Speciation: Radionuclides

Abstract

AbstractTo assess the environmental impact of radioactive contamination of different ecosystems, information on source terms, mobility, biological uptake, and associated effects is needed. However, naturally occurring and artificially produced radionuclides can be present in different physicochemical forms (ions, colloids, nanoparticles, pseudocolloids, particles) influencing the mobility and biological uptake. Following severe nuclear events associated with the nuclear weapon or fuel cycles, a major fraction of refractory radionuclides will be present as radioactive particles; radionuclides are also present as colloids or low molecular mass (LMM) ionic species in effluents from nuclear installations. Thus, the distribution of radionuclide species depends on the source and release scenarios. LMM radionuclide species are believed to be mobile and potentially bioavailable, while high molecular mass (HMM) species such as nanoparticles, colloids, polymers, and pseudocolloids are mobile in water. Radioactive particles are considered biologically inert, but can be retained in filtering organisms as well as in soils and sediments. If mobile species are present, ecosystem transfer is relatively fast, whereas the ecosystem transfer is delayed if particles are present. Owing to time‐dependent transformation processes such as interactions of mobile and reactive radionuclide species with components in soils and sediments or particle weathering and subsequent remobilization of associated radionuclide species, the original distribution of radionuclides deposited in ecosystems will change over time. Therefore, information on radionuclide species released and deposited, as well as on time‐dependent transformation processes influencing the distribution of radionuclide species, is essential for the assessment of the environmental impact and risk associated with radionuclide contamination. This article summarizes available speciation techniques that should be utilized within radioecology, including fractionation and solid‐state speciation, to characterize radionuclide species in waters, soils, and sediments.