-As (9.5-28.1%). These were accompanied by a redistribution of Cd from the exchangeable fraction (EX-Cd) toward more stable forms (CA-Cd, WOM-Cd, and OX-Cd), and by a reduction in Fe-As together with increases in AE-As and Al-As fractions. Total DOM content increased markedly upon FA addition, with substantial increases in humic-like (C1 and C2, 0.9-1.5-fold) and protein-like (C3, 1.3-3.7-fold) components. Furthermore, decreases in Fed (6.2-11.5%) and increases in Feo (6.2-25.9%) under reduction conditions were accelerated by FA amendment. Random Forest (RF) and Structural Equation Modeling (SEM) analysis consistently identified DOM components and Fe fractions as the dominant predictors of Cd / As availability. The relationships among DOM components, Fe oxide fractions, and metal availability suggest that the co-variation of DOM components and Fe fraction changes may contribute to reduced Cd availability. In contrast, the increased As mobility may be associated with Fe oxide reduction, DOM competitive interaction, and possible As valence transformation. These findings provide association-based evidence linking DOM composition, Fe fraction changes, and Cd / As behavior in flooded paddy soil.
Li et al. (Wed,) studied this question.