High-resolution records of cesium, plutonium, americium, and uranium isotopes in sediment cores from Swiss lakes.

The Aare river system in Switzerland, with two nuclear power plants on the banks of the river, and its intermediate lakes and reservoirs, provides a unique opportunity to analyze the contribution of different sources to the radioactive contamination. Sediment cores were collected from two lakes and a reservoir, all connected by the river Aare. In order to study the influence of the Chernobyl accident, one sediment core was collected from a lake in the southern part of Switzerland. The sediment cores were sliced and analyzed with gamma ray spectrometry. Plutonium, americium, and uranium were extracted radiochemically, and their concentrations were measured with a sector field ICP-MS. The uranium isotope ratios were further measured with a multi collector ICP-MS. The maximum 137Cs activity from the Chernobyl accident and the Pu and 137Cs activities associated to the 1963 global fallout maximum were well identified in sediments from all three lakes. High-resolution records of plutonium isotopes in the zone of the sediments corresponding to the period of maximum fallout from the atmospheric nuclear weapon testing showed distinct fingerprints, depending on the different test activities. Pu isotope ratios could be used to detect non-global fallout plutonium. The ratio 241Am/241Pu was used to determine the age of the plutonium. Despite of very low 241Pu and 241Am concentrations, the calculated plutonium production dates seemed to be reasonable for the sediment layers corresponding to the NWT tests. The calculated production date of the plutonium in the upper most 15 cm of the sediment core seemed to be younger. The reason for this could be additional non-global fallout plutonium. For the lake sediments, natural ratios for 235U/238U and enriched or depleted ratios for 234U/238U were measured, depending on the lake. A small increase of the 236U/238U ratio could be recognized for the NWT zone in all three lakes and, for Lake Lugano, a further distinct increase in the Chernobyl layer.

Time-dependency of the 137Cs contamination of wild boar from a region in Southern Germany in the years 1998 to 2008.

Following the Chernobyl accident, (137)Cs contamination levels of wild boar in some districts of Southern Germany are still exceeding thousands of Bq kg(-1). While the long term (137)Cs concentration in forest plants, mushrooms, and roe deer meat has decreased significantly, for wild boar it has remained constant during the last decade. Between 1998 and 2008, we analysed the muscle meat of 656 wild boars shot in the district ("Landkreis") Ravensburg. The (137)Cs activity concentration showed considerable variability from less than 5 up to 8266 Bq kg(-1) and it followed a seasonal pattern, which is attributed to changes in dietary habits, fodder availability, meteorological conditions and specific behaviour of (137)Cs in wild boar organism. T(ag) values for wild boars from the district Ravensburg varied from 0.008 to 0.062 m(2)kg(-1) during 2000-2008.

Migration of 137Cs in tributaries, lake water and sediment of Lago Maggiore (Italy, Switzerland) - analysis and comparison with Lago di Lugano and other lakes.

This paper describes the behaviour of 137Cs in Lago Maggiore and other pre-alpine lakes as a consequence of atmospheric nuclear weapons testing fallout and the fallout from the nuclear accident in Chernobyl. It presents data on the 137Cs distribution in tributaries, lake water, bottom sediments and reveals the role of (137)Cs as a marker of the sedimentation processes. The run-off of 137Cs from the watershed to the lake is described with a simple compartment model. Measurements of the activity concentration of (137)Cs in sediments are compared with the output of a model (diffusion-convection type) which describes the input of 137Cs into and its vertical distribution within the sediment. Varying sedimentation rates (0.05-0.90g(cm2y)(-1)) in Lago Maggiore are compared with data of other authors. Sedimentation rates and total distribution coefficients (of about 10(5) Lkg(-1)) in Lago Maggiore are discussed and compared with those of Lago di Lugano, Lake Constance, and Lake Vorsee.

Modeling 137Cs migration processes in lake sediments.

Lake sediments can be considered as the "diary" of the lake: new layers are continuously deposited on top of the sediments. The migration behavior of radionuclides, particularly of (137)Cs, can be analyzed by modeling the input into and the vertical distribution within the sediment. For this purpose, a model consisting of sedimentation-diffusion equations was developed. Solved with a finite element method, this model can cover the time period from the nuclear weapons testing to the present. It takes into account fixation and redissolution, compaction of sediments, and the influence of competing ions on the retarded diffusion within the sediments. The outcome of the model is compared to water and sediment measurements from Lago Maggiore. The results of an optimization process can produce the sedimentation rate and (137)Cs distribution coefficients which determine the uptake of activity into the sediment and also the retarded diffusion within the sediment.