Per- and poly-fluoroalkyl substances (PFAS): levels, transformation and emissions in Australian wastewater treatment plants

In Australia, per- and polyfluoroalkyl substances (PFAS) are a contaminant of emerging concern. PFAS have unique properties that make them useful for many industrial, commercial and manufacturing processes. However, many PFAS are persistent, and mobile, with some possessing bioaccumulative and/or toxic properties. Due to the past use, and legacy contamination associated with PFAS, the characterisation and reduction of their environmental emissions have become regulatory priorities in Australia; with wastewater treatment plants (WWTPs) as a key focus.  Analytical methods were developed and applied to wastewater treatment plant matrices for 53 PFAS (from 14 compounds classes). PFAS levels in solid and aqueous matrices at nineteen Australian WWTPs were investigated. This investigation revealed an increase of some PFAS (specifically perfluoroalkyl carboxylic acids; PFCAs) during the treatment process and principle component analysis demonstrated strong associations between high PFAS levels and increased trade waste inputs. At a single WWTP, the addition of coagulants appeared to aid the sorption of PFSAs at the dissolved air floatation and filtration plant. Many newly measured PFAS in Australia were present and accounted for up to 53% of the solid and up to 16% of the aqueous Σ45PFAS concentrations. The increase of PFCAs after secondary treatment, and the detection of direct PFCA precursors and their degradation intermediates, presented strong evidence that PFCA precursor transformation was occurring in the secondary treatment sludge. At the marine outfall of a WWTP discharging into Melbourne¿s Port Phillip Bay, PFAS concentrations in aqueous samples were lower pre-outfall compared to post-outfall in the prevailing current direction. At the effluent discharge point, Σ45PFAS in aqueous samples reduced by approximately four-fold over 250 m, and no PFAA precursors were detected in aqueous samples from throughout the bay. An unusually high rainfall event appeared to increase PFAS concentrations in seawater demonstrating that other freshwater inputs to the bay other than the WWTP play an important role in PFAS mass-fluxes in Port Phillip Bay. A similar PFAS signature was present in sediment for three sampled locations within the Melbourne urban/industrial area (this included at the WWTP outfall); indicating a shared source. The PFOS loading in sediment for Port Phillip Bay was calculated at 558 kg, suggesting that partitioning of PFAS to sediment must be considered in future risk assessments.