Activation of periodate driven by the synergistic interaction between inherent soil Fe and organic matter for adiazine degradation: Mechanisms, soil-type effects, and soil property changes.

Periodate (PI) has been extensively utilized for the degradation of recalcitrant organic pollutants in aqueous environments. In contrast, its application in soil remediation is still limited. The critical unknowns notably encompass whether, how, and to what extent inherent soil constituents activate PI. Here, we firstly demonstrate that inherent soil components, particularly Fe species and soil organic matter (SOM), can effectively activate PI without external catalysts. Using adiazine (ADZ) as a model, PI-mediated oxidation was systematically evaluated in 10 representative soils. Correlation analyses identified free Fe oxides (Fef) as the dominant PI activators, accounting for 79.06% of the overall ADZ degradation and driving the formation of reactive species (RS), including 1O2 (dominant), •IO3, •IO4, and •OH. SOM exhibited a component-dependent dual effect, promoting ADZ degradation in SOM-poor soils (33.77%) but inhibiting it in SOM-rich soils (-18.87%). Specifically, soluble microbial by-product-like and humic acid-like components facilitated RS generation, whereas aromatic protein and fulvic acid-like components suppressed RS generation by competing for PI. Spectroscopic analyses confirmed that PI treatment preserved soil structural integrity with only minor alterations. 11 transformation products and 3 degradation pathways were identified, and ecotoxicity analysis and phytotoxicity tests demonstrated reduced post-remediation toxicity and recovery of plant growth. Cl-, NO3-, and humic acid had no significant impact, whereas low concentration Fe3+ and Mn2+ enhanced oxidation. Overall, this study elucidates how inherent Fe oxides and SOM regulate PI activation in soils, providing a theoretical basis for optimizing in-situ PI oxidation for antibiotic-contaminated soils.