California enacted a statewide ban on paraquat, a herbicide linked to Parkinson's disease that the state applies to more agricultural acreage than any other jurisdiction in the United States.
The pesticide, manufactured primarily by Syngenta, faces restrictions in over 70 countries. China, the United Kingdom, and the European Union prohibited it years ago. The EPA reapproved paraquat for domestic use in 2021 and again in 2024, despite mounting epidemiological evidence connecting exposure to neurological damage.
California agriculture relies on paraquat across millions of acres. The state's ban represents the most significant regulatory action against the herbicide in North America and challenges federal approval decisions that prioritize agricultural convenience over worker and community health.
The scientific case against paraquat has strengthened substantially over the past two decades. Multiple peer-reviewed studies document associations between paraquat exposure and Parkinson's disease development, particularly among farmworkers and pesticide applicators. A landmark 2011 study published in the journal Toxicology examined the mechanism by which paraquat damages dopamine-producing neurons in the brain, the cellular pathology underlying Parkinson's. Subsequent research in occupational health journals confirmed that chronic low-level exposure correlates with increased Parkinson's incidence in agricultural populations.
The EPA's 2021 reapproval decision came after the agency reviewed available toxicology data and determined that approved application methods, when followed correctly, posed acceptable risk. The agency acknowledged paraquat's neurotoxic properties but concluded that regulatory limits on use would sufficiently protect human health. Critics of that decision, including public health researchers and environmental justice advocates, contended the EPA underweighted epidemiological evidence and failed to account for real-world exposure scenarios where farmworkers and rural residents face cumulative contact.
The herbicide's continued legal status in the US contrasts sharply with international regulatory trajectories. The European Union banned paraquat in 2003 after a precautionary review. China prohibited it in 2014. The divergence reflects different regulatory philosophies. European agencies apply stricter precautionary standards, restricting substances when serious health concerns exist even without absolute proof of causation. The EPA typically requires stronger causal evidence before restricting commercial chemicals.
California's action follows the state's established pattern of setting pesticide standards stricter than federal baselines. The state's Department of Pesticide Regulation initiated the paraquat review process in 2020 and completed its assessment by 2024. The ban takes effect in phases, giving agricultural operations time to transition to alternative herbicides.
Syngenta and agricultural organizations representing conventional farmers have opposed the ban, arguing that paraquat remains essential for certain weed control applications and that alternatives carry their own agronomic limitations. Farm representatives note that the herbicide's rapid action and reliability make it economically valuable for large-scale commodity crops.
California's decision will likely intensify federal-level pressure on the EPA to revisit paraquat approval. Several states have initiated their own reviews. Advocacy groups including the Pesticide Action Network have called on the EPA to align domestic policy with international precedent. Litigation over paraquat's health effects continues in federal courts, with farmworker plaintiffs seeking damages for Parkinson's disease they attribute to occupational exposure.
The ban affects an estimated seven million acres under cultivation in California. Growers will need to adopt alternatives such as glyphosate, glufosinate, or mechanical weed control methods.