Depleted uranium mobility and fractionation in contaminated soil (Southern Serbia)

Goal, Scope and Background During the Balkan conflict in 1999, soil in contaminated areas was enriched in depleted uranium (DU) isotopic signature, relative to the in-situ natural uranium present. After the military activities, most of kinetic DU penetrators or their fragments remained buried in the ground in certain geomorphological and geochemical environments exposed to local weathering conditions. The contamination distribution, mobility and/or fixation of DU in the contaminated soil profile at one hot spot were the subject of our study. The results should disclose what happened with released DU corrosion products in three years elapsed, given the scope of their geochemical fractionation, and mark out the most probable host substrates in investigated soil type. Methods Gamma-spectrometric analysis of soil samples taken in the DU penetrator impact-zone was done to obtain present contamination levels. Set of samples is subjected to five-step and three-step sequential extraction procedures, specifically selective to different physical/chemical associations in soil. The stable elements are determined in extracts by the atomic absorption spectroscopy. After the ion-exchange based uranium separation procedure, alpha-spectrometric analysis of obtained fractions was done and DU distribution in five extraction phases found from 235 U/ 238 U and 234 U/ 238 U isotopic ratios. Results Depleted uranium concentration falls down to the 1% of the initial value, at approximately 150 mm distance to the source. Carbonates and iron/manganese hydrous oxides are indicated as the most probable substrates for depleted uranium in the characterized soil type. Therefore, in the highly contaminated soil samples, depleted uranium is still weakly bonded and easy exchangeable. The significant levels of organic-bonded depleted uranium are found in surface soil only. Discussion Dependence of the fractionation on the contamination levels is evident. Samples with higher DU contents have shown a longer maintenance in the exchangeable phases, probably because adsorption/desorption mass transfer through the medium was not very fast. Organic-bonded, depleted uranium is present in surface soil samples due to its higher humus content. Considering geochemical composition of investigated soil, the indicating chemical associations as substrates are in agreement with some considerations based on the results for low-level waste unsaturated zones. Conclusions The soil contamination with depleted ur