Long-term corrosion and leaching of depleted uranium (DU) in soil

Corrosion and leaching of depleted uranium (DU) was investigated for 3 years using six DU munitions (145-264 g DU) each buried in a column with a soil core of about 3.3 kg dry soil mass. The columns were installed in an air-conditioned laboratory. Each week they were irrigated and U-238 was determined in the effluents by inductively coupled plasma mass spectrometry. In addition, U-238 was measured occasionally to assure that the U-238 was predominantly from the DU munition. On average, 14.5 g corresponding to 7.9% of the initial DU mass was corroded after 3 years, indicating an increased corrosion as compared to the first year of observation. The leaching rates increased much stronger than the corrosion rates by factors of more than 100, resulting in a mean total amount of leached U-238 of 13 mg as compared to 0.03 mg after the first year. Uranium species identified in the seepage water by time-resolved laser-induced fluorescence spectroscopy were mainly hydroxo and carbonate compounds, while those in the corroded material were phosphate compounds. It is concluded that the dramatic increase of the leaching and its large temporal variability do not allow any extrapolation for the future. However, the high U-238 concentrations observed in the seepage water highlight the need for further investigations on the transport of U-238 through soil, in particular with regard to the potential future U-238 contamination of groundwater in areas affected by DU weapons.