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

Abstract

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.