Distribution and Fractionation of Uranium in Weapon Tested Range Soils

Abstract

Uranium is a chemically toxic and radioactive heavy metal. Depleted uranium (DU) is the byproduct of the uranium enrichment process, with a majority of U as uranium-238, and a lower content of the fissile isotope uranium-235 than natural uranium. Uranium-235 is mainly used in nuclear reactors and in the manufacture of nuclear weapons. Exposure is likely to have an impact on humans or the ecosystem where military operations have used DU. Yuma Proving Ground in Arizona, USA has been using depleted uranium ballistics for 36 years. At a contaminated site in the Proving Grounds, soil samples were collected from the flat, open field and lower elevated trenches that typically collect summer runoff. Spatial distribution and fractionation of uranium in the fields were analyzed with total acid digestion and selective sequential dissolution with eight operationally defined solid-phase fractions. In addition to uranium, other trace elements (As, Ba, Co, Cr, Cu, Hg, Mo, Nb, Pd, Pb, V, Zn, Zr) were also assessed. Results show that the trench area in the testing site had a higher accumulation of total U (12.4%) compared to the open-field soil with 279 mg/kg U. Among the eight solid-phase components in the open-field samples, U demonstrated stronger affinities for the amorphous iron-oxide bound, followed by the carbonate bound, and the residual fractions. However, U in the trench area had a stronger binding to the easily reducible oxide bound fraction, followed by the carbonate-bound and amorphous iron-oxide-bound fractions. Among other trace elements, Nb, As, and Zr exhibited the strongest correlations with U distribution among solid-phase components. This study indicates a significant spatial variation of U distribution in the shooting range site. Fe/Mn oxides and carbonate were the major solid-phase components for binding U in the weapon test site.

Coupling Electrokinetics and Phytoremediation to Remove Uranium from Contaminated Soil: A Laboratory Pilot-Scale Study

“…U occurs in a wide range of valence states. Two states predominate in near-surface environments: tetravalent uranium, U­(IV), and hexavalent uranium, U­(VI). , Under oxidizing conditions, U is primarily present in its hexavalent state as a uranyl cation (UO 2 2+ ). , The major U minerals in soils with DU penetrators and penetrator fragments were schoepite (UO 3 ·2.25H 2 O), dehydrated schoepite (UO 3 ·0.75H 2 O), and metaschoepite (UO 3 ·2H 2 O). , Thus, three major U forms (UO 2 , UO 3 , and uranyl) were used in this study. Analytically pure-grade uranyl nitrate UO 2 (NO 3 ) 2 , uranium trioxide UO 3 , and uranium dioxide UO 2 were added at the 100 mg U kg –1 level to the soil.…”

“…The correlation between water-extractable/exchangeable U in the rhizosphere and plant U in shoots/roots was analyzed. In addition, U fractionation was conducted according to the revised sequential selective dissolution procedure by Tessier et al ,, …”

“…Large stocks of DU have been generated as a result of the enrichment operations, especially in the United States . In recent years, the use of DU weapons such as DU-containing penetrators has resulted in U contamination in soil and water on ranges. − Uranium is often present in phosphate minerals, leading to the contamination of commercial products such as gypsum and phosphate (P) fertilizers . It was reported that the average U concentrations were between 6 and 149 mg/kg U in P-containing mineral fertilizers, while the U concentrations in mineral fertilizers without P were below 1.3 mg/kg U .…”

A laboratory preparation procedure for studying bioaccumulation of U and its subcellular form in earthworms (Diplocardia spp.)

“…DU was used in military applications such as armor-piercing projectiles known penetrators and for armor-plating tanks based on its pyrophoric properties and high density. Several hundred tons of DU were released in military conflicts over the past forty years and DU was expected to remain in battlefields and army testing sites [3] , [4] , [5] , [6] , [7] . We previously reported that significant U was accumulated in army weapon test sites – Yuma Proving Ground site [5] , [6] , [7] .…”

“…Several hundred tons of DU were released in military conflicts over the past forty years and DU was expected to remain in battlefields and army testing sites [3] , [4] , [5] , [6] , [7] . We previously reported that significant U was accumulated in army weapon test sites – Yuma Proving Ground site [5] , [6] , [7] . In the fields of Yuma Proving Ground, 92.8% of U from DU penetrators and fragments remained in the top 5 cm of soil and decreased to background concentrations in less than 20 cm [7] .…”