Overview
- The study published Oct. 23, 2026 analyzed 1.86 million PFAS test records from 9,991 community water systems and generated 500 simulated estimates for each result listed as below the minimum reporting level to infer likely concentrations.
- Authors report about 98% of individual PFAS measurements in the EPA dataset were recorded as “<MRL,” and treating those results as zero made conventional summaries capture only 44% of the model’s estimated average concentration.
- For the six PFAS the EPA regulates, the model raised the national average from roughly 2.6 nanograms per liter to about 5.2 nanograms per liter, though the study does not claim to prove unsafe levels at specific sites.
- Researchers urge water agencies to publish the reporting limits and detection frequencies, provide averages that account for censored values with uncertainty, and adopt more sensitive tests to reduce hidden PFAS mass.
- Because PFAS are linked to cancers, developmental and immune harms, undercounting could mean millions face higher unrecognized exposure and could prompt changes in testing priorities, community notices, and regulatory assessments.