Anthropogenic 129I in the atmosphere: Overview over major sources, transport processes and deposition pattern

Wet and, to a lesser extent, dry deposition of atmospheric 129I are known to represent the dominating processes responsible for 129I in continental environmental samples that are remote from 129I sources and not directly influenced by any liquid 129I release of nuclear installations. Up to now, however, little is known about the major emitters and the related global deposition pattern of 129I. In this work an overview over major sources of 129I is given, and hitherto unknown time-dependent releases from these were estimated. Total gaseous 129I releases from the US and former Soviet reprocessing facilities Hanford, Savannah River, Mayak, Seversk and Zheleznogorsk were found to have been 0.53, 0.27, 1.05, 0.23 and 0.14 TBq, respectively. These facilities were thus identified as major airborne 129I emitters. The global deposition pattern due to the 129I released, depending on geographic latitude and longitude, and on time was studied using a box model describing the global atmospheric transport and deposition of 129I. The model predictions are compared to 129I concentrations measured by means of Accelerator Mass Spectrometry (AMS) in water samples that were collected from various lakes in Asia, Africa, America and New Zealand, and to published values. As a result, both pattern and temporal evolution of 129I deposition values measured in and calculated for different types of environmental samples are, in general, in good agreement. This supports our estimate on atmospheric 129I releases and the considered substantial transport and deposition mechanisms in our model calculations.