Uncovering the source of widespread ‘forever chemical’ contamination in North Carolina

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 regulated and 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.

Published November 18 online in the journal Environmental Science & Technology Letters, the findings provide both a warning and playbook for others worried about the worldwide spread of these forever chemicals.

“We have some of the most sophisticated instruments in the world for PFAS analysis, and we couldn’t detect these until we dramatically changed our approach,” said Lee Ferguson, professor of civil and environmental engineering at Duke, who led the years-long effort. “Sometimes we don’t know what we don’t know, and there is a lesson to be learned about blind spots in our analyses when it comes to looking for new PFAS in the environment.”

In the early 2010s, it was discovered that per-and polyfluoroalkyl substances, or PFAS, are both harmful to human health and nearly impossible to degrade in the environment. With many different formulations, this class of chemicals have long been used in nonstick frying pans, water–repellent sports gear, stain–resistant textiles, cosmetics, firefighting foam and countless other consumer products since the 1940s.

These forever chemicals made headlines in North Carolina in 2015 when a study from the EPA found GenX and other forms of PFAS at high levels in the Cape Fear River. The discovery set off a domino effect, with study after study finding PFAS compounds in places they shouldn’t be, such as the Wilmington public water supply and hundreds of local wells.

Funded by an initial $5 million grant from the NC General Assembly in 2018, the state of North Carolina created an ambitious statewide testing network to monitor PFAS levels in the state’s drinking water. Led by Ferguson and colleagues from North Carolina State University and the University of North Carolina at Chapel Hill, the network represents a wide–ranging attempt to monitor the compounds’ presence in drinking water supplies in 405 municipalities across the state.

“There’s never been a large-scale chemical pollutant source and distribution study done like this before anywhere in the country,” said Ferguson.

One such locale of unacceptably high levels of PFAS was the town of Pittsboro, NC. Early results from the statewide testing network indicated that the contamination was likely coming from upstream in the Haw River, from which the town gets its drinking water. This led researchers to Burlington’s wastewater treatment plant, which releases its treated water into the river upstream of Pittsboro.

Confusingly, tests showed much higher levels of PFAS coming out of the facility than going into it. This indicated that PFAS precursors that do not show up on routine tests were entering the plant and being transformed during treatment. Burlington was at the time using a treatment method produced by Zimpro that uses heat and pressure to break down complex organic compounds. The process, unfortunately, was also converting these PFAS precursors into more dangerous forms of these forever chemicals.

“As soon as they shut that process off, the measurable PFAS levels in the wastewater came way down,” said Ferguson. “But the precursors were still coming into the facility and being concentrated into sludge that is eventually spread on agricultural fields, where they will transform to regulated forms of PFAS over time. We needed to find the source.”

Led by Patrick Faught, a PhD student in Ferguson’s lab, the researchers began the hunt. Faught worked with the City of Burlington to obtain samples of wastewater and raw sewage from dozens of places upstream of the wastewater treatment plant. But the samples’ levels of known PFAS precursors were far too low to explain the measurements taken at the treatment facility. Undaunted, Ferguson suggested putting the samples through a process that mimics the facility’s former treatment technology.

“After turning all the available PFAS precursors into measurable forms of PFAS, the levels in one textile manufacturer’s wastewater jumped 50,000 to 80,000 percent,” Faught said. “I jumped out of my chair when I saw the results.”

“It’s the most dramatic result I’ve ever seen in my lab,” Ferguson added. “It contaminated all of our instruments for over a week.”

Faught and Marzieh Shojaei, a postdoctoral researcher in the Ferguson lab, spent the next six months trying to pin down which precise PFAS precursors were in the samples. But time and again, they came up empty. Eventually, the team thought to look for particulate forms of PFAS precursors suspended in the textile wastewater rather than dissolved chemicals. After a complex process of filters and centrifuges, they discovered insoluble nanoparticles made of side-chain fluorinated polymers that nobody had reported in an environmental sample before.

What’s more, a colleague in the department of textile engineering, chemistry and science at North Carolina State University provided a sample of a water and stain repellant fabric treatment similar to those used by textile manufacturers discharging to the Burlington sewer. The results from that sample matched almost perfectly with what the team had just discovered in a specific manufacturer’s wastewater discharged to the city’s sewage.

With this information in hand, the town of Burlington worked with that textile manufacturer to change their process and bring down the concentrations of these nanoparticles using its pretreatment authority outlined in the Clean Water Act. Ever since, the amount of PFAS precursors coming into Burlington’s wastewater treatment facility has been orders of magnitudes lower.

“Every system downstream of that facility is also now seeing a significant drop in the amount of PFAS in their drinking water,” Ferguson said.

This drop in PFAS, Ferguson said, is a great indicator that these issues can be taken care of at their source rather than through new treatment processes that get rid of the difficult-to-destroy PFAS molecules. But he also cautions that this story is not yet completely told.

These PFAS precursor nanoparticles have been accumulating in treatment-plant-derived biosolids used as fertilizer across eastern North Carolina for years. This explains another longstanding mystery of why the town of Chapel Hill’s raw drinking water has had elevated levels of PFAS: The PFAS precursor nanoparticles in this biosolids fertilizer essentially act as a slow-release source of PFAS and will continue to do so for many decades to come.

It's an issue that the researchers say many other communities across the country will now have to consider.

“We don’t really understand how long it takes these PFAS precursor nanoparticles to transform in wastewater and biosolids and seep into the surrounding environment,” Ferguson said. “That is an area that still needs more funding and research for us to fully understand.”

This work was performed in collaboration with the Southern Environmental Law Center and the Haw River Assembly. It was conducted through the North Carolina PFAS Testing Network, supported by an award from the North Carolina Collaboratory with funding appropriated by the North Carolina General Assembly.

“Colloidal Side-Chain Fluorinated Polymer Nanoparticles Are a Significant Source of Polyfluoroalkyl Substance Contamination in Textile Wastewater.” Patrick W. Faught, Marzieh Shojaei, Abigail S. Joyce, and P. Lee Ferguson. Environmental Science & Technology Letters, 2025. DOI: 10.1021/acs.estlett.5c01014