TCU Research Finds Drinking Water May Contain More ‘Forever Chemicals’ Than Standard Reports Suggest
A new study led by Texas Christian University researcher Gehendra Kharel suggests that common methods for reporting harmful substances in U.S. drinking water may significantly underestimate the amounts of the chemicals present. Common ways of reporting per- and polyfluoroalkyl substances (PFAS), the man-made “forever chemicals” that persist in the environment and have been linked to health problems, could understate their estimated concentration by roughly half, finds the study, published Oct. 23 in the Cell Press journal Cell Reports Sustainability.
“When the levels of these chemicals are below our reporting limit, it’s often treated as zero when we calculate how widespread they are,” said Kharel, first author of the study and associate professor of environmental and geological sciences in the Louise Dilworth Davis College of Science & Engineering. “We set out to understand how treating those results as zero changes the picture of PFAS occurrence in drinking water.”
Kharel and his coauthors, Omar Harvey of TCU, Andrei P. Kirilenko of the University of Florida and Chris B. Zou of Oklahoma State University, examined more than 1.8 million PFAS measurements from a national Environmental Protection Agency dataset. About 98% of the test results fell below minimum reporting levels. Using statistical models to estimate possible concentrations for those results, the researchers found that treating them as zero captured only 44% of the estimated average concentration of 25 PFAS across 9,991 community water systems under the study’s primary model. The averages give more weight to systems that serve more people.
The findings do not mean that every result below a reporting limit represents a health risk, or that any water system is unsafe or out of compliance with drinking-water standards. Instead, Kharel said the study addresses how PFAS measurements are summarized and could help water agencies better account for uncertainty in monitoring data.
“When a water quality report says ‘not detected,’ that means below the reporting limit, not zero,” Kharel said. “Our method gives water agencies and utilities a way to account for that difference, so they can see where more testing would help and be clearer about what they do and do not know.”
The research was supported by seed funding from TCU’s Natural Resource Research Initiative, directed by Harvey, and used computing resources from the STREAM Lab (Sustainable Tools for Risk Evaluation and Climate-Water Modeling) in the Department of Environmental and Geological Sciences, which Kharel leads. The paper, “Censoring-Aware Models Quantify Systematic Underestimation of PFAS Occurrence in U.S. Drinking-Water Monitoring,” is available online.