Uranium release from iron-rich acid soils under IPCC elevated CO₂ scenarios: One-sided organic nanocolloidal...

The global iron-rich acid soils, containing ppm uranium (U), support a population of billions. Because of high sensitivity of U to dissolved inorganic carbonates (DIC), global CO₂ rising may significantly influence mobility of U in soils. However, responses of U release and fractionation between various colloidal and dissolved phases to elevated CO₂ (eCO₂) were unknown. In this study, we unveiled U release behavior and underlying mechanisms in the latosol and black soils upon exposure to simulated eCO₂ using edge-cutting nanoscale IR spectroscopic mapping (NanoIR mapping) and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), combined with uranyl speciation analysis and simulation. The eCO₂ treatment significantly decreased soil pH, disintegrated soil aggregates, and caused substantial release of U. Soil acidification, rather than DIC change, governed U release and fractionation. Upon eCO₂ exposure, U was leached from soils predominantly (>90 %) in organic nanocolloidal phases, contrasting with the widely recognized iron oxide-colloidal phase in iron-rich acid soils. The dominant organic nanocolloidal U could be ascribed to the direct release of U-loaded organic nanocolloids during disintegration of organic-mineral complexes. These results imply the continuous global CO₂ rise may significantly amplify environmental and health risks of U in acid soils by significantly increasing its mobility.