Distribution coefficients of PFAS in activated carbon: Literature evaluation and comparison of sorption data

Evaluating per- and polyfluoroalkyl substances (PFAS) sorption to activated carbons (AC), particularly through solid–liquid distribution coefficients (Kd), is important for selecting suitable water purification materials for in situ and on-site remediation. However, Kd values are not always reported in sorption studies, and when they are, tend to be scattered and difficult to compare. Here we compiled batch sorption data for 18 PFAS (i.e., 255 entries), including anionic ultra-short, short- and long-chain compounds, on granular, powdered, and colloidal AC, together with metadata on AC properties and solution chemistry. Reported sorption isotherms are, for the first time, collectively visualized and compared with previous sorption predictions via Polanyi Adsorption Potential Theory. These show generally an overall agreement, consistent with pore filling as an important sorption mechanism and validating previous estimations. Nonetheless, significant scatter across AC materials was noted for many PFAS, likely due to the different AC properties, water chemistries and experimental setups. To quantify this variability, cumulative distribution functions are fitted to log Kd populations for each PFAS as means to derive percentile ranges. The log Kd values resulting from the 50th percentiles increased with PFAS molecular weight, and scaling trends for AC were comparable to soils, although the magnitude in Kd in soils was orders of magnitude smaller. Moreover, for AC, these trends were similar to those found for other hydrophobic organic contaminants when Kd values were related to molar volumes. Overall, the dataset and median Kd values provide a screening-level resource for practitioners evaluating AC-based treatment of contaminated water.