Regulatory patterns and driving factors of soil aggregates on the environmental behavior of heavy metals: A global study based on meta-analysis and machine learning.

Soil heavy metal (HM) pollution poses a global threat, yet the aggregate-governed relationships and mechanisms linking HM adsorption, distribution, and remediation remain unclear. This study clarifies the dominant role of soil aggregates in controlling HM fate, specifically targeting the aggregate-driven pathway of adsorption-desorption-migration-transformation. Compared to macroaggregates, the effect percentage (EP) of microaggregates on adsorption was 21.63%, and the EP on desorption was -16.78%. The HMs in microaggregates are mainly stabilized through specific adsorption, complexation and physical encapsulation, resulting in a relatively low proportion of available forms such as exchangeable state (EP = -5.03%) and carbonate-bound state (EP = -19.67%). On the contrary, although the total HM content in macroaggregates is relatively low, their loose porous structure, HM fixation mode and active microbial interface jointly contribute to higher availability. The total content of HM in microaggregates was relatively high (EP = 4.77%), while the available content of HM in macroaggregates was significantly higher than that in microaggregates (EP = -8.88%). Consequently, macroaggregates demonstrated superior remediation effectiveness for HMs. The EP of the total HMs is 12.63%, and the EP of the availability HMs is 12.54%. Machine learning (RF, XGBoost, LightGBM) identified HM type, soil organic matter, and pH as key controls over HM adsorption and distribution. These factors directly govern HM bioavailability and mobility, and are mediated by soil aggregate stability and regulation. This study elucidates aggregate-driven mechanisms linking HM adsorption, distribution, and remediation, offering a scientific basis for targeted pollution control and soil restoration while proposing a new perspective for international cooperation in contamination management.