Estimate of European ¹²⁹I Releases Supported by ¹²⁹I Analysis in an Alpine Ice Core

¹²⁹I in the European environment originates predominantly from the industrial nuclear fuel reprocessing plants Sellafield (Great Britain), Marcoule, and La Hague (both France). While reliable data on ¹²⁹I releases from La Hague exist for the whole period of operation, less is known about the contributions from Sellafield and Marcoule. For those periods where no data are available, i.e., for the first 16 years of the Sellafield operation and for the first 3 decades of the Marcoule operation, we estimated releases into the atmosphere of 118 GBq and 825 GBq, respectively. Hence, Marcoule was the major European source of airborne ¹²⁹I, contributing about 45% to the total airborne ¹²⁹I releases from all the European reprocessing facilities, until it was decommissioned in 1997. The estimated total emissions were compared with ¹²⁹I deposition fluxes for the time period 1970−2002, obtained from the analysis of an ice core from Fiescherhorn glacier, Swiss Alps (46°33'N, 08°04'E; 3900 m asl). The temporal evolution of the ¹²⁹I deposition agrees well with the total ¹²⁹I releases into the atmosphere from the European reprocessing facilities and from atmospheric nuclear weapons tests, supporting our estimated release rates. However, the ¹²⁹I concentrations and deposition fluxes at Fiescherhorn glacier were a factor of 6 lower than values obtained from the analysis of rainwater collected near Zurich (408 m asl) in Switzerland in the years 1994−97. This suggests a strong vertical concentration gradient of ¹²⁹I, typical for water-soluble atmospheric trace species which are removed from the atmosphere in the course of days by precipitation scavenging, and must be taken into account if glaciers are used as an archive for a retrospective quantification of ¹²⁹I deposition fluxes. In addition, the temporal evolution of the contribution of ¹²⁹I re-emitted from the ocean's surface for the ¹²⁹I inventory in the atmosphere was quantified for the first time. Although the annual amount of ¹²⁹I released this way was very low until the early 1990s, it is similar to the airborne ¹²⁹I releases from Sellafield and La Hague in the present time.