One Carbon or Two: EPA's PFAS Definition Fight Reaches Pesticide Aisles

Five new single-fluorinated-carbon pesticides approved by the EPA in 2024 and 2025 sit at the center of a definitional fight that will decide how millions of pounds of agricultural chemistry are regulated in the United States.

Trifludimoxazin, diflufenican, epyrifenacil, cyclobutrifluram and isocycloseram — all cleared under the current administration for use on major food crops including wheat and citrus — are PFAS under one influential definition and not under another. The Trump Administration's EPA holds that compounds with a single fluorinated carbon are not PFAS; compounds with two or more fluorinated carbons are. Critics counter that the OECD definition, which counts any compound with at least one fully fluorinated carbon atom, should govern.

The agency did not mince words in a November 2025 press release. The EPA decried "dangerous misinformation" about its pesticide approvals and stated: "EPA-approved single fluorinated compounds are NOT forever chemicals and pose no safety concerns when used according to label instructions." The pesticides, the agency added, have been "extensively studied" and are "safer than alternatives."

Whose definition counts?

The regulatory line is not about fluorine atoms. It is about how many are attached to carbon. A molecule with three fluorine atoms hanging off a single carbon has one fluorinated carbon, not three. That distinction carries the entire dispute.

The definition has shifted repeatedly. In the early 2000s these substances were known as "highly fluorinated compounds." A 2011 paper formalized a structural PFAS definition covering 268 individual compounds. The OECD expanded it in 2021 to any substance with at least one fully fluorinated carbon atom — a definition covering over 7 million compounds, with a narrower database of about 15,000.

The Biden EPA already ruled that single-fluorinated-carbon compounds are not PFAS under the Toxic Substances Control Act. The Trump EPA is extending that precedent to pesticides, blunting claims it reversed course.

The term "forever chemicals," coined in a 2018 Washington Post editorial by Harvard's Joseph G. Allen, is journalistic rather than scientific — and, strictly, inaccurate. PFOA's half-life runs about six months in soil and sediment and 2.7 years in the human body.

What does FIFRA require?

The EPA must regulate pesticides individually under the Federal Insecticide, Fungicide, and Rodenticide Act, determining whether each one causes unreasonable adverse environmental effects under common practice. Critics seeking a class-wide PFAS ban must square that demand with a statute built on chemical-by-chemical assessment.

An expert panel convened for one study largely agreed: "all PFAS" should not be grouped together, and persistence alone is insufficient for grouping in human health risk assessment. The panel found it "inappropriate to assume equal toxicity/potency across the diverse group of PFAS." The European Union takes the opposite view, regulating PFAS as a class and pushing phase-out.

The stakes are visible in the current inventory: the EPA has approved 29 herbicides, 19 insecticides and 18 fungicides that meet the OECD definition, applied to top-producing crops including corn, soybean and wheat.

How are the states moving?

More than half of U.S. states have passed laws restricting or banning PFAS-containing products, and most of those define PFAS as having "one fully fluorinated carbon atom." Maine stands alone with a pesticide-specific PFAS ban, covering pesticides with at least one fully fluorinated carbon — effective 2030. Minnesota, Colorado and New York ban PFAS products but exempt pesticides.

California rejected an outright ban on PFAS pesticides while weighing increased oversight. The agricultural industry and other opponents argue regulation should be chemical-specific. The numbers explain the pressure: an estimated 2.5 million pounds of PFAS pesticides are applied annually in California.

The benefits side of the ledger is rarely litigated. More than 107 pharmaceuticals meet the OECD definition of PFAS, and fluoropolymers — PFAS under the EPA's own definition — are components of cardiovascular stents, pacemakers and vascular grafts. In agriculture, fluorination improves pesticide stability and selectivity. One study put global crop losses to pests at 21.5 percent for wheat, 30 percent for rice, 22.5 percent for maize, 17.2 percent for potatoes and 21.4 percent for soybeans.

For the material stream, the choice of definition decides whether roughly 66 EPA-approved pesticide active ingredients and a multibillion-dollar pharmaceutical fluorination chemistry fall under PFAS controls — or stay outside them.

Maine's 2030 pesticide ban is the first hard deadline that will test which definition wins.