Distribution and mass load of per- and poly-fluoroalkyl substances (PFAS) in the sediments of a shallow urbanised marine embayment in south-eastern Australia.

This study examined the spatial distribution, partitioning, and mass inventory of per- and polyfluoroalkyl substances (PFAS) in the waters and sediments of a shallow marine embayment. The aim was to understand where catchment derived PFAS are ultimately distributed. Six 60 cm sediment cores from various depositional environments were analysed for 44 PFAS, with 11 compounds detected. The Σ44 PFAS burden was estimated at 14.1 tonnes, located mostly at depths of 6-18 cm. The sediment Σ44 PFAS composition was estimated to be mostly 6:2 fluorotelomer sulfonic acid (2.7 kg/km2) and perfluorohexane sulfonate (2.9 kg/km2). The remainder was composed of perfluorooctanoic acid, perfluorobutanoic acid, perfluorobutane sulfonate, perfluorohexanoic acid, perfluorooctane sulfonate, and 4:2 fluorotelomer sulfonic acid, at concentrations of 0.02-0.7 kg/km2. The central basin (1032 km2) was the primary PFAS sink, containing an estimated Σ44 PFAS mass of 7.0 tonnes, approximately 50% of the total PFAS burden. In contrast, surface sediment grab samples indicated an estimated Σ44 PFAS total sediment load of only ∼23 kg (0.2% of the core estimate). Surface water samples indicated an estimated Σ44 PFAS mass in the water column of ∼199 kg (∼1.4% of the sediment). Sediment/water partition coefficients ranged from 0.9 to 118.7 L/kg. The results expand our knowledge of PFAS environmental fate and transport. They demonstrate that i) sediments in shallow embayments can act as large PFAS sinks; ii) PFAS deposition is variable and depends on sediment physicochemical properties, transport, and depositional settings; and iii) grab samples may miss PFAS >6 cm below the sediment surface.