129I measurements in lake water for an estimate of regional 129I depositions

Estimates of 129I depositions from 129I releases of reprocessing plants are so far based on measurements of soil and rain water samples. Because 129I concentrations in these samples show a highly temporal and spatial variability, the 129I deposition values deduced from single measurements cannot be seen as representative for a larger area. Here it is proposed to use lake water as an archive for former 129I depositions, to overcome these limitations. If the limnological parameters of any lake are known, the local 129I deposition flux can be deduced which is temporally averaged over the flushing time, and spatially averaged over the catchment area of the lake. Samples were collected from various European lakes and from Lake Baikal (Russia). The 129I concentration in these samples was measured by means of accelerator mass spectrometry, and values between 0.3 and 8.1×108 at/l were obtained. Deduced 129I deposition fluxes averaged over the flushing times of the lakes range from 0.3 to 9.3×1012 at/m2 y. The 129I deposition fluence measured for Lake Baikal is attributed predominantly to releases from the former Soviet reprocessing facilities Chelyabinsk, Tomsk and Krasnoyarsk, while the 129I deposition fluxes deduced for all other lakes are attributed to releases from the European reprocessing activities at Sellafield, Marcoule and La Hague.