Fate, behaviour and ecological impact of biosolids derived per and polyfluoroalkyl substances (PFAS)
Creators: name: Moodie, Damien
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 410599
subject: Pollution and contamination not elsewhere classified

description: This study was initiated to assess the potential impacts of wastewater treatment plant biosolids derived per and poly-fluoroalkyl (PFAS) on the Australian environment. The objectives of the study were to review the literature to better understand the current state of knowledge regarding PFAS contamination of sewage sludge and biosolids, and to understand where and how Australia fitted into the global regulatory story. Fieldwork was undertaken to identify what were the main PFAS of concern in Australian biosolids and whether the contamination trends witnessed in the Northern Hemisphere repeated in aged Australian sewage sludge/biosolids. An assessment of background PFAS contamination of western Victorian soils was also undertaken.

The comprehensive literature of global PFAS levels in wastewater treatment plant sludge/biosolids (Chapter 2) revealed that the eight-carbon chain perfluorooctanesulfonic acid (PFOS) was the most detected compound in the greatest abundance followed by perfluorooctanoic acid (PFOA). The review highlighted the lack of knowledge regarding precursor compounds in Australian sewage sludge/biosolids; and the influence that transformation of precursor PFAS has on loads going through WWTPs and their possible sources.

A review of international PFAS in biosolids regulations (Chapter 3) revealed a lack of definitive PFAS in biosolids regulations. In that context, only Maine, USA, had, at the time of writing, set upper limits of PFAS for “beneficial use of solid wastes,” although Denmark, Germany, The Netherlands, Sweden and Australia had set PFAS limits in soils. No other countries were found to have PFAS limits relating to biosolids or their use; this was in some part reflective of the lack of industrialization and centralized wastewater management in many parts of the world.

To gain a better understanding of PFAS contamination of Australian biosolids, a thorough investigation of biosolids collected from 19 wastewater treatment plants (WWTPs) was undertaken during 2018 (Chapter 4). The 19 WWTPs cover a range of catchment types and treatment technologies. Samples were analyzed for 44 PFAS using isotope dilution and alkaline extraction coupled with quantification with LC-MS/MS. The ∑44PFAS mean concentration was 260 ng/g dry weight (dw) with individual concentrations ranging between 4.2 and 910 ng/g dw. The dominant compound class detected were the di-substituted phosphate esters which contributed 45% of the total mean ∑44PFAS mass, followed by perfluoroalkyl carboxylic acids (∑11PFCAs) contributing 17% of the mass, and the perfluoroalkyl sulfonates (∑8PFSAs) which contributed 16%. Using population data supplied by the participating WWTPs, the mean annual estimated biosolids-associated PFAS contribution is 6 mg per person per year, ranging between 0.6 mg and 15 mg. A similar population 1 normalized concentration regardless of WWTP, region or capacity suggests that the domestic environment provides the baseline PFAS loading. Statistically significant higher ∑44PFAS and PFOS concentrations were observed at urban locations. A weak correlation was observed between annual mass of PFAS associated with each individual WWTP and their percentage industrial waste contribution. This may be important for elevated PFAS concentrations observed in WWTPs with higher industrial waste inputs; and requires further research. 

To gain a better understanding of PFAs concentrations in Australian stabilized sewage sludge, and particularly if there had been any significant change to PFAS concentrations over time, and especially post PFAS regulation, samples of stabilized sewage sludge produced by two WWTPs from 1970 to 2017 were evaluated (Chapter 5). The stabilized sewage sludge had been stored outdoors in windrows for pathogen reduction and to improve the stabilized sewage sludge quality. PFAS were detected in all stabilized sludge stockpile samples, with the mean Σ48PFAS being 1322 ng/g, ranging between 74 and 8842 ng/g. The highest contributors to the Σ48PFAS mass were from the Σ1diSAmPAP followed by the Σ8 FOSA/E/AAs, Σ9PFSAs and the Σ11PFCAs. The most abundant (frequency, mass) PFAS was diSAmPAP, while the most abundant PFSA detected was PFOS and the most abundant PFCA was PFOA. PFCA and PFSA precursors and intermediate compounds including diSAmPAP, diPAPs, FTSAs, FTCAs, and FOSA/E/AAs were also detected as part of this study. PFOS was ubiquitously present in Australian stabilized sewage sludge samples and showed an increasing concentration trend in stockpiled sludge dating from 2004 up to 2018.

The end use of beneficial biosolids application is often as a land applied agricultural fertilizer supplement. While Australia has no history of direct PFAS manufacturing, per and polyfluorinated compounds have a long history of widespread usage including in firefighting foams, industrial applications, and end use consumer products. To determine the baseline level of 44 PFAS in rural and urban soils in the state of Victoria (Australia) a survey of surface soils was conducted at 50 separate sampling sites covering population distributions ranging from 1 to 444 people per square kilometer (Chapter 6). PFAS were detected in 100% of the samples screened in this study. PFOS was quantified above the method detection limit at 82% of surveyed sites and was at a concentration &gt;0.5 ng/g at all urban soil survey sites, regardless of population density (max 4.8 ng/g), while the 4- carbon chain perfluoroalkyl acid PFBA (range &lt;0.6 – 6 ng/g) was quantified at 80% of surveyed sites making it the most abundant PFCA quantified as a part of this survey. This study provides the first assessment of background PFAS concentrations in Australian soils.

Together, the information gathered as a part of this investigation helps to gain a better understanding of the PFAS concentrations contained in Australian biosolids and to what extent the 2 main influencing compound classes, including perfluoroalkyl sulfonates and carboxylic acids and precursor compounds, especially the PAPs, have on Australian PFAS in sludge/biosolids loads. Together with the historical information from analysis of aged, stabilized sewage sludge stockpiles, a concerning lack of overall decreasing trends of PFAS discharges to Australian WWTPs, as well as the limited influence of regulations on PFOS mass discharges to WWTPs, has been shown. The WWTP PFAS concentration data combined with baseline PFAS in soil data from regional Victoria that showed a ubiquitous PFAS presence at trace levels, provides a fuller picture of the possible impacts PFAS impacted biosolids may pose, and the feasibility of long term PFAS compromised sludge/biosolids land applications is discussed.