Effects of ozonation on the molecular signatures of soil organic matter: Transformations and mechanisms

Ozonation is a feasible chemical oxidation remediation technology for soils contaminated with organic pollutants. Nevertheless, little is known about the influence of ozonation on soil organic matter (SOM) at the molecular level, which is crucial for the sequestration of contaminants and the functional restoration of soil. In this study, SOM extracted from an organically contaminated site was analyzed by mass spectrometry and spectral combined techniques to investigate its transformation during ozonation. SEC-DAD-FLD-OCD analysis showed that macromolecular components were significantly reduced, and the major components changed from humic acid-like substances to building blocks of humic substances. FT-ICR-MS analysis showed that the CHON, CHONS compounds decreased as a result of ozonation. Lignin-like compounds remained the dominant component throughout. The molecular unsaturation and aromaticity significantly decreased during ozonation. Ozonation changed the structural characteristics by introducing O, –H, and –CH 2 . Py-GC-MS analysis showed that PAHs components, benzene derivatives, and phenol components decreased during ozonation. The molecular markers, 4-vinylphenol, (2-methyl-1-methylenebutyl) benzene, originated from fresh lignin, are abundant in original SOM, while 2-phenyl cyclohexanone and biphenyl originated from condensed organic carbon, are retained during ozonation. Ozonation selectively destroyed constituents with aromatic rings. The sorption capacity of soil for PAH S decreases due to the transformation and loss of SOM. The ozonated water-soluble SOM is less conducive to seed germination than the SOM from not ozonated control soil. This study advances the mechanistic understanding of the conversion of (water-soluble) SOM during ozonation at the molecular level and the impacts on organic pollutants sequestration and soil quality. • The molecular weight and number of SOM decreased after ozonation. • The molecular unsaturation and aromaticity decreased after ozonation. • Ozonation changed SOM molecular signatures by introducing O, –H, and –CH 2 to SOM. • Four molecular markers based on Py-GC-MS were screened out. • Ozonation reduced the sorption of PAHs to soils.