New insight into the contribution of humic substance to degradation of phthalate acid esters in soil: Link batch experiment to model study

Degradation of PAEs influenced by humic substance (HS) is a fundamental biological/chemical process happened in soil. It was commonly believed that the sequestration of PAEs by HS is the dominant mechanism. However, by far, detail relationships between bioavailability of HS-PAEs complex and degradation behavior of PAEs still remains unclear. For this, the effect of HA and FA on degradation of PAEs were investigated by batch experiment in our work. The interactions between HA/FA and DBP were examined using fluorescence spectroscopy. Microcalorimetry combined with QSAR model analysis were applied to assess bioavailability of HS-PAEs complex and further interpret the effect of HS on degradation of PAEs. The results indicated that the complex formed between DBP and HA inhibit the metabolic activity in soil while opposite effect was found for FA-PAEs complex, which were sensitively reflected by the heat power. In addition, traditional 2D-QSAR model coupled with 3D contour maps highlight the mutual effects of quantum chemical parameters and HS on degradation of PAEs in soil, and further proved that bioavailability of HA/FA-PAEs complex were responsible for controlling the degradation rate in soil. This study provides interesting new insights in the effect of HS on degradation of PAEs in soil.