Organic carbon and salinity affect desorption of PFAS from estuarine sediments

Purpose To improve the understanding of the fate and behaviour of per- and polyfluoroalkyl substances (PFAS) in estuarine environments, this study investigated the effect of organic carbon (OC) and salinity on the desorption of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonic acid (PFHxS) from five freshly contaminated estuarine sediments. Materials and methods Batch desorption experiments were completed following sorption experiments in uncontaminated sediments that covered a range of OC contents (1.1-10%), as well as in field-contaminated sediments. PFAS-free seawater of different salinities was used for the desorption. Results and discussion The range of PFAS desorbed from the sediments were consistent with the sorption behaviour of these compounds with the desorption of PFOS notably lower than PFOA and PFHxS. Approximately 9-69% PFOS, 33-91% PFOA and 43-116% PFHxS were desorbed after the 1st 24-h desorption indicating the PFOS' stronger interaction/sorption with the sediments. The lowest percentages of PFAS were desorbed from sediments with high OC content exposed to highly saline conditions. The influence of salinity on desorption was, however, less than OC content which appeared to have a "protective" effect, inhibiting desorption of PFAS from these sediments. These results agree with experiments on field-contaminated sediments. Conclusion Over-all, results point to the importance of both OC and salinity in reducing release of PFAS from contaminated estuarine sediments, with OC being key to controlling PFAS mobility.