Long-term distribution and vertical migration of plutonium in a peat profile after the 1993 Siberian Chemical Combine...

In 1993, a radiological accident at the Siberian Chemical Combine resulted in a persistent radioactive trace northeast of the Radiochemical Plant, raising long-term concerns about radionuclide mobility in the environment. Among the long-lived radionuclides remaining in soils, plutonium-239 (²³⁹Pu) is of particular interest due to its high toxicity and complex environmental behavior. This study determined the distribution and dominant forms of plutonium more than a quarter century after the fallout. A rapidly growing stratified peat bog was subdivided into age horizons based on excess lead-210 (²¹⁰Pb), which enabled confirmation of vertical migration of plutonium. Alpha Track radiography revealed that over half of the plutonium released during the accident remains trapped within low-solubility 'hot' particles. Data point to the gravitational vertical migration appears to involve small plutonium-bearing particles formed by the degradation of the original fallout material. These findings emphasize the key role of the initial chemical and physical forms of plutonium in governing its long-term environmental fate.