Per- and polyfluoroalkyl substances (PFAS) in final treated solids (Biosolids) from 190 Michigan wastewater treatment plants

Trends in concentration, distribution, and variability of per- and polyfluoroalkyl substances (PFAS) in biosolids are characterized using an extensive dataset of 350 samples from 190 wastewater treatment plants (WWTPs) across Michigan. All samples are comprised of final treated solids generated at the end of the wastewater treatment process. Concentrations of both individual and Σ24 PFAS are log-normally distributed, with Σ24 PFAS concentrations ranging from 1—3200 ng/g and averaging 108 ± 277 ng/g dry wt. PFAS with carboxyl and sulfonic functional groups comprise 29% and 71% of Σ24 PFAS concentrations, respectively, on average. Primary sample variability in concentration is associated with long-chain PFAS with higher tendency for partitioning to biosolids. Short-chain carboxylic compounds, most notably PFHxA, are responsible for secondary concentration variability. Usage of FTSA and PFBS replacements to long-chain sulfonic compounds also contributes to variance in biosolids concentrations. Sulfonamide precursor compounds as a collective group are detected at a similar frequency as PFOS and often have higher concentrations. Trends in PFAS enrichment for individual PFAS vary at least 3 orders-of-magnitude and generally increase with compound hydrophobicity; however, partitioning of PFAS onto solids in WWTPs is a complex process not easily described nor constrained using experimentally-derived partitioning coefficients. Biosolids generated from wastewater treatment generally become enriched in PFAS, an emerging environmentally-persistent contaminant known to cause adverse health impacts to humans and bioaccumulate within ecosystems. Biosolids are then either land applied or landfilled, and in some cases, incinerated, providing pathways for which PFAS can continuously cycle between engineered systems and the environment. This study investigates the composition, distribution, and variability of PFAS in the the largest known biosolids sample population collected in the U.S. to date, representing a geographically-diverse range of WWTPs serving communities of various sizes and industrial activity.