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Communication Dans Un Congrès Année : 2023

Fate and mobility of PFAS in geomedia under saturated and unsaturated conditions: New insight on column experiments

Samuel Mertz
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Anne Togola
Julie Lions

Résumé

Purpose of study Poly- and perfluoroalkyl substances (PFAS) have become major emerging contaminants of concern due to their widespread occurrence in the environment and potential for human health impacts. A major interest is to understand their fate and mobility in environment, which is mainly controlled by sorption process in geomedia. PFAS sorption is dependent on PFAS molecular structure, geomedia physical and chemical properties and chemical properties of the aqueous solution. Column experiments have been used to quantify PFAS sorption albeit they have been mainly done in saturated conditions targeting PFAS sorption on solid-water interface (SWI) but preventing to assess adsorption reactions on air water interface (AWI). This lack of knowledge could prevent to understand correctly PFAS fate and mobility in soil and unsaturated zone of the aquifer. The aim of this study is to assess accurately dependence of PFAS sorption to geomedia saturation based on column experiment. Methodology The experiment were conducted with 4 PFAS (PFOA, PFOS, PFHxS and PFBS). Column experiments in saturated and unsaturated conditions were carried out on the two different geomedia (sand and a soil). To characterize the hydrodynamic properties of the two geomedia, experiments with a non-reactive tracer were done. A 10-2M CaCl2 solution was used as background electrolyte. For each saturation conditions, 2 stages have been carried out: injection of input solution with PFAS, ii) injection of free-PFAS input solution. Two PFAS concentrations were used in the input solution either 5 mg L-1 for each PFAS mimicking the ones encountered in contaminated soil and a lower PFAS concentration (5 µg L-1 for each PFAS) similar to environmental concentration. Analysis for PFAS compounds has been carried out using liquid chromatography mass spectrometry (LC-MS). Summary of findings/results At high PFAS concentration, PFAS sorption was similar in unsaturated and saturated conditions for the two geomedia. PFAS sorption could be neglected on sand. By contrast, sorption differs according to PFAS molecular structure in the soil. PFAS compounds with longer chain, notably PFOS, were more sorbed. PFAS with longer carbon chain interact more with clay minerals and organic matter. Comparison between unsaturated and saturated conditions highlighted that PFAS are mainly sorbed onto surface of solid phases and sorption at AWI could be neglected. At low PFAS concentration, saturation conditions as well as PFAS molecular structure impact their mobility in the two geomedia. PFAS with longer carbon chain were found to be sorbed on organic matter and clay minerals but also on quartz. Higher PFAS sorption was quantified under unsaturated conditions than in saturated conditions showing that sorption reactions on the AWI seem to play a key role at environmental PFAS concentration. This trend is greater for PFAS compounds with a longer carbon chain. Conclusion At high PFAS concentrations, values of the equilibrium constant coefficient depend on the amount of organic matter and clay material in soil and the carbon chain length of PFAS but saturation condition does not impact PFAS residence time. By contrast, sorption reaction onto SWI, hence saturation condition, are a main driver of PFAS mobility at low PFAS concentration. Compounds with the longer carbon chain are more sensitive. In addition, sorption of PFAS onto silicate minerals cannot be neglected at low PFAS concentration to assess correctly PFAS mobility. Significance / contributions of the study By demonstrating that PFAS sorption at AWI is concentration dependent, this study has improved understanding of PFAS mobility in unsaturated zone. The results reported herein highlight the value of conducting an integrated set of column experiments for investigating PFAS sorption processes and refine the conceptualization of PFAS mobility in environment.
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Dates et versions

hal-04190438 , version 1 (29-08-2023)

Identifiants

  • HAL Id : hal-04190438 , version 1

Citer

Nicolas Devau, Hugues Thouin, Mohamed Djemil, Samuel Mertz, Stéfan Colombano, et al.. Fate and mobility of PFAS in geomedia under saturated and unsaturated conditions: New insight on column experiments. AQUACONSOIL 2023, Sep 2023, Prague, Czech Republic. ⟨hal-04190438⟩
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