State study finds PFOS widespread in biosolids; DEQ advancing monitoring and minimization rules

The North Carolina Division of Water Resources presented results from a 2023 sampling study of wastewater, biosolids and soils that found PFAS widely detectable across sampled facilities and fields. Dr. Angela Moore, who led the analysis, told the Science Advisory Board that the study used a modified EPA 537.1 method covering 57 PFAS analytes and that results were normalized to dry weight for biosolids and soils.

Moore highlighted three headline findings: PFOS was detected in the majority of biosolids samples (about 83% of tested facilities), wastewater influent and effluent frequently had quantified PFOA or PFOS above the 4 ng/L comparison metric, and PFOS was found in every composite soil sample from land-application fields included in the study. "PFOS was found in all of the composite soil samples that we collected," she said.

Study scope and methods: The study sampled 37 wastewater treatment plants (including domestic, industrial and municipal plants), collected influent, effluent and biosolids samples and analyzed soils from 19 land-application fields (0–6 inch composites). Moore said effluent concentrations were generally lower than influent but that transformation of precursors can increase measurable compounds in effluent. She said detection limits varied by matrix and sample (some influent detection limits reached 200 ppt, though most were near or below 20 ng/L).

Comparative context and mass balance: Moore compared North Carolina results to other states and federal draft risk assessments and concluded North Carolina's maximum observed biosolids PFOS concentrations (up to about 92.6 ng/g dry-weight in this dataset) fall within the range reported elsewhere. Her mass-analysis estimate indicated that the majority — roughly 87%–98% — of the quantified PFAS mass measured in the study exits wastewater plants in effluent, while about 2%–3% is associated with biosolids.

Limitations and next steps: Moore emphasized the study was a broad informational survey, not a regulatory action. She noted the team did not collect background soil samples, which limits the ability to attribute low-level soil detections to biosolids application versus other sources. The final technical report is in preparation and DEQ said proposed monitoring and minimization rules have been advanced for public comment; the division also plans targeted groundwater sampling at some dedicated land-application sites that already have monitoring wells.

Public-health and regulatory implications: Board members asked about load (concentration times flow) as a metric to compare facility types; Moore agreed it is an important context point for future public presentations. DEQ emphasized collaboration with utilities, academic researchers and affected stakeholders as it moves toward rulemaking and more targeted monitoring.

The board did not vote on regulatory measures at the meeting; DEQ said it will post the technical report and the study data to its project website and accept public comments on proposed rules during the comment period.