PFAS Is Not One Chemical—It Is a Family of Thousands
Public discourse about PFAS often implicitly equates the entire class with PFOA and PFOS, the two compounds that first gained widespread attention. But PFAS (per- and polyfluoroalkyl substances) is a class of over 4,700 distinct chemical compounds, each with different physical properties, environmental behavior, biological effects, and—critically—different responses to water treatment technologies.
The Regulatory Focus on a Tiny Fraction
EPA’s current MCL rule covers six PFAS compounds: PFOA, PFOS, PFNA, PFHxS, HFPO-DA, and PFBS. Six compounds out of 4,700+. While these six were selected based on available health data and environmental prevalence, the choice simultaneously creates the impression that water meeting MCLs for these compounds is “PFAS-safe.” This is a profound mischaracterization.
GAC Treatment for Six vs. 4,700 Compounds
Activated carbon systems are designed, sized, and operated to achieve compliance with specific regulated compounds—primarily PFOA and PFOS. Carbon bed replacement schedules, EBCT designs, and performance guarantees are based on these target compounds. The filter’s performance on the other 4,694+ PFAS compounds is simply unknown for most utilities and largely unmonitored.
The Known Unknown of Unmonitored PFAS
Several utility-scale studies that tested for expanded PFAS panels (50–100 compounds) found that many unregulated PFAS remained in finished water after GAC treatment at concentrations equaling or exceeding the regulated PFAS concentrations. Consumers receiving “compliant” water may still be receiving a complex cocktail of unmonitored PFAS that current treatment technology cannot address.