Perfluorononanoic acid (PFNA) is a 9-carbon chain PFAS compound that has emerged as a significant contaminant in drinking water supplies, particularly in areas with historical manufacturing activity. Regulated under EPA’s 2024 PFAS rule at 4 ppt, PFNA is among the most bioaccumulative PFAS compounds and warrants dedicated attention in filter selection.
PFNA’s Physical Properties and Filtration
With a longer chain than PFOA, PFNA exhibits even stronger hydrophobic character and higher binding affinity for activated carbon surfaces. This makes PFNA one of the more readily removed PFAS by carbon-based filtration. Studies confirm that high-quality activated carbon block filters achieve PFNA removal rates exceeding 97% under standard conditions, and RO systems consistently remove 98% or more.
Occurrence and Monitoring
PFNA has been detected in water supplies associated with fluorochemical manufacturing facilities and downstream river systems. Some communities have historically relied on drinking water sources with PFNA as the dominant detected PFAS, making it the driver of treatment system design. For these communities, carbon filtration or RO provides reliable protection given PFNA’s favorable adsorption characteristics.
Filter Selection for PFNA
For households with detected PFNA, any filter certified to NSF/ANSI 53 for PFAS reduction or NSF/ANSI 58 for RO systems should provide effective removal. Since PFNA behaves similarly to PFOA in adsorption studies, PFOA-certified filter performance data is a reasonable proxy for expected PFNA removal efficiency. Annual post-filter testing confirms continued performance.