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J. Environ. Qual
Vol. 33, No: xx, 2004; Pages: 2070–2077


Mechanisms of Thorium Migration in a Semiarid Soil

A. J. Bednar,* D. B. Gent, J. R. Gilmore, T. C. Sturgis, and S. L. Larson

United States Army Corps of Engineers, ERDC, Environmental Laboratory, Vicksburg, MS 39180.

Abstract

Thorium concentrations at Kirtland Air Force Base training sitesin Albuquerque, NM, have been previously described; however, themechanisms of thorium migration were not fully understood. This work describes the processes affecting thorium mobility in this semiarid soil, which has implications for future remedial action. Aqueousextraction and filtration experiments have demonstrated the colloidalnature of thorium in the soil, due in part to the low solubility ofthorium oxide. Colloidal material was defined as that removed by a0.22-mor smaller filter after being filtered to nominally dissolved size(0.45 m). Additionally, association of thorium with natural organicmatter is suggested by micro- and ultrafiltration methods, and electrokinetic data, which indicate thorium migration as a negatively chargedparticle or anionic complex with organic matter. Soil fractionationand digestion experiments show a bimodal distribution of thorium inthe largest and smallest size fractions, most likely associated withdetrital plant material and inorganic oxide particles, respectively.Plant uptake studies suggest this could also be a mode of thoriummigration as plants grown in thorium-containing soil had a higherthorium concentration than those in control soils. Soil erosion laboratory experiments with wind and surface water overflow were performed to determine bulk soil material movement as a possible mechanism of mobility. Information from these experiments is being usedto determine viable soil stabilization techniques at the site to maintaina usable training facility with minimal environmental impact.

Keywords:micro;ultrafiltration methods;electrokinetic data;thorium-containing soil;Thorium Migration;Semiarid Soil;radionuclide.


Corresponding author:

E-mail: J.Bednar@erdc.usace.army.mil

 

 
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