Bacterial activation level determines Cd(II) immobilization efficiency by calcium-phosphate minerals in soil.

Soil mineral properties significantly influence the mobility of Cd(II) within the soil matrix. However, the limited understanding of how microbial metabolism affects mineral structure at the microscale poses challenges for in situ remediation. Here, we designed a model calcium-phosphate system in a urea-rich environment to explore the impact of different microbial activation levels on Cd(II) fixation at mineral interfaces. Findings indicate that bacteria affected the morphological structure of the minerals and the amount of carbonate incorporation (average 5.4 %), thereby enhancing Cd(II) immobilization capacity (up to 9.6 times). This process is influenced by the intensity of bacterial activation, as reflected in their urease activity. Extracellular substances secreted by bacteria are also essential for activating minerals, contributing to a sustained decrease in their surface potential. The introduction of activated minerals in potting experiments markedly stimulated the soil urease activity, promoting the enrichment of functional bacteria and facilitating Cd(II) passivation, thereby reducing Cd(II) uptake by vegetables. An extensive soil survey further corroborated a linkage between soil total phosphorus and urease activity, indirectly emphasizing the universality of phosphate mineral-urease microbial interactions and their critical role in the morphological transformation of Cd(II). Our findings highlight the functional dynamics of urease microorganisms in shaping soil mineral landscapes and regulating heavy metal mobility, with broad implications for soil microscale remediation strategies.