Sources and Variability of Plutonium in Chinese Soils: A Statistical Perspective with Moving Average

We investigated the different sources and their corresponding impact areas of Pu in Chinese surface soils to illustrate the state-of-the-art of the sources, levels and distributions of Pu-24(0)/Pu-239 atom ratios as well as Pu-239/(PU)-P-24-P-0 activity concentrations in China. For the first time a moving average strategy in combination with statistical analysis was employed to partition geographic areas in China based on the reported Pu-24(0)/Pu-239 atom ratio and Pu-239/(PU)-P-24-P-0 concentration data from public literature. During the partitioning, the median (MED) of the dataset was basically employed as a criteria in place of the commonly used arithmetic average (AM). Concisely, three areas were partitioned according to the different influences of Pu from the Lop Nor (LNTS) and Semipalatinsk (STS) test sites and the global fallout. The partitioned Ternary area (80 degrees E-105 degrees E, 35 degrees N-50 degrees N) was supposed to have multiple sources of Pu including the STS and LNTS besides the global fallout, which was characterized with slightly lower Pu-24(0)/Pu-239 atom ratios (MED = 0.174) as well as elevated Pu-239/(PU)-P-24-P-0 concentrations (MED = 0.416 mBq/g). Meanwhile, the Binary area (35 degrees N-45 degrees N, 100 degrees E-115 degrees E) was considered to have received the extra contribution from the high-yield nuclear tests at the LNTS besides the global fallout, resulting in the highest Pu-24(0)/Pu-239 atom ratios (MED = 0.200) across China. The remaining area was marked as the Unitary area, where it only received the exclusive contribution of global fallout. Furthermore, through the statistical analysis of the Pu-24(0)/Pu-239 data in the Unitary area, we recommended a value of 0.186 +/- 0.021 (AM +/- SD) as a representative or area-specific Pu-24(0)/Pu-239 atom ratio baseline to characterize the global fallout derived Pu in Chinese soils.