This proof-of-concept project aims to improve the understanding of the partitioning behavior of per- and polyfluoroalkyl substances (PFAS) with iron (Fe) species in soils. Specifically, it seeks to address the limitations of traditional models by integrating the lognormal Langmuir (LNL) isotherm model. This project will demonstrate that the parameters extracted from these isotherms correlate with soil Fe phases. The ultimate goal is to produce a proof-of-concept model with parameters that can be used to predict sorption based on chemical parameters, such as PFAS molecular weight.

The first step of this project will be a comprehensive literature review to collect data on perfluorooctane sulfonic acid (PFOS) sorption in soils. Then, the LNL model will be fit to derive sorption parameters and its applicability will be evaluated. Subsequently, a selection of soils previously studied in SERDP projects will be characterized using 57Fe Mössbauer spectroscopy to classify Fe species into phyllosilicates, well-crystalline phases (e.g., hematite), and poorly crystalline phases (e.g., ferrihydrite). Based on this analysis, nine representative soils will be chosen for laboratory experiments. Laboratory experiments will evaluate PFOS sorption behavior in the selected soils, with the resulting data fitted to the LNL model. Correlations between LNL-derived sorption parameters and Fe speciation will be established to validate the proof-of-concept predictive approach. Dupplementary experiments will test the sorption of other PFAS, including perfluorooctanoic acid and perfluorohexane sulfonate, on one selected soil. Ultimately, the experiments will examine whether fitted parameters reliably correlate with PFAS molecular weight.

This research will provide a proof-of-concept for an improved model similar to ppLEFRS Abraham for PFAS sorption in soils. By integrating advanced isotherm models and spectroscopic techniques, this project will address critical knowledge gaps, offering a framework for predicting PFAS behavior in soils based on soil characteristics and PFAS molecular weight. The modeling effort is crucial for studying the toxicology of PFAS in sediments and soils, and the outcomes will inform risk assessments, management, and regulatory strategies, ultimately bolstering operational capabilities and warfighter preparedness by mitigating the impacts of these chemicals. (Anticipated Completion Date - 2027)