Unveiling Molecular Transformations of Soil Organic Matter after Remediation by Chemical Oxidation Based on ESI-FT-ICR-MS analysis

Abstract

Remediation of soils contaminated with organic pollutants is often accomplished by chemical oxidation processes using oxidants such as persulfate or H2O2. However, it is unclear how different oxidants transform soil organic matter (SOM) and affect soil ecosystem services. Herein, two chemical oxidation technologies, Fenton reaction (FT) and base-activation of sodium persulfate (BP), were investigated to remediate diesel-polluted soils. The molecular transformation of SOM was analyzed using excitation–emission matrix fluorescence spectroscopy (EEM FS) and electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Fulvic acid-like substances and lipids were consumed in both treatments, while the contents of lignin-like and tannin-like substances increased after BP treatment. The oxygen to carbon ratios (O/C), modified aromaticity index (AImod), and double bond equivalent (DBE) of SOM increased significantly in BP-treated soil, while these parameters decreased in FT-treated soil (FTS), suggesting the oxygen-containing, unsaturated and aromatic compounds were produced in BPS but removed in FTS. The increased cation exchange capacity (CEC) value (81.47 cmol/kg) and germination index of wheat seed (97%) for the SOM in BPS indicate the possible favorable effect of persulfate-based treatment on soil quality. Overall, this study advances mechanistic understanding of the effects of H2O2- and persulfate-based soil remediation technologies based on the molecular compositions of SOM and soil quality.