TITLE:
Thorium and Uranium Soil Profile Concentrations in Mississippi River Floodplains in Southeastern Missouri
AUTHORS:
Michael Aide
KEYWORDS:
Thorium, Uranium, Alluvium, Heavy Metals, Actinides
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.5,
May
19,
2026
ABSTRACT: In southeastern Missouri, the abundances of thorium and uranium were determined for two soil series in floodplains of the Mississippi River. The soils were Entisols and Inceptisols receiving annual flood inundation with alluvium accumulation. Aqua regia digestion provided thorium concentrations ranging from 4.4 to 10.3 mg?kg?1 across all soil horizons from all pedons. Similarly, aqua regia digestion provided uranium concentrations ranging from 0.4 to 1.1 mg?kg?1. The silty clay Inceptisol pedons manifested greater uranium concentrations than the sandy loam to silt loam Entisols. A Na-acetate leach was performed to estimate salt-displaceable thorium and uranium to ascertain relative availability for plant uptake and mobility. Thorium concentrations ranged from 18 to 66 μg?kg?1, whereas uranium concentrations ranged from 20 to 279 μg?kg?1. The aqua regia digestion concentrations and the pollution index values collectively suggest that these soils have not been environmentally impacted. Uranyl leaching or uranyl loss during river transport may have reduced the uranium concentrations.