CHARACTERIZING PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS) IN FINAL TREATED SOLIDS (BIOSOLIDS) FROM MICHIGAN WASTEWATER TREATMENT PLANTS

Per- and polyfluoroalkyl substances (PFAS) are a class of highly persistent environmental contaminants with known toxicity in parts-per-trillion concentrations. Land application of final treated solids (biosolids as defined by the US EPA) generated at wastewater treatment plants (WWTPs) with PFAS may lead to contamination of soil and water resources. The Michigan Department of Environment, Great Lakes, and Energy (EGLE) is proactively evaluating and monitoring PFAS in final treated solids that may be considered for land application across the state, and generated three datasets: 2018 and 2021 Statewide WWTP and Biosolids studies and an ongoing Land Application of Biosolids Containing PFAS Interim Strategy. This work characterizes the concentrations, compositions, and variability of PFAS in 350 final treated solid samples from 197 WWTPs across Michigan compiled from all three datasets and validated to original laboratory reports. Application of quality control/quality assurance measures led to the removal of samples on the basis of inconsistencies in sludge classification, analytical method, and data generated by a subset of analytical laboratories. Of the PFAS detected in the samples, compounds with carboxyl and sulfonic functional groups comprise 29 and 71%, respectively, on average of Σ₂₄ PFAS concentration. Primary sample variability is associated with long-chain PFAS with higher tendency for sorption to solids. Short-chain carboxylic compounds, most notably PFHxA, are responsible for secondary variability and are detected in 77% of the samples. Sulfonamide compounds, namely NMeFOSAA, more significantly contribute to total PFAS than PFOS, with roughly 37% and 24% contributions at the 50^th percentile, respectively. Although toxicological implications of sulfonamide compounds are poorly understood, they are recognized precursors to terminal perfluoroalkyl acids (e.g., PFOS). Further consideration of sulfonamide compounds, their concentrations and transformation rates, may be necessary for developing screening criteria for land applied biosolids. Coupling the PFAS characterization herein with a contaminant transport model may provide valuable predictions of PFAS fate and transport at land application sites.