Evolution of soil DOM during thermal remediation below 100 °C: concentration, spectral characteristics and complexation ability

The impact of thermal remediation on soil function has drawn increasing attention. So far, as the most active fraction of soil organic matter, the evolution of dissolved organic matter (DOM) during the thermal remediation lacks in-depth investigation, especially for the temperatures value below 100 °C. In this study, a series of soil thermal treatment experiments was conducted at 30, 60, and 90 °C during a 90-d period, where soil DOM concentration increased with heating temperature and duration. The molecular weight, functional groups content and aromaticity of DOM all decreased during the thermal treatment. The excitation-emission matrices (EEM) results suggested that humic acid-like substances transformed into fulvic acid-like substances (FIII/FV increased from 0.27 to 0.44) during the heating process, and five DOM components were further identified by EEM-PARAFAC. The change of DOM structures and components indicated the decline of DOM stability and hydrophilicity, and can potentially change the bioavailability and mobility. Elevated temperature also resulted in the decline of DOM complexation ability, which may be caused by the loss of binding sites due to the decrease of polar function groups, aromatic structures and hydrophilic components. This study provides valuable information about the evolution of DOM during thermal remediation, which would potentially change the fate of metal ions and the effectiveness of the post-treatment technologies in the treated region.