An environmental chemistry laboratory at Duke University has solved a longstanding mystery of the origin of high levels of PFAS—so-called “forever chemicals”—contaminating water sources in the Piedmont region of North Carolina.

By sampling and analyzing sewage in and around Burlington, NC, the researchers traced the chemicals to a local textile manufacturing plant. The source remained hidden for years because the facility was not releasing chemical forms of PFAS that are routinely monitored. The culprit was instead solid nanoparticle PFAS “precursors” that degrade into the chemicals that current tests are designed to detect.

Incredibly, these precursors were being released into the sewer system at concentrations up to 12 million parts-per-trillion—approximately 3 million times greater than the Environmental Protection Agency’s recently-enacted drinking water regulatory limit for certain types of PFAS.

While precursors typically degrade slowly over time into types of regulated PFAS, Burlington’s atypical wastewater treatment practices were turbocharging the transformation. With these chemicals especially concentrated in sewage sludge and the resulting biosolids commonly used as fertilizer across the region, the findings indicate PFAS will continue leaching into the region’s soils and waterways for decades to come.