September 1, 2026.
Environmental organizations are asking the U.S. Court of Appeals for the Ninth Circuit to overturn the Trump administration’s approval of trifludimoxazin, a herbicide they say raises unresolved concerns about cancer, wildlife and long-term environmental contamination.
The petition was filed Friday by the Center for Food Safety, Center for Biological Diversity and Pesticide Action & Agroecology Network North America. The groups are challenging the U.S. Environmental Protection Agency’s June 30 registration of trifludimoxazin and six pesticide products containing the chemical.
Dispute centers on cancer evidence.
Trifludimoxazin is a broad-spectrum herbicide designed to control broadleaf and grass weeds. EPA first proposed registering the chemical in June 2025, describing it as a new tool for farmers and saying its proposed registrations were supported by human-health and ecological risk assessments. At the time, EPA said it had identified no human-health risks of concern when the chemical was used according to its label.
Environmental groups dispute that conclusion.
The Center for Food Safety says studies submitted to regulators show evidence that trifludimoxazin can cause tumors in laboratory animals. The organization argues EPA should have classified the chemical as “likely to be carcinogenic to humans,” rather than using a less stringent classification of “suggestive evidence of carcinogenic potential.”
That distinction is at the center of the legal challenge. The groups argue EPA failed to adequately account for the available scientific evidence when it authorized the pesticide.
Widely used crops could be affected.
EPA's approval allows trifludimoxazin to be used on a broad range of crops. According to the organizations challenging the registration, approved uses include corn, wheat, oats, soybeans, oranges, apples, peanuts and almonds.
The environmental organizations also characterize trifludimoxazin as a PFAS, or per- and polyfluoroalkyl substance, because of its chemical structure and the persistence of compounds produced as it breaks down.
They contend that some of the chemical's breakdown products can remain in the environment for years or decades, raising concerns about repeated agricultural applications and potential movement through soil and water.
EPA has disputed the characterization of trifludimoxazin as a PFAS under the agency's regulatory definition. The dispute is significant because PFAS chemicals are generally associated with unusual environmental persistence and have become the subject of increasing federal and state scrutiny.
Wildlife concerns.
The lawsuit also raises questions about potential impacts on wildlife and plants.
EPA's original proposed registration included an ecological risk assessment and a biological evaluation under the Endangered Species Act. EPA said that if its final evaluation determined that the pesticide could affect listed species or critical habitat, additional consultation with the U.S. Fish and Wildlife Service or National Marine Fisheries Service could be required.
Environmental organizations argue the agency's review did not adequately protect wildlife from the potential consequences of the chemical's use.
The Center for Food Safety said in July that EPA had approved several new pesticides, including trifludimoxazin, despite what the organization described as substantive scientific concerns about potential effects on human health and the environment.
EPA maintains pesticides undergo risk review.
The controversy comes as EPA continues to defend its pesticide registration process as one based on human-health and ecological assessments.
In its 2025 announcement regarding trifludimoxazin, EPA said pesticide registrations are evaluated for human-health risks and ecological effects and that restrictions or additional measures can be added if subsequent Endangered Species Act consultations identify the need for them.
The agency's position contrasts sharply with that of the organizations challenging the registration, which argue that EPA's conclusions do not adequately account for evidence they say indicates greater risks.
What happens next.
The Ninth Circuit will now have to consider the environmental organizations' challenge. The case places the federal government's pesticide-approval process under judicial scrutiny and could determine whether EPA must reconsider aspects of its review of trifludimoxazin.
The dispute also reflects a larger debate over how federal regulators should evaluate pesticides that may have persistent environmental characteristics and whether existing safety assessments adequately account for cumulative exposure, wildlife impacts and evidence from laboratory studies.
For communities that depend on clean water, healthy soils, wildlife and agricultural resources, the case could have implications beyond the individual herbicide.
The lawsuit does not establish that trifludimoxazin causes cancer in humans. Rather, the central question is whether EPA properly evaluated the available scientific evidence and complied with federal law when it approved the chemical.
Sources: U.S. Environmental Protection Agency; Center for Food Safety; Center for Biological Diversity; Courthouse News Service; Law360.
