Fate of Plutonium at a Former Nuclear Testing Site in Australia

A series of the British nuclear tests conducted on mainland Australia between 1953 and 1963 dispersed long-lived radioactivity and nuclear weapons debris, the legacy of which is a long-lasting source of radioactive contamination to the surrounding biosphere. A reliable assessment of the environmental impact of these types of radioactive contaminants and their implications for human health requires an understanding of their physical/chemical characteristics on the molecular scale. However, mainly due to the technical difficulties associated with the chemical diversity of environmental samples, these contaminants have never been characterized adequately. In this study, we identify the chemical form of plutonium (Pu), one of the most problematic radionuclides dispersed, in the local soils collected from one of the former weapons test sites, Maralinga. We herein reveal the first direct spectroscopic evidence that the Pu legacy exists as particulates of fine Pu oxyhydroxide compounds, a very concentrated and low-soluble form of Pu, which will serve as ongoing radioactive sources far into the future. We also verify that the Pu in the particles originated in the so-called “Minor trials” that involved the dispersal of weapon components by highly explosive chemicals, not in the nuclear explosion tests called “Major trials”. The obtained results help us to understand the chemical transformation of the original Pu materials dispersed in the semi-arid environment more than fifty years ago. These findings further highlight the importance of the comprehensive physical/chemical characterization of Pu contaminants for reliable environmental- and radiotoxicological assessment, which is significantly influenced by the original physical/chemical form of the contaminant.