Vadose zone interfacial dynamics dictating per- and polyfluoroalkyl substances (PFAS) detection, transport, and remediation: a review

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Per- and polyfluoroalkyl substances (PFAS) have emerged as persistent contaminants of significant concern due to widespread use. The vadose zone plays a critical role in PFAS fate and transport, as a temporary reservoir, trapping PFAS, and a conduit to groundwater. This paper reviews the current status and future challenges in detecting, predicting fate, and remediating PFAS in the vadose zone. The paper first evaluates detection technologies, highlighting sensitivity and reliability across environmental matrices and remaining challenges (i.e., emerging PFAS, the lack of real-time in-situ monitoring). PFAS fate and transport are then examined within the vadose zone, where interfacial processes and environmental conditions significantly affect PFAS mobility. Critical gaps in transport modeling are identified, emphasizing the need for long-term field data and system-specific studies. Furthermore, current and emerging technologies (e.g., novel materials) for remediation are assessed for their potential to enhance PFAS removal. Treatment effectiveness varies based on PFAS chain length, environmental conditions, treatment duration, and scalability. Challenges in translating laboratory success to field applications, maintaining long-term performance, managing treatment residuals, and meeting regulatory targets are also discussed. The novelty of this review is grounded in deciphering PFAS interfacial dynamics in the vadose zone and the potential of machine learning and deep learning to overcome knowledge gaps and challenges caused by the complex interfacial interactions. Bridging pore-scale retention and field-scale predictability can help optimize detection, transport modeling, and remediation. This framework redefines the unsaturated subsurface as a contaminant reservoir, providing a predictive roadmap for managing this persistent groundwater contamination source.