Per- and Polyfluoroalkyl Substances (PFAS) in Treated Sewage Sludge from Michigan Wastewater Treatment Plants
Abstract
Concentrations, compositions, and variability of Per- and Polyfluoroalkyl Substances (PFAS) in sewage sludge are characterized using an extensive dataset of 350 samples from 190 wastewater treatment plants (WWTPs) across Michigan. All samples are comprised of final treated sewage sludge generated at the end of the wastewater treatment process. Concentrations of Σ24 PFAS are log normally distributed with a range of 1 to 3200 ng/g dry wt. and of average 108 ± 277 ng/g dry wt. Compounds with carboxyl and sulfonic functional groups comprised 29% and 71% of Σ24 PFAS concentrations, respectively, on average. Primary sample variability is associated with long-chain PFAS with higher tendency for partitioning to sewage sludge. Short-chain carboxylic compounds, most notably PFHxA, are responsible for secondary variability and are highly detected in 77% of the samples with average concentrations of 10 ± 30 ng/g dry wt. Sulfonamide precursor compounds, namely N-MeFOSAA, generally contribute more mass to total PFAS than PFOS on average, a well monitored and regulated compound. Trends in PFAS enrichment were found to generally increase with compound hydrophobicity; however, the partitioning of PFAS onto sewage sludge in WWTPs is a complex process not easily described nor constrained using experimentally derived partitioning coefficients.