Per‐ and Polyfluoroalkyl Substances (PFAS) in Subsurface Environments: Occurrence, Fate, Transport, and Research Prospect.

Per‐ and polyfluoroalkyl substances (PFASs), also known as "forever chemicals," are manmade chemicals that have been increasingly detected in various geological settings since the early 2000s. The soil and subsurface environments are the geological media commonly affected by PFAS. We conducted a comprehensive review of peer‐reviewed articles published from 2010 through 2022 concerning the fate and transport of PFAS in subsurface environments. This review is organized into different subsections, covering the basics of PFAS properties and how they affect the occurrence, fate, and transport of PFAS, the fundamental processes affecting subsurface transport and fate of PFAS, and mathematical models for describing and predicting PFAS transport behaviors. Mechanisms governing PFAS transport in the subsurface environment, including the sorption of PFAS at the air‐water interface, solid‐water interface, and nonaqueous phase liquids‐water interface, were explored in detail. Challenges and future research priorities are identified to better mitigate the global challenges of PFAS contamination. Plain Language Summary: Per‐ and polyfluoroalkyl substances (PFASs) are a group of manmade chemicals used in a multitude of applications and commercial products (clothing, cookware, cosmetics, personal care products, fire extinguishers, etc.). Their widespread use has, however, lead to increasing release and distribution in terrestrial and aquatic ecosystems. PFAS, due to their unique properties, are very persistent in the environment as they do not degrade easily. Unfortunately, they are also toxic to organisms, including humans. In this review, we discuss the omnipresence of PFAS in water and soil and explain how PFAS move through subsurface media. There are thousands of different PFAS compounds, and only few of them have been studied in more detail and their transport behavior is known. PFAS tend to accumulate at the air‐water interface in the vadose zone. Generally, PFAS with long carbon chains are retained in soils more strongly than short‐chain compounds. Negatively charged PFAS are more mobile in soils than neutral and positively charged PFAS, and thus can readily pollute groundwater. Nonetheless, due to their persistence and slow desorption, even more strongly sorbed PFAS can be a sustained source for groundwater pollution. We finally identify challenges and future research needs to address the emerging threat of PFAS contamination of the environment. [ABSTRACT FROM AUTHOR]