SACRAMENTO, CA (MPG) – Dec. 30, the Department of Pesticide Regulation released two preliminary scientific reports following its review of human health and ecotoxicology studies on the use of the pesticide paraquat.

DPR initiated a reevaluation of paraquat in November 2024. Assembly Bill 1963, which was signed by Gov. Gavin Newsom in 2024, requires DPR to complete a reevaluation of paraquat by Jan. 1, 2029.

Paraquat is used in California to kill weeds and can only be used by professionally licensed applicators. DPR and United States Environmental Protection Agency (US EPA) have both designated paraquat as a restricted material, which means only licensed dealers may sell the pesticide and only licensed applicators may use it. In 2023 it was the 46th most used pesticide in California, with 369,978 pounds applied.

Preliminary findings

The investigative reports rely on the department’s scientific review and consideration of more than 4,000 public comments and over 150 scientific studies. DPR’s preliminary scientific evaluation found that the current registered uses of paraquat in California may adversely affect non-target organisms, including birds, mammals and aquatic organisms, with the most significant risks to birds. Additional mitigation measures, beyond restrictions on paraquat use currently in effect, may not feasibly reduce these environmental impacts to acceptable levels.

Consistent with U.S. EPA's 2019 review, DPR’s review of existing human health studies does not indicate a causal association between paraquat exposure and Parkinson’s disease. The human health preliminary report identifies a potential association between paraquat exposure and thyroid impacts and/or birth defects. The department is investigating these potential human health associations that may be linked to current paraquat uses and may require additional studies.

Public comment and next steps

DPR is opening a 45-day public comment period beginning Dec. 30 to collect input on its preliminary ecotoxicology and human health assessment scientific reports, which are available on its website. As part of the comment period, DPR is also requesting input on critical uses of paraquat and currently available, effective alternatives. The comment period will be open through Feb. 13, 2025, and comments can be submitted online or by email at [email protected].  

DPR will issue a determination on the need for any potential restrictions on paraquat after the close of the public comment period.

The department is anticipating announcing any next steps by fall 2025, including potential regulatory changes or other mitigation.

What is reevaluation?

Reevaluation is a formal process outlined in state statute to assess a pesticide’s risks, impacts or adverse effects on people and the environment. It can involve DPR requiring additional data and information from product manufacturers and evaluating the need for increasing restrictions on a product’s sales or use to mitigate potential adverse impacts on human health or the environment. If risks cannot be adequately mitigated, DPR can cancel a product’s registration.  

To view the status and timeline for DPR’s reevaluation of paraquat and other current reevaluations in progress, visit DPR’s website.