The Regulatory History Behind PFOA/PFOS Prioritization
PFOA and PFOS were the first PFAS compounds to receive intensive scientific scrutiny. C8-related health studies, the 3M PFOS phaseout, DuPont’s Teflon contamination of the Ohio River Valley, and the landmark C8 Health Project cohort study created an enormous evidence base for these two compounds. EPA’s regulatory focus followed the science—and the science was concentrated on PFOA and PFOS for decades.
The MCL Development Process
EPA establishes MCLs based on a maximum contaminant level goal (MCLG) derived from health effects data, feasibility of treatment, analytical detection capabilities, and risk-benefit analysis. Because PFOA and PFOS had the most extensive health databases, they received the lowest MCLs (4 ng/L). The other four compounds in the 2024 rule received MCLs based on data sufficient for regulatory action but less comprehensive than the PFOA/PFOS evidence base.
Treatment Technology Drove Regulatory Design
GAC’s strong performance on PFOA and PFOS made these compounds the natural anchors for a treatment-based regulatory approach. By setting MCLs that GAC systems can reliably achieve for PFOA/PFOS, EPA designed regulations that existing and buildable infrastructure could meet. Compounds that GAC cannot reliably remove received higher MCLs (PFBS at 2,000 ng/L) or were addressed through hazard index approaches reflecting technical limitations.
What This Means for Consumers
The regulatory design efficiently addresses the best-understood and best-treatable PFAS. But consumers should understand that MCL compliance does not mean “PFAS-free water”—it means the specific regulated PFAS are below health-protective levels. The thousands of unregulated PFAS, and the regulated compounds GAC does not efficiently remove, continue to present exposure risks that standard water quality compliance does not capture.