Due to the high radiotoxicity in high concentration of α emitting ²³⁹Pu (T_1/2 = 24,100 yr) and 240Pu (T_1/2 = 6561 yr), and the fingerprint information of source terms carried by ²⁴⁰Pu/²³⁹Pu atomic ratios, the level and sources of ^239,240Pu in the environment is of great significance in the view of radiation risk. Meanwhile, the environmental behaviors, including deposition, retention and migration of plutonium are also important in the investigation of their potential hydrosphere contamination, uptake by flora and fauna and transfer to food chain.

However, such research in the Qinghai-Tibet Plateau is still missing, where is deemed as an environmental sensitive area. Researchers from the environmental radioactive team in the Institute of Earth Environment, Chinese Academy of Sciences collected surface soil samples from the Qinghai-Tibet Plateau and first analyzed ^239,240Pu concentrations and ²⁴⁰Pu/²³⁹Pu ratios in this area.

They found that the concentrations of ^239,240Pu were in the range of 0.0176–1.95 Bq/kg, falling into the reported ranges in the background areas from the similar latitude belt. The ²⁴⁰Pu/²³⁹Pu atomic ratio range was measured to be 0.146–0.225, which was similar with the global fallout values. Both indicate that the stratospheric fallout from global atmospheric nuclear weapons tests is the major radioactive source in this region, and the low plutonium level will not cause any radiation risk so far. 

Based on the statistical analysis of all the possible parameters influencing the spatial distribution characteristics of ^239,240Pu concentrations, including soil organic content, soil moisture content, average annual precipitation, altitudes, topography and human activity, the large variations of ^239,240Pu concentrations were mainly attributed to the retention process related factors including soil organic content and human activity disturbances. While, the deposition related factors including the average annual precipitation, altitudes, topography made insignificant influence due to the low ^239,240Pu concentrations in atmosphere, less wet deposition amount and low re-suspended amount. The highest ^239,240Pu concentrations of 0.805–1.95 Bq/kg were mainly due to the good retention condition in the sampling sites with higher soil organic content and less human activity disturbances.

This work, published in  Environmental Pollution, was financially supported by the Chinese Academy of Sciences (No. XDB40020100, 132B61KYSB20180003), the Natural Science Foundation of China (No. 41991252, 11875261), and the State Key Laboratory of Loess and Quaternary Geology (No. SKLLQG1942).