Fukushima’s Forgotten Radionuclides: A Review of the Understudied Radioactive Emissions

In environmental monitoring campaigns for anthropogenic radionuclides released in the course of the Fukushima nuclear accident (2011), most focus had been on gamma-emitting radionuclides. More than 99% of the released activity was due to radionuclides of the elements Kr, Te, I, Xe, and Cs. However, little work had been done on the monitoring of radionuclides other than 131I, 132Te, 134Cs, 136Cs, and 137Cs. Radionuclides such as those of less volatile elements (e.g., 89Sr, 90Sr, 103Ru, 106Ru, plutonium), pure beta-emitters (3H, 14C, 35S), gaseous radionuclides (85Kr, 133Xe, 135Xe) or radionuclides with very long half-lives (e.g., 36Cl, 99Tc, 129I, some actinides such as 236U) have been understudied by comparison. In this review, we summarize previous monitoring work on these “orphan” radionuclides in various environmental media and outline further challenges for future monitoring campaigns. Some of the understudied radionuclides are of radiological concern, others are promising tracers for environmental, geochemical processes such as oceanic mixing. Unfortunately, the shorter-lived nuclides of radioxenon, 103Ru, 89Sr and 35S will no longer exhibit detectable activities in the environment. Activity concentrations of other radionuclides such as tritium, 14C, or 85Kr will become blurred in the significant background of previous releases (nuclear explosions and previous accidents). Isotope ratios such as 240Pu/239Pu will allow for the identification of Fukushima plutonium despite the plutonium background.