Oxalate Enhances Desorption of Perfluorooctane Sulfonate from Soils and Sediments

Perfluorooctane sulfonate (PFOS) is one of the most widespread toxic substances in water distribution systems, posing a significant risk to public health and the environment due to its toxic and non-biodegradable nature. In this study, the effect of oxalate on PFOS adsorption/desorption to/from soil and sediment samples was studied with batch experiments. Dissolved organic carbon content in soil strongly enhanced the retention of organic halogens. Oxalate increased PFOS desorption by 1.43- to 17.14-fold and significantly increased the release of dissolved organic carbon and inorganic ions in soils. The effects of root exudates were similar to those of oxalate. Addition of low molecular weight dissolved organic carbon caused partial dissolution of the soil structure (e.g., through formation of organo-mineral complexes), resulting in the release of organic carbon and metal ions and subsequently enhancing PFOS desorption. The effects of oxalate on organic halogen desorption were influenced by dissolved organic carbon content and formation of calcium oxalate.