Radioactive particles from a range of past nuclear events: Challenges posed by highly varied structure and composition

While they have appeared only recently in earth's history, radioactive particles from anthropogenic sources are widespread in global environments and present radiological harm potentials to living organisms. Exposure potentials vary greatly, however few studies examine a wide range of source and particle types. Here we compare a varied set of particles from past nuclear fission and non -fission sources in Australia of highly diverse magnitudes, release modes, and environments. The radiochemistry and microscopy methods revealed that numerous radioactive particles persist in soils 60+ years after their release events. Particles can be distinguished by their Ca/Fe and Si/Fe elemental ratios, which in this study range over orders of magnitude and reflect the materials available during their individual formation events. The particles with Si-and Ca-dominant compositions persisted in corrosive environments (e.g., marine). Internal fracturing is more prevalent than previously reported, and fracturing is greater in Ca-rich vs. Si-dominated matrices. The fractures often form connective pathways from the interior to exterior surfaces, increasing the potential to leach radionuclides into a host organism or the environment. The particles from nuclear testing have dominant Pu239+240 activity concentrations, relative to Sr-90 and Cs-137, which increases long-term radiological hazard from alpha emissions if inhaled or ingested, and contrasts with particles from nuclear power accidents (e.g., Fukushima). Additional physical/chemical/radiological measurements are needed to fully understand longterm fate and hazard potentials.

Automated summary

Radioactive particles from anthropogenic sources are widespread in global environments and have the potential to cause radiological harm to living organisms. This study compares a diverse set of particles from past nuclear fission and non-fission sources in Australia, revealing that many radioactive particles persist in soils even decades after their release events. The particles can be distinguished by their elemental ratios and their compositions affect their persistence and potential to leach radionuclides into the environment or organisms.