Spatial distribution and migration of 239+240Pu in Chinese soils
2022
Huang, Yanan | Sun, Xiaoming | Zhang, Wei | Xiao, Zhi
The migration of radionuclides is a critical threat to the soil and groundwater environment. This study investigates highly radiological toxic ²³⁹⁺²⁴⁰Pu in 647 surface soils and 66 soil cores in China. First, the spatial distributions of ²³⁹⁺²⁴⁰Pu activities and ²⁴⁰Pu/²³⁹Pu ratios are presented in Chinese surface soils. Second, four different types of vertical distribution of ²³⁹⁺²⁴⁰Pu, namely 45.4%, 40.9%, 9.1% and 4.5% of Chinese soil cores proportions are integrated using statistical analysis. Furthermore, different soil types are accompanied by different ²³⁹⁺²⁴⁰Pu vertical distributions, which relate closely to the ²³⁹⁺²⁴⁰Pu migration. Finally, based on the Convection Dispersion Equation (CDE) model, the present work find that the apparent convection velocities of ²³⁹⁺²⁴⁰Pu are ranging from 0.00032 ± 0.00031 cm a⁻¹ to 0.473 ± 0.083 cm a⁻¹. As shown by the four typical vertical activity distribution of ²³⁹⁺²⁴⁰Pu in soil cores, the deepened activity maximum value position of ²³⁹⁺²⁴⁰Pu implies a fast migration rate or apparent convection velocity. This study, for the first time, suggests a significant linear correlation (R² = 0.847) between the depth of ²³⁹⁺²⁴⁰Pu maximum value (cm) and the apparent convection velocity (v, cm a⁻¹). We hypothesize that v usually does not exceed 0.5 cm a⁻¹ in the CDE model. A significant linear correlation is also identified between apparent dispersion coefficient (D, cm² a⁻¹) and v² in Chinese soil cores from the CDE model. It will provide an important reference for harmful heavy metal migration research in the future.
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