NMR spectroscopy and MRI for revealing the interactions of PFAS with soil

The internship will take place across two laboratories in Nantes: the LEE at Gustave Eiffel University for sample preparation and characterization, and the CEISAM at the Nantes University for NMR development and experiments.

Context:

Poly- and perfluoroalkyl substances (PFAS), known as “forever chemicals”, form a family of more than 4000 molecules used in a wide range of industrial, agricultural and domestic applications^[1]. Most of these substances are toxic, persistent in the environment and bioaccumulative.

To improve the understanding of the behavior of PFAS in soils, batch experiments (adsorption and desorption kinetics or isotherms) are used to determine the sorption properties of a subset of these molecules in natural and model porous media^[2–5], allowing to better understand the interactions of PFAS with both organic and mineral components of soil. However, soils and contaminants are usually studied by conventional chemical extraction and adsorption essays prior to and at the final state of contamination with no information about contaminant behaviour at the pore scale^[6]. The difficulty to understand PFAS and soil components interactions is further exacerbated when working with samples containing “PFAS cocktails”, which are known to increase single PFAS danger.

Objectives and programme:

Under this context, the proposed internship project focusses on the development and application of Nuclear Magnetic Resonance (NMR) for deciphering PFAS-soil interactions from atomic to macroscopic scales. With this aim, NMR relaxometry, spectroscopy and imaging (MRI) methods will be combined to investigate the behaviour of PFAS mixtures in different kind of soils:

1) In particular, the student will be involved in the measurement of ¹⁹F diffusion (D) coefficients and T₂ relaxation times^[7] for revealing PFAS interactions in soil. Different T₂ and D values are expected depending on the environment especially if PFAS are free in solution or under weak, medium or strong interactions with the constituents of soil.

2) To track the movement and adsorption of PFAS in different compartments (i.e. supernatant, soil) of the sample, the student will record 1D MRI profiles, chemical shift imaging as well as slice selective experiments to macroscopically localize selected PFAS of the cocktail in different compartments of soil.

3) In order to decipher interactions of each PFAS of a mixture in the multiphasic compartments of a soil, it becomes essential to merge relaxometric, diffusional and imaging methods. Thus, the development of novel approaches will allow for linking chemical and macroscopical data.4) Sate of the art (see 1, 2) and developed NMR methods (see 3) will be applied to PFAS with different chain lengths (C4 to C12) and also a newly marketed molecule (GenX). PFAS will be dissolved in soils of increasing complexity. First, only the mineral part of soil such as Fontainbleau sand will be used to mimic the porous network of soil. Then, natural organic matter (NOM) from the International Humic Substances Society will be used as a model of soil organic matter. Finally, NOM and sand will be mixed to have a more realistic soil.*

References:

[1]            Z. Wang, J. C. DeWitt, C. P. Higgins, I. T. Cousins, “A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)?” Environ. Sci. Technol. 2017, 51, 2508–2518.

[2]            C. P. Higgins, R. G. Luthy, “Sorption of Perfluorinated Surfactants on Sediments” Environ. Sci. Technol. 2006, 40, 7251–7256.

[3]            Q. Yu, R. Zhang, S. Deng, J. Huang, G. Yu, “Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: Kinetic and isotherm study” Water Research 2009, 43, 1150–1158.

[4]            F. Xiao, B. Jin, S. A. Golovko, M. Y. Golovko, B. Xing, “Sorption and Desorption Mechanisms of Cationic and Zwitterionic Per- and Polyfluoroalkyl Substances in Natural Soils: Thermodynamics and Hysteresis” Environ. Sci. Technol. 2019, 53, 11818–11827.

[5]            S. Mejia-Avendaño, Y. Zhi, B. Yan, J. Liu, “Sorption of Polyfluoroalkyl Surfactants on Surface Soils: Effect of Molecular Structures, Soil Properties, and Solution Chemistry” Environ. Sci. Technol. 2020, 54, 1513–1521.

[6]            J. G. Longstaffe, D. Courtier-Murias, A. J. Simpson, “The pH-dependence of organofluorine binding domain preference in dissolved humic acid” Chemosphere 2013, 90, 270–275.

[7]            D. Courtier-Murias, E. Michel, S. Rodts, F. Lafolie, “Novel Experimental–Modeling Approach for Characterizing Perfluorinated Surfactants in Soils” Environ. Sci. Technol. 2017, 51, 2602–2610.

Profile:

We are looking for a motivated master 2 or engineer student in (bio)chemical analysis or chemical physics with ideally a previous experience in NMR and interested in environmental sciences.

This internship may also lead to a PhD opportunity on NMR developments aimed at understanding the interactions between emerging contaminants (e. g. nanoparticles and PFAS) and soils within the framework of the ANR COMMON project.