On August 14, 2019, the California Department of Pesticide Regulation (DPR) issued cancellation notices to thirteen California registrants of pesticide products containing chlorpyrifos, including Dow Agrosciences LLC (now Corteva).  Each of these notices is referred to as an "Accusation," and each affected registrant has 15 days to request a hearing concerning the proposed cancellation.  DPR's issuance of these notices followed a final decision by the U.S. Environmental Protection Agency (EPA) to deny an administrative petition to revoke the tolerances and cancel the U.S. registrations for chlorpyrifos.  DPR states: "Despite the Trump administration's reversal of a decision to ban the pesticide at the federal level, California continues to move forward to protect public health, workers, and the environment."  Although it is unusual for a State to act unilaterally to cancel a State registration for a pesticide that is still registered under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), FIFRA Section 24(a) provides that States may separately regulate Federally registered pesticides so long as they do not purport to authorize any sale or use that is otherwise prohibited under FIFRA.

The risk assessment that supports DPR's proposal to cancel chlorpyrifos products is based on five animal studies published in 2016, 2017, and 2018, that report neurotoxicity from chlorpyrifos at exposure levels that are considerably lower than the levels that cause acetylcholinesterase inhibition.  Based on its evaluation these studies, DPR has concluded that developmental neurotoxicity is the critical endpoint for chlorpyrifos and has derived a point of departure for chlorpyrifos risk assessment.  Based on this assessment, DPR previously concluded that chlorpyrifos should be designated as a Toxic Air Contaminant (TAC).  DPR presented its TAC findings to California's Scientific Review Panel at a meeting on July 30, 2018, and the Panel subsequently concluded that the DPR assessment of the developmental neurotoxicity of chlorpyrifos was "based on sound scientific knowledge, and represents a balanced assessment of our current scientific understanding."

On the same day DPR issued its cancellation notices for chlorpyrifos, DPR also announced it has established an Alternatives to Chlorpyrifos Work Group with experts from "agriculture, California universities, environmental justice groups, farmworker health and safety organizations, and pesticide manufacturers…"  DPR has asked this Work Group to develop short-term practical alternatives to chlorpyrifos, along with a five-year action plan.  The Work Group is supposed to conclude its work by the spring of 2020.  The budget for 2019-2020 approved by the California Legislature also includes $5 million in grant funding to develop sustainable alternatives to chlorpyrifos.

Commentary

The DPR decision to cancel chlorpyrifos relies primarily on new animal studies that report that chlorpyrifos causes neurodevelopmental effects at levels that are well below those that inhibit cholinesterase.  DPR refers in passing to the epidemiology studies for chlorpyrifos that EPA used to make its Food Quality Protection Act (FQPA) determination for all organophosphate (OP) pesticides, but these data were not used by DPR to derive its point of departure for chlorpyrifos risk assessment.

EPA scientists have not yet prepared a formal evaluation of the new animal studies for chlorpyrifos, but EPA's decision to deny the petition to revoke tolerances and cancel registrations for chlorpyrifos states that EPA intends to evaluate the new animal studies as part of its registration review deliberations for chlorpyrifos.  The FIFRA registrations for chlorpyrifos may also be affected by pending judicial actions challenging EPA's decision to deny the petition to revoke the tolerances and cancel the registrations for chlorpyrifos.  In this complicated environment, it will be important to monitor the registrants’ and industry’s response to DPR's cancellation actions, as well as their efforts on the pending Federal court litigation and EPA's registration review process for chlorpyrifos.