Oral Presentation Society of Environmental Toxicology and Chemistry Australasia 2021

Sorption of per- and polyfluoroalkyl substances (PFAS) in Australian soils (#74)

Divina Navarro 1 , Shervin Kabiri 2 , Rai Kookana 1 , Mike McLaughlin 2
  1. CSIRO, Urrbrae, SA, Australia
  2. School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA, Australia

Sorption is an important concept used in understanding the fate and behaviour of contaminants in the environment. For per- and polyfluoroalkyl substances (PFAS) that have already found its way in soil and aquatic environments, understanding sorption is becoming quite crucial for risk assessment and mitigation/remediation-related decision making. This presentation will provide an overview of different studies on sorption of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonic acid (PFHxS) – three of the most widely detected PFAS – in Australian soils. All the studies were geared toward understanding the role of soil properties on sorption of PFAS and identifying mechanisms driving sorption. Results from the review of scientific literature on sorption, i.e., soil-water partitioning coefficients (Kd), revealed that the traditional Koc-approach is inadequate, and multiple soil properties (not just organic carbon, OC) influence sorption. Sorption of PFAS was then envisioned to occur via hydrophobic interaction with organic matter, ligand bridging through divalent cations, electrostatic interaction with positively charged sites, and surface complexation with oxides. The results from the review were further supported by studies using a large number of Australian temperate soils (n=170) that covered a wide range of soil properties. The study highlighted the importance of pH, silt+clay, and OC on sorption of PFOS, PFOA and PFHxS. In conjunction with Mid-Infrared (MIR) spectroscopy, models relating Kd to MIR soil spectra were developed as a possible way of estimating/predicting Kd of PFAS. Follow up study, which investigated sorption of PFAS in Australian tropical soils, pointed to some differences in the sorption of PFAS in variable-charged soils compared to temperate soils. Over-all, the studies presented will provide an excellent overview of our current understanding of sorption of PFAS in the Australian environment.