Fate of per- and polyfluoroalkyl substances at a 40-year dedicated municipal biosolids land disposal site

Abstract

The fate of per- and polyfluoroalkyl substances (PFAS) was evaluated at a site where municipal biosolids have been applied annually for 38 years as a waste management strategy. Soil cores (1.8 m in 30-cm sections), groundwater from four wells, and biosolids applied in 2022 were analyzed for PFAS (54 targeted, 17 semi-quantified) using liquid chromatography high resolution mass spectrometry including suspect screening. Total PFAS concentrations decreased with soil depth from 1700 ng/g to 2.06 ng/g. PFAS distribution in 2022 biosolids were 60 mol% perfluoroalkyl acid (PFAA) precursors and intermediates. The surface soil was dominated by long-chain PFAAs (67–76 mol%) reflecting precursor degradation after biosolids application. Presence of semi-quantified intermediates further reflects precursor degradation in surface soil. Long-chain PFAAs diminished with depth while short-chain PFAAs increased with up to 98 and 96 mol% short-chain PFAAs in the bottom depth and groundwater, respectively. PFAS distribution with depth is consistent with chain-length dependent sorption-impacted transport and the high organic carbon content of the surface soil (15.2 % OC) which subsequently decreased with depth (~2–3 % OC at >60 cm). High organic carbon content in the upper horizon is likely from decades of high biosolids application rates, which contributed to minimizing leaching of long-chain PFAS. While the well within the dedicated land disposal is not drinking water, for comparison only, PFAS concentrations in this well only marginally exceeded the EU drinking water directive for total PFAS and a few individual short-chain PFAS, but did exceed tenfold, the USEPA drinking water standard for PFOA.