Depleted uranium migration in soil vadose zone due to a corroded penetrator of former armed conflicts

Corrosion of depleted uranium (DU) in armor penetrators can lead to DU contamination of soil and groundwater. This is a serious environmental problem at former theatres of war where DU penetrators had been used. However, literature on such DU migration is still scant. In the present study, a soil profile underneath a penetrator that had corroded over 7 y in Bosnia and Herzegovina was investigated. The highest concentration of DU was ~45,300 mg/kg in the layer immediately beneath the penetrator. But the concentration decreased rapidly in deeper soil layers. As a result, most (99.9%) of the released DU was within the 17 cm beneath the penetrator. Using electron microscopy, we found that the DU was primarily in the form of detrital U mineral particles near the penetrator (0-15 cm), and was mainly present as soluble form adsorbed on clay minerals and iron oxides in deeper soil layers (15-50 cm). Combining synchrotron-based X-ray microscopy (XFM) and micro-scale X-ray absorption spectroscopy (μ-XAS) analyses, we showed that the DU in the soil profile was mostly hexavalent, consistent with the oxic conditions of the vadose zone. Overall, this work revealed that the DU migration rate in the soil vadose zone was relatively slow. However, DU would eventually reach the underlying aquifer and pose a serious long-term risk, if the penetrator had been left in soil for decades.