Iodine-129, Iodine-127 and Caesium-137 in the environment: soils from Germany and Chile

Soil profiles from Bavaria in southern Germany and from Chile were analysed for 129I by accelerator mass spectrometry (AMS), for 127I by inductively coupled plasma mass spectrometry (ICP-MS), and for 137Cs by gamma-spectrometry. The mean deposition density of 137Cs in soils from Bavaria was (41×1.5±1)kBqm−2 (geometric mean and geometric standard deviation), originating mostly from the Chernobyl fall-out. The deposition density of 129I in these soils was (109×1.5±1)mBqm−2. The dominant sources of 129I in Bavaria are, however, the reprocessing plants La Hague and Sellafield and not the Chernobyl fall-out. The 129I/127I isotopic ratios of the Bavarian soils were between 10−7 and 10−10, i.e. 102–105 times higher than the ratios observed for the samples from Chile. The 129I integral deposition densities in Chile, Easter Island and Antarctica were between 0.3mBqm−2 and 2mBqm−2. In these soils, the observed 129I/127I ratios were about 10−12. The soils from Chile allow the determination of the 129I fall-out from the atmospheric nuclear weapons explosions undisturbed from contaminations due to releases from reprocessing plants. An upper limit of the integral 129I deposition density of the atmospheric nuclear weapons explosions on the Southern Hemisphere (27°S) is about 1mBqm−2. Finally, the dependence of the migration behaviour of 137Cs, 127I and of 129I on the soil properties is discussed. It turns out that there is a distinctly different behaviour of 127I, 129I, and 137Cs in the soils exhibiting different sorption mechanisms for old and recent iodine as well as for 137Cs. ► I-129 from European reprocessing plants drastically changed its natural abundances. ► We report here inventories of the Cs-137 and I-129 in Bavaria and Chile. ► The dominant sources of I-129 in Bavaria are the European reprocessing plants. ► The dominant sources of I-129 in Chile are the atmospheric nuclear test. ► I-129 and I-127 demonstrates the complex migration in the soil profiles.