Researchers from Duke University have solved a longstanding mystery of the origin of high levels of PFAS contamination in water sources in the Piedmont region of North Carolina.
By sampling and analysing sewage in and around Burlington, the researchers traced the PFAS contamination to a local textile manufacturing plant.
The source remained hidden for years because the facility was not releasing regulated, monitored chemical forms of PFAS.
Instead, it was discovered that solid nanoparticle PFAS “precursors” degrade into the chemicals that current tests are designed to detect.
“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 research.
“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.”
Extremely high levels of PFAS found in waterways across North Carolina
PFAS made headlines in North Carolina in 2015, when an EPA study found GenX and other PFAS at high levels in the Cape Fear River.
The discovery set off a domino effect, with study after study finding PFAS contamination in places they shouldn’t be, such as the Wilmington public water supply and hundreds of local wells.
One example of unacceptably high PFAS levels 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, which supplies the town’s 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.
Ferguson explained: “As soon as they shut that process off, the measurable PFAS levels in the wastewater came way down.
“However, 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.”
Burlington’s wastewater treatment was turbocharging PFAS contamination
The researchers discovered that these precursors were being released into the sewer system at concentrations up to 12 million parts per trillion – approximately 3 million times the Environmental Protection Agency’s 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, which are commonly used as fertiliser across the region, the findings indicate PFAS contamination will continue to leach into the region’s soils and waterways for decades to come.
The Clean Water Act: Bringing down PFAS levels for a healthier future
Moreover, a colleague in the department of textile engineering, chemistry, and science at North Carolina State University provided a sample of a water- and stain-repellent 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 wastewater from a specific manufacturer, which had been discharged to the city’s sewage system.
With this information in mind, the town of Burlington worked with a textile manufacturer to change its process and reduce the concentrations of these nanoparticles, using its pretreatment authority under the Clean Water Act.
Ever since, the amount of PFAS precursors coming into Burlington’s wastewater treatment facility has been orders of magnitude lower.
This drop in PFAS contamination levels is a strong indicator that these issues can be addressed at their source rather than through new treatment processes that remove difficult-to-degrade PFAS molecules.
However, the mystery is still not fully understood. “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.
He concluded: “That is an area that still needs more funding and research for us to fully understand.”
