Passive sampling of per- and polyfluoroalkyl substances (PFAS) in wastewater, sludge and biosolids: Techniques,...

The chemical behaviour and fate of per- and polyfluoroalkyl substances (PFAS) in wastewater treatment are not well understood, particularly regarding the "black-box" nature of the transformation of precursor compounds to smaller and more mobile byproducts in wastewater effluent, sludge and biosolids. The wide range of potential PFAS parent compounds, fluorinated precursors, by-products and degradation products can make monitoring procedures complex and labour-intensive. Inconsistent PFAS inputs and outputs in wastewater treatment processes, both in concentrations and specific compounds, can further complicate monitoring. Passive sampling provides a time-weighted average of PFAS concentrations over days or weeks increasing sampling sensitivity for transformation products and intermediate compounds at low concentrations and is less affected by periodic fluctuations in PFAS levels that may skew grab sampling results. Passive sampling technologies based on solid-phase extraction have been used to monitor a variety of contaminants, including PFAS, in water sources and sediments, and there is interest in adapting these technologies for complex wastewater and sludge matrices. This article summarizes the current state of passive sampling methods applied for PFAS detection in wastewater-related matrices, evaluates key case studies demonstrating their application, and discusses analytical techniques used for PFAS quantification post-sampling. Additionally, the review outlines evolving regulatory frameworks targeting PFAS, highlighting the need for sensitive, reliable, and cost-effective monitoring approaches to support compliance. Overall, passive sampling is a promising tool for PFAS detection and environmental surveillance, and further research into wastewater and sludge matrices is recommended to establish detection limits across different uses.