Aqueous and Colloidal\nDynamics in Size-Fractionated\nPaddy Soil Aggregates with Multiple Metal Contaminants under Redox\nAlternations

Soil contamination by multiple metals is a significant\nconcern\ndue to the interlinked mobilization processes. The challenges in comprehending\nthis issue arise from the poorly characterized interaction among different\nmetals and the complexities introduced by spatial and temporal heterogeneity\nin soil systems. We delved into these complexities by incubating size-fractionated\npaddy soils under both anaerobic and aerobic conditions, utilizing\na combination of techniques for aqueous and colloidal analysis. The\ncontaminated paddy soil predominantly consisted of particles measuring\n<53, 250–53, and 2000–250 μm, with the <53\nμm fractions exhibiting the highest concentrations of multiple\nmetals. Interestingly, despite their higher overall content, the <53\nμm fractions released less dissolved metal. Furthermore, glucose\nenhanced the release of arsenic while simultaneously promoting the\nsequestration of other metals, such as Pb, Zn, and Cu. Utilizing asymmetric\nflow field-flow fractionation, we unveiled the presence of both fine\n(0.3–130 kDa) and large (130–450 nm) colloidal pools,\neach carrying various metals with different affinities for iron minerals\nand organic matter. Our results highlighted the pivotal role of the\n<53 μm fraction as a significant reservoir for multiple metal\ncontaminants in paddy soils, in which the colloidal metals were mainly\nassociated with organic matter. These findings illuminated the size-resolved\ndynamics of soil metal cycling and provided insights for developing\nremediation strategies for metal-contaminated soil ecosystems.