Spatial distribution, speciation, and release behavior of exogenous copper in soil aggregates: The role of aggregate...

Copper (Cu) contamination in soil poses serious environmental risks, impacting ecosystem health and groundwater quality. This study explored how soil aggregate structural reorganization influences the spatial distribution, chemical speciation, and release behavior of exogenous Cu. Aggregates with and without structural reorganization were prepared. Cu distribution was analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), speciation via sequential extraction procedures (SEP), and release kinetics through stirred-flow experiments. Non-reorganized aggregates (Ext-aggregates) showed pronounced sub-millimeter Cu fluctuations, while reorganized ones (Mix-aggregates) exhibited more homogeneous Cu distribution due to enhanced mixing. Over a 62-day incubation, Cu heterogeneity in Ext-aggregates decreased, approaching that of Mix-aggregates. SEP results showed rapid stabilization of Cu within 1-day, with Mix-aggregates retaining more Cu in residual fractions and less in labile fraction. Stirred-flow experiments revealed a time-dependent decline in Cu release, with Mix-aggregates consistently releasing less Cu than Ext-aggregates. A kinetic model incorporating the proportion of Cu-contacted subregions effectively simulated Cu release dynamics. These findings highlight the potential of soil structural management practices, such as tillage and organic amendments, to mitigate Cu leaching. Moreover, the inclusion of the mixing parameter f₁ provides a quantitative framework for improving predictions of Cu mobility and ecological risk in dynamic soil systems.