Vertical distribution of Pu in forest soil in Qinghai-Tibet Plateau

摘要

The Pu239+240 and Cs-137 activities and Pu-240Pu/239 atom ratios in surface soil and soil core collected from Qinghai-Tibet Plateau were investigated. The maximum of Pu239+240 and Cs-137 activity concentrations in five soil cores were found in upper layers and have a same trend: the maximum followed by exponential decline. The Pu-240/Pu-239 atom ratio ranged from 0.160 +/- 0.009 to 0.212 +/- 0.012, clarified that the plutonium mainly came from the global fallout and the contribution of Lop Nor test sites was negligible. In addition, the vertical profiles of radionuclides (Pb-210, U-238, Th-232, Ra-226, K-40) have been studied and a high correlation has been found between them. The correlations of Pu between organic matter (OM) and heavy metals were also studied. Person Correlation Coefficients revealed Pu had significant positive correlations with organic matter and Cd, Cu, Co, Zn, but negative correlation with Tl. The results have important implication for further understanding of the sources, records and environmental impacts of global and regional nuclear activities, which expanded the database of Pu activity level and atom ratio in Chinese soil and established a foundation for future environmental risk assessment.