Beyond compost solids: system-wide per- and polyfluoroalkyl substances (PFAS) distribution and oxidisable precursor...

Composting of food organics and garden organics (FOGO) supports circular-economy objectives and production of recycled organic products but may facilitate per- and polyfluoroalkyl substances (PFAS) occurrence across multiple matrices within processing systems. While PFAS in finished compost have been reported, information on the system-wide distribution of PFAS, including oxidisable precursors, within full-scale composting facilities remains limited. This study aimed to investigate the occurrence, distribution, and oxidisable precursor potential of PFAS within a full-scale in-vessel FOGO composting facility in Victoria, Australia, focusing on leachate and leachate pit sediments as potential PFAS reservoirs. Targeted analysis of 33 PFAS and the total oxidisable precursor (TOP) assay were applied to feedstock, finished compost, leachate water, and leachate pit sediments. Mean Σ33 PFAS concentrations in feedstock (4.1 μg kg^-1 dw) and finished compost (4.0 μg kg^-1 dw) were comparable. However, PFAS were also detected in leachate-associated matrices with Σ33 PFAS concentrations of 2.7 μg kg^-1 dw in leachate pit sediments and 0.42 μg L^-1 in leachate, highlighting leachate pit sediments as an important PFAS-containing compartment within the leachate collection system. Summed perfluoroalkyl carboxylic acids (ΣPFCAs) increased from 1.7 to 8.0 μg kg^-1 dw in feedstock and from 3.2 to 9.3 μg kg^-1 dw in finished compost following oxidation, demonstrating the presence of oxidisable PFAS precursor potential in both matrices. Leachate pit sediments also exhibited oxidisable PFAS precursor potential. This study provides field-based evidence of PFAS occurrence and oxidisable precursor potential in leachate pit sediments within a full-scale commercial FOGO composting facility. These findings highlight the importance of considering leachate-associated residues alongside finished compost in PFAS assessment and management as regulation of recycled organics evolves.