Civil and Environmental Engineering


Document Type


Date of this Version



Ma H, Li Y, Shen C, Chrysikopoulos CV and Kim H (2021) Editorial: Advances in Pollutant Transport in Critical Zone Environments. Front. Water 3:693102. doi: 10.3389/frwa.2021.693102




One major environmental challenge facing humankind is the constantly increasing pollution of water and soil resources on a global scale. The substances that cause such pollution arise primarily from human-made wastes, including agricultural and industrial wastes, household garbage, oil spills, and other toxic materials. The spatiotemporal distribution of these polluting substances in soil and water systems is determined by an interplay of many factors such as physicochemical properties of pollutants, soil grain properties and structure, fluid flow chemistry and velocity, biological activity, and other environmental factors (temperature, precipitation). In this issue, we have collected a series of articles that advance our fundamental understanding of the transport of solute and colloidal pollutants, their spread in Critical Zone environments, and recent monitoring and control efforts. These articles address the issue from various perspectives, spanning pore-scale, continuum-scale, and field studies in saturated groundwater and vadose zones. Water and soil resources are valuable but finite. Their loss and degradation may not be recoverable within a human lifetime, especially when pollutants do not breakdown and tend to be persistent in the environment. As revealed in a case study from a historical fire training site in New South Wales, Australia (Bekele et al.), despite that the source of contaminants (e.g., aqueous film forming foam for firefighting) was stopped about 20 years ago, the contaminants themselves (i.e., PFAS—perfluoroalkyl and polyfluoroalkyl substances) can remain in and around the site with considerably high concentration, posting as ongoing sources for contamination to groundwater systems for years to come. The fate and transport of PFAS are found to correlate greatly with soil geochemical properties (e.g., soil type, pH) as they migrate in the vadose zone toward the groundwater table. As these synthetic PFAS have been widely used in many industries (including coating, food packaging, cleaning products, fire-fighting foams), the threat these materials pose to the environment and humans cannot be exaggerated.