Partitioning, mobility and persistence of PFAS in biosolids-based compost products across solid and aqueous matrices

Persistence, release, and mobility of per- and polyfluoroalkyl substances (PFAS) from composted biosolids with vegetative waste were evaluated across multiple environmental matrices. Laboratory experiments were conducted to characterize PFAS release into water at pH 7.5 to simulate post-application conditions. Samples of biosolids-based fresh compost, two types of compost for turf use and agricultural uses, screen overs (larger particles separated from fresh compost), and fresh vegetative waste, as well as leachates collected after 24-hour mixing of these samples with deionized water, were analyzed for 40 PFAS following a modified U.S. EPA Method 1633 procedure. Partitioning of PFAS in the solid samples and in the leachate produced after 24 h was evaluated for the 15 predominant PFAS detected at the highest concentrations. Results showed strong matrix-dependent behavior, with long-chain PFAS exhibiting greater retention in solid matrices and short-chain PFAS preferentially mobilizing to the aqueous phase. Sulfonates showed higher affinity for the vegetative fraction than carboxylates. Screen overs were enriched in precursor compounds, suggesting preferential partitioning of precursors to the vegetative fraction during compost curing and screening. These findings indicate that composting alters PFAS partitioning by modifying organic matter composition, resulting in rapid release of short-chain PFAS and slower release of long-chain PFAS and precursors as the solid organic fraction decomposes. This dual-release behavior has important implications for groundwater transport and PFAS mobilization following land application of compost, and for assessing the environmental risks of biosolids-based composts.