PFNA in Water

PFNA in Water: Understanding the Risks and Solutions

Introduction

Perfluorononanoic acid (PFNA) occupies an unusual position among regulated PFAS. It was included in EPA’s 2024 drinking water regulation with an enforceable limit, and it is now one of the compounds EPA has proposed to remove from that regulation. For utilities and public health officials, that makes PFNA a case study in planning against a moving regulatory target. This article covers what PFNA is, where it comes from, its health effects, its shifting regulatory status, and how it behaves in treatment.

PFNA is one of several compounds considered in our overview of PFAS health and safety.

Understanding PFNA and Its Sources

What is PFNA?

PFNA is a perfluoroalkyl carboxylic acid with a nine-carbon chain, placing it among the long-chain PFAS. That structure matters in two ways: long-chain compounds accumulate more readily in the body than short-chain ones, and they adsorb more strongly to treatment media, which makes them comparatively easier to remove.

Sources of PFNA

  • Fluoropolymer Manufacturing: PFNA has been used as a processing aid in the production of certain fluoropolymers, notably polyvinylidene fluoride. Manufacturing sites are among the most significant sources of localized contamination.

  • Aqueous Film-Forming Foams: PFNA can occur in firefighting foam formulations and at sites where they were used.

  • Degradation of Precursors: PFNA also forms from the breakdown of longer fluorotelomer compounds, meaning concentrations can rise over time without any new release.

  • Landfills and Wastewater Treatment Plants: Both act as pathways to surface water and groundwater.

Where PFNA Has Been Found

PFNA contamination in southern New Jersey, associated with fluoropolymer manufacturing, is among the most studied cases in the United States and prompted New Jersey to adopt a state drinking water standard for PFNA — the first such standard in the country. PFNA is also included in EPA’s national monitoring of unregulated contaminants, which has substantially improved knowledge of its occurrence.

Regulatory Status

The 2024 Rule

EPA’s April 2024 drinking water regulation set an enforceable maximum contaminant level for PFNA of 10 parts per trillion, and also included PFNA in a hazard index addressing mixtures of PFAS. Compliance was required by 2029.

The 2026 Proposal

In May 2026, EPA proposed rescinding the limits for PFNA, PFHxS, and HFPO-DA, together with the hazard index, while retaining the PFOA and PFOS limits with an optional extension to 2031. As of September 2026 this remains a proposal. The 2024 rule stays in effect until final action is taken, and litigation over it continues.

What This Means in Practice

Utilities should be careful not to treat rescission as settled. Three points are worth holding on to:

  • The 2024 rule remains the law until EPA finalizes a change.

  • State standards are unaffected by federal rescission. New Jersey’s PFNA standard, and any other state requirements, would continue regardless.

  • Treatment installed for PFOA and PFOS removes PFNA anyway, since it is a long-chain compound that adsorbs at least as strongly. Utilities treating for the retained compounds are unlikely to face a separate PFNA problem.

Health Effects

Research on PFNA indicates effects broadly consistent with other long-chain perfluoroalkyl acids, including liver effects, developmental effects, immune effects, and altered cholesterol levels. As a long-chain compound, PFNA is eliminated from the body slowly, so chronic low-level exposure accumulates.

Comparative toxicity across compounds is discussed in our coverage of PFAS toxicity, and the derivation of health-based values in our guide to safe PFAS levels.

Vulnerable Populations

Infants, young children, and pregnant women are generally considered more susceptible, which is reflected in how health-based values are derived.

Treatment

Conventional Treatment Does Not Work

Coagulation, sedimentation, filtration, and chlorination provide essentially no PFNA removal. A conventional treatment plant, however well run, is not a barrier to PFNA.

What Does Work

  1. Granular Activated Carbon: Effective for PFNA, which as a long-chain compound adsorbs strongly and breaks through later than shorter-chain PFAS. In mixed contamination, PFNA is rarely the compound that limits media life.

  2. PFAS-Selective Anion Exchange: Effective across chain lengths, with longer run times than carbon at shorter contact times.

  3. Reverse Osmosis and Nanofiltration: High rejection of PFNA and other PFAS, producing a concentrate stream that requires management.

What Does Not Work

Conventional advanced oxidation — ozone, UV, UV with peroxide — does not degrade PFNA or other perfluorinated acids, and can convert precursors into them. It is not a PFNA treatment.

A Practical Note on Precursors

Because PFNA forms from the degradation of longer fluorotelomer precursors, systems near fluorotelomer sources may see PFNA concentrations rise over time even after the original release has ceased. Where this is a concern, the total oxidizable precursor assay can indicate how large the precursor reservoir is.

Monitoring

PFNA is measured by liquid chromatography with tandem mass spectrometry and is included in the analyte lists of both EPA drinking water methods, 533 and 537.1, as well as Method 1633 for other matrices. Utilities monitoring for the regulated compounds will therefore have PFNA data regardless of the rescission outcome — useful information to retain, given state requirements and the possibility of future regulatory change.

Community Engagement

Shifting federal requirements are difficult to communicate. Residents who learned that PFNA was regulated may hear that the limit is being withdrawn and conclude either that the risk was overstated or that protection is being removed. Utilities are best served by explaining plainly what has changed, what has not, whether their own data shows PFNA present, and whether their treatment addresses it — which, if they are treating for PFOA and PFOS, it very likely does.

Conclusion

PFNA is a long-chain perfluoroalkyl acid associated principally with fluoropolymer manufacturing and firefighting foam, with health effects consistent with other long-chain PFAS. Its federal limit of 10 parts per trillion, set in 2024, is currently proposed for rescission, though that proposal is not final and state standards would be unaffected.

For most utilities the practical implications are modest, because PFNA adsorbs strongly and is removed by treatment installed for PFOA and PFOS. Continuing to monitor it, regardless of federal status, is sound practice — particularly where precursor degradation could drive concentrations upward. Broader questions about compounds outside the current framework are explored in our coverage of emerging PFAS compounds.