EPA may miss over half of PFAS in water

The study, published in Cell Reports Sustainability, found that the EPA’s latest reports capture only 44% of the average combined concentration of 25 PFAS in U.S. water systems. The researchers used computer modeling to estimate concentrations that are normally treated as zero when results fall below the EPA’s minimum reporting levels. PFAS, or “forever chemicals,” can persist in the environment and are linked to cancers, high cholesterol and reproductive problems.

How the study estimates hidden PFAS

The analysis drew on more than 1.8 million PFAS measurement records from the EPA’s January 2026 release of the Fifth Unregulated Contaminant Monitoring Rule. The data cover 9,991 community water systems. Of the records, 98% fall below the minimum reporting limit, a threshold that most laboratories can reliably measure. By averaging hundreds of data points and applying a statistical model, the authors estimated the likely concentrations for these below‑limit results. These are model predictions rather than measured concentrations.

Because a result below the reporting limit does not mean zero, the study argues that current EPA summaries underestimate exposure. Researchers such as Jesse Goodrich at the University of Southern California explain that trace contamination can accumulate over time, contributing to the ubiquitous PFAS levels seen in human blood. The team has released PFAS‑CAST, an open‑source tool designed to let agencies explore this approach with their own monitoring data.

The findings arrive amid concern from scientists about the EPA’s proposal, in May, to drop limits for four cancer‑linked PFAS chemicals, and after a separate report found that more than 80% of tested U.S. waterways were polluted. Advocates say that conservative treatment of unmeasurable samples can mask real exposure, and that better estimation methods should be used.