, a law that required the department to thoroughly evaluate the health and environmental risks tied to heavy agricultural usage across the state, particularly within the San Joaquin Valley.

According to the Department of Pesticide Regulation, officials required registration holders to submit comprehensive scientific data by June 5, 2026, to address critical gaps in the human health toxicology database. Rather than providing this data, manufacturers began dropping their product registrations in April 2026. The final cancellation took effect on August 6, 2026. Under state rules, licensed dealers may continue to possess and sell previously registered supplies for up to two years following a cancellation date, leading up to the final 2029 phase-out deadline mandated by state oversight.

Public Health Concerns and Neurological Risks

Public health advocates have long characterized paraquat as a high-risk substance. According to statements from the Environmental Working Group, the weedkiller is linked to Parkinson’s disease, thyroid disease, childhood leukemia, non-Hodgkin lymphoma, and birth defects. The Pesticide Action and Agroecology Network similarly notes that the chemical poses severe risks to the heart, liver, kidneys, and lungs, while also carrying associations with amyotrophic lateral sclerosis (ALS).

These clinical concerns run parallel to international regulatory actions. Paraquat is already outlawed in more than 70 countries, including the United Kingdom, China, and member states of the European Union. Despite these international prohibitions, the U.S. Environmental Protection Agency reapproved the chemical’s registration in 2021 and subsequently declined to alter its stance following legal challenges and scientific petitions from groups referencing neurological safety data.

The Dorris Chemical Spill Catalyst

While the state’s reevaluation process began years prior, public and political urgency intensified following an industrial accident in the rural Northern California town of Dorris. On March 17, 2026, a 140-gallon tank containing concentrated paraquat—transported by Macy’s Flying Service—rolled off a truck bed and spilled approximately 50 gallons onto Highway 97.

The incident prompted the Siskiyou County Sheriff’s Office and the California Highway Patrol to shut down the town of roughly 800 residents under an emergency shelter-in-place order. Emergency response teams spent the day containing the spill on the roadway and shoulder, sparking immediate outcry from environmental and healthcare lobbyists who pressed for swift regulatory intervention against the herbicide.

National Supply Chains and Future Medical Oversight

Globally, the supply chain remains anchored by major chemical producers. SinoChem, which purchased Syngenta, operates as the world’s leading manufacturer of paraquat and continues to import tens of millions of pounds into the United States annually. However, industry shifts are occurring independently; Syngenta announced the end of its own production cycles due to competition from generic brands, creating additional disruption in domestic agricultural markets.

For agricultural workers, rural communities, and patients managing complex neurodegenerative conditions or occupational exposures, navigating these shifting chemical environments requires rigorous clinical monitoring.

California Secretary for Environmental Protection Yana Garcia noted in the state’s announcement that the region will continue its trajectory toward agricultural pest management practices designed to safeguard human health and local ecosystems.

Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.