Differentiated responses of dissolved organic matter molecular properties in surface and bottom soil layers to...

This study investigated the spatial differentiation characteristics of the molecular properties of soil dissolved organic matter (DOM). The distribution patterns of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in the surface and bottom layers of typical soil samples were analyzed, and evaluated the interactions among DOM, microbial communities, and PFASs via multi-dimensional analyses. Results revealed distinct DOM stratification: surface soils contained microbially derived, bioactive low-molecular-weight components, while deeper soils showed more aromatic (SUVA254 ≈ 1.0) and humified DOM. Short-chain PFASs (PFHxA: 0.77-4.1 ng g⁻¹) exhibited "surface enrichment-bottom attenuation" distribution, strongly correlating with DOM characteristics. Microbial analysis identified Proteobacteria and Ascomycota as key regulators, with surface degradation and deep-layer DOM-PFASs complexation dominating respectively. Structural equation modeling demonstrated soil pH, nitrogen and carbon indirectly influenced PFASs distribution via DOM modification. The proposed "DOM-microbial functions-pollutant behaviors" model challenges conventional PFASs behavior understanding and provides critical parameters for ecological risk assessment. These findings establish a theoretical basis for stratified "surface bioenhancement-bottom chemical fixation" remediation technology, offering significant implications for new pollutant control and safeguarding ecological/water source security. Overall, this study has significant practical value for improving the control strategies of new pollutants and ensuring regional ecological security and the safety of drinking water sources.