Occurrence of per- and polyfluoroalkyl substances (PFAS) and their precursors in biosolids across 15 U.S. states
The US Environmental Protection Agency (EPA) draft sewage sludge risk assessment indicates that land application of biosolids containing as little as 1 ng/g of perfluorooctanoate (PFOA) or perfluorooctane sulfonate (PFOS) may exceed human health risk thresholds. This study provides updated measurements of per- and polyfluoroalkyl substances (PFAS) in US biosolids. Twenty-seven biosolid samples from 15 states were analyzed using EPA Method 1633 and the total oxidizable precursor (TOP) assay. Dominant PFAS included 5:3 fluorotelomer carboxylic acid (FTCA) (70.2 ± 84.7 ng/g), 7:3 FTCA (23.7 ± 43.7 ng/g), and PFOS (22.1 ± 45.2 ng/g), with total PFAS ranging from 2 to 807 ng/g, showing no correlation with sewer-shed population or industrial inputs. At one facility, PFAS increased from 17.3 ng/g in primary sludge to 150 ng/g in centrifuge cake, consistent with precursor transformation. TOP assay did not increase total PFAS levels but shifted the profile, with perfluoroalkyl carboxylic acids increasing and FTCAs and other precursors decreasing, likely reflecting incomplete transformation of precursors during wastewater and sludge treatment. These findings suggest that regulated PFAS will increase following land application due to transformation of precursors over time. Compared to the 2001 national sewage sludge survey samples, PFOA and PFOS declined by > 80%, yet remain at least one order of magnitude above 1 ng/g. Current study supports EPA’s conclusion that land application of biosolids continues to pose potential human health risks.