Distribution of Uranium and Thorium in Soil and Woody Plants of Eastern Siberia (Irkutsk Region)

Abstract

Uranium and thorium contents in soils and plants of pine forests on the south of Eastern Siberia were investigated. This region is a major wood supplier, therefore the survey of radioactive elements concentration in wood is a subject of practical interest. Concentrations of uranium and thorium were determined in soil samples, in trees (aboveground parts and roots of Pinus sylvestris, Larix sibirica, and Betula pendula), and in ground cover plants. Samples analysis included ashing, dissolution in nitric acid, extraction of radionuclides by tributylphosphate, ion-exchange separation, and measurement of radioactivity with liquid scintillation counter 1219 RackBeta-Spectral. The major characteristic of all studied ecosystems was that the highest thorium and uranium concentrations in the ash of various parts of the forest forming species (pine and larch) were measured in roots; the lowest concentrations were in needles. Radionuclides concentrations in the ash from the trees growing on the soddy-podzol soils were noticeably higher than that from the trees growing on the soddy-forest soils. The average uranium content ranged from 1.44 to 2.72 mg kg-1 in the soils of the studied region and from 0.049 to 0.169 mg kg-1 in the wood ash. The average thorium content reached 4.18 – 8.23 mg kg-1 in the soils and 0.146-0.767 mg kg-1 in the plants ash. The average contents of uranium and thorium in the ash of the ground cover plants were from 0.046 to 0.387 mg kg-1 and from 0.205 to 0.515 mg kg-1, respectively

Keywords

• Pine forests
• Eastern Siberia
• uranium
• thorium
• distribution in soil and wood