Environmental sustainability has attracted the most attention among the three sustainability indicators (Figure ). In the majority of studies, TRACI and ReCiPe methodologies have been commonly employed to evaluate the environmental sustainability of GAC and IX technologies across various water types. However, environmental footprint was utilized to assess the environmental impact of GAC in fire extinguishing water, while Impact 2002+ was employed for subcritical water decomposition technology in subcritical water. Variations within GAC or IX technologies, such as single-use GAC adsorbents, singleuse IX resins as well as methods for reactivation and regeneration, each carry distinct environmental implications and tradeoffs. The multitude of options available for selection between these technologies significantly influences the results of LCAs. However, numerous studies suggest that from an environmental sustainability standpoint, IX generally exhibits lower environmental impacts compared to GAC. IX systems have lower media usage rates (mass of adsorbent media required to treat a given volume of water) due to higher adsorption capacity and longer bed life, leading to less frequent media replacement, and fewer environmental impacts from production and disposal. For instance, single-use IX resins have lower environmental impacts in all indicators except ozone depletion compared to regenerable resins and GAC adsorbents. Further research supported these findings, showing lower overall environmental impacts for IX when removing long-chained PFAS from groundwater. Another study found that GAC generates higher average impacts, excluding ozone depletion, compared to IX-based technologies at various PFAS concentrations. The high ozone depletion impacts from single-use IX resins are due to the release of ozone-depleting chemicals during their production. Despite these impacts, GAC has shown potential in specific treatment scenarios.