On August 18, 2026, the U.S. Court of Appeals for the D.C. Circuit upheld EPA’s 2024 rule designating two widely used per- and polyfluoroalkyl substances (PFAS), perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), as “hazardous substances” under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

EPA issued the final rule in April 2024, which became effective in July 2024. The designation enables EPA to investigate and compel or undertake cleanups of properties with PFOA and PFOS contamination and allows EPA and other parties that incur response costs in investigating and remediating these substances to seek cost recovery or contribution from other potentially responsible parties. As explained in a prior SPR blog post, the listing also makes these substances subject to federal reporting requirements and requires that owners or operators of vessels or facilities provide notice of certain releases of them.

In June 2024, the U.S. Chamber of Commerce and other trade associations challenged the rule and EPA’s underlying rationale in the D.C. Circuit. After the Trump administration took office in January 2025, the litigation was held in abeyance while EPA reviewed the rule. In September 2025, EPA ultimately announced that it would retain the rule.

The D.C. Circuit heard argument in the case in January 2026, and a panel of the Court of Appeals issued its unanimous decision upholding the “hazardous substances” designation on August 18, 2026.

Petitioners raised three principal arguments:

• EPA misinterpreted the statutory language “may present substantial danger” in CERCLA’s definition of a hazardous substance;
• EPA’s cost-benefit analysis provided insufficient notice to the parties; and
• EPA’s cost-benefit analysis and decision to regulate in the face of uncertainty were arbitrary and capricious.

Statutory Interpretation Questions

Petitioners argued that EPA’s designation of a hazardous substance requires the agency to find that substantial danger “will” occur upon release. The D.C. Circuit disagreed. It explained that the plain statutory text provides that EPA shall designate hazardous substances as those “elements, compounds, mixtures, solutions, and substances which, when released into the environment, may present substantial danger to the public health or welfare or the environment” and that the plain meaning of “may” denotes contingency—consistent with EPA’s interpretation that “may” means “scientifically possible” and that it need not have certainty of the danger. Requiring absolute scientific certainty as to the consequences of every single release, the Court noted, would “legislatively paralyze” the statute. In the Court’s view, the statute’s requirement that a release may present “substantial danger” to public health, welfare, or the environment sufficiently cabins EPA’s designation, dispensing with Petitioners’ suggestion that table salt could be characterized as a hazardous substance under EPA’s test.

The Court also underscored that Petitioners did not—and indeed, could not—plausibly dispute that PFOA and PFOS qualify as substances that may pose a substantial risk to public health, welfare, and the environment if released, as evidenced in peer-reviewed studies linking PFOA and PFOS exposure to a number of health conditions.

The Court readily rejected Petitioners’ other arguments, including allegations that EPA’s interpretation of the statute raised concerns under the nondelegation and void-for-vagueness doctrines, noting among other things that Congress had set forth a clear “general policy” for EPA to “regulat[e] substances that are particularly harmful to humans and the environment by creating a cleanup and cost-allocation scheme that puts the onus on polluters rather than taxpayers” and that Petitioners were afforded ample notice and opportunity to voice their concerns through the notice-and-comment rulemaking process.

APA Claims

With respect to their APA claims, Petitioners argued that EPA impermissibly relied on a regulatory impact analysis that was not disclosed until issuance of the final rule. The Court dispensed with this claim, finding that the regulatory impact analysis was a “logical outgrowth” of the cost-benefit analysis that had been provided with the notice of proposed rulemaking, which specifically solicited comments on the scope of the cost-benefit analysis. Additionally, the new cost data contained in the regulatory impact analysis—which were in part a response to Petitioners’ own comments—were not “‘critical’ to the final decision.”

The Court also rejected Petitioners’ argument that the cost-benefit analysis was arbitrary and capricious because, in their view, EPA (1) miscalculated cleanup costs at sites on the National Priorities List, (2) miscalculated costs at sites off of the National Priorities List, (3) ignored cleanup costs at federal sites, (4) disregarded the impact on certain industries, (5) incorrectly assessed benefits, and (6) failed to consider the impact of the Designation on small businesses. The Court noted that EPA is entitled to “significant deference” with respect to highly technical issues and further determined that EPA’s conclusions were reasonable and supported by the record, even if Petitioners may have desired a different approach.

Nor was the Court persuaded by Petitioners’ argument that uncertainty regarding contamination, costs, future liability, and real estate transactions in connection with PFOA and PFOS rendered EPA’s designation improper. The Court emphasized that EPA acknowledged these uncertainties, but that CERCLA actions were “discretionary, contingent, and site specific” and included an evaluation of the relative risks and benefits.

Impact

The D.C. Circuit’s ruling not only upheld EPA’s designation of PFOA and PFOS as CERCLA hazardous substances, but reaffirmed EPA’s authority to act on credible scientific evidence of risk without definitive proof of harm. The decision is also a notable early illustration of courts’ treatment of agency rulemaking under the post-Loper Bright framework. The Court did not defer to EPA’s statutory interpretation of CERCLA—as it would have under the Chevron doctrine—but instead independently determined the “best reading of the statute as a matter of text and context.” However, the Court largely deferred to EPA’s scientific findings and technical evaluations.

The designation upheld by the court has the potential to impact businesses in a variety of sectors. EPA could expand active investigations or re-open closed sites where PFOS or PFOA may be present and could require removals based solely on the presence of these compounds. This designation also allows EPA and potentially responsible parties to institute CERCLA litigations to recover costs related to PFOS or PFOA and serves as a predicate to natural resource damage claims under CERCLA.

The decision further underscores the importance of due diligence in real property transactions and serves as a reminder to businesses to evaluate how these designations affect compliance and risk management. Additional considerations have been discussed in greater detail in our prior post.

The SPR Blog will continue to provide updates and analysis of significant legal developments and litigation involving PFAS.