Occurrence and transport of per- and polyfluoroalkyl substances (PFAS) within a coastal groundwater aquifer

Understanding the sources, fate, and transport of per- and polyfluoroalkyl substances (PFAS) in coastal aquifers is essential for assessing the risk to these systems. We investigated PFAS concentrations within the Quaternary Aquifer of the Mornington Peninsula, Australia. The goals were to identify the sources of any observed contamination and assess the risk to ecological receptors associated with surface water bodies that interact with the aquifer. Fifteen bores were sampled at various depths. Multiple PFAS were detected in eight bores at ng/L concentrations (maximum ∑₈PFAS = 78.8 ng/L), while seven bores contained no detectable PFAS. Notable compounds included legacy perfluoroalkyl acids, such as PFOA, PFOS, and PFHxS, as well as the fluorotelomers 6:2 FTS and 6:2 diPAP. Several potential sources were identified, including two local landfills, a wastewater treatment plant, and the use of recycled water for irrigation in local agriculture. The bores with the highest total PFAS concentrations were located near the identified sources, particularly the landfills. No clear source was apparent for several PFOS-contaminated bores. Concentrations of PFOS at six bores were just above the current ecological guideline values for 99% species protection (0.00023 μg/L) but below the value for 95% species protection (0.13 μg/L). The risk to aquatic ecological receptors from contaminant discharge from groundwater into local watercourses is considered low, due to relatively low PFAS concentrations and moderate groundwater velocities; however, the combined total risk from seasonal fluxes and surface water runoff, and other discharges could be higher. Further monitoring and risk assessment are therefore recommended.