Journal of Radioanalytical and Nuclear Chemistry, Vol. 266, No. 1 (2005) 3137 02365731/USD 20.00 AkadØmiai Kiad, Budapest ' 2005 AkadØmiai Kiad, Budapest Springer, Dordrecht Migration processes of 137 Cs and 90 Sr in compartments of a lake ecosystem D. Desideri, 1 C. Grimani, 2 L. Monte 3 1 Institute of General Chemistry, Urbino University, P.zza Rinascimento 6, 61029 Urbino, Italy 2 Institute of Physics, Urbino University, Via S.Chiara 27, 61029 Urbino, Italy 3 ENEA CR, Casaccia, Via Anguillarese 301, CP 2400, 00100 Rome, Italy (Received August 11, 2004) The dispersion of radioactive substances in the environment following nuclear weapon tests in atmosphere since 1954 and accidents to nuclear plants, like that in Chernobyl in 1986, have allowed us to study the migration processes of some radionuclides in complex ecosystems such as lakes are. In the present paper the behavior of 137 Cs and 90 Sr in different compartments of the Monterosi Lake (central Italy) was assessed. The 137 Cs concentration was measured in lake water as well as sediment, stream water, aquatic plant and fish samples. 90 Sr concentration in water and sediments was also determined. A total inventory of 4206–76 Bq . m 2 and 958–79 Bq . m 2 (on 27/6/01) has been found for 137 Cs and 90 Sr, respectively. The experimental data presented here allow to calibrate theoretical models predicting the temporal trend of radionuclide concentration in similar ecosystems. Moreover, information on cesium and strontium migration processes can be extended to other pollutants having similar environmental behavior. Introduction Human produced activities can introduce pollutants in the environment causing, in some cases, high and persistent contamination levels in the ecosystems. The appropriate management of fresh water ecosystem contaminated by these pollutants requires the assessment of the costs and benefits of countermeasure and restoration strategies aimed reducing the dose burden to man. Any environmental intervention may cause, however, non-desirable effects of ecological, economic and social nature. Consequently, critical evaluations of different management strategies are necessary to determine which of these reach the optimal balance between the related benefits and costs. Such an assessment requires the development of models to predict the behavior of radionuclides in the fresh water environment, the effect of the countermeasure interventions (restoration actions) on the levels of pollution and the ecological, social and economic impacts of such interventions. These models should based on experimental data. 1,2 Radionuclide release in the environment due to nuclear weapon tests into the atmosphere and accidents to nuclear plants have permitted to study the behavior of some radionuclides in complex ecosystems. Recently, many experimental studies following the most significant nuclear accidents (including Chernobyl) have provided the opportunity for a quantitative evaluation of the most important transfer parameters of some radionuclides through various ecosystems. Consequently, the uncertainty on these parameters and, thus on the models, has become considerably lower with respect to a decade ago. Most models focus mainly on radiocesium and radiostrontium as these radionuclides * E-mail: d.desideri@uniurb.it are particular important for their long radioactive decay times and the consequent persistence in the environment. Moreover, information on cesium and strontium migration processes can be extended to other pollutants having a similar environmental behavior. As an example, some models developed for the prediction of the behavior of toxic substances in the environment are based on the assumption that radionuclides such as 137 Cs and 90 Sr show chemical (and biochemical) behaviors similar to potassium and calcium, respectively. 3 In the present paper 137 Cs and 90 Sr concentration measurements are reported in different compartments of the lacustrine ecosystem of the Monterosi lake (a small stagnant lake in the Sabatini mountains, north of Rome). 137 Cs was released into the atmosphere by nuclear weapon tests in the period od 19541978 and after the Chernobyl accident (1986). Conversely, the 90 Sr contamination in Italy was caused by nuclear weapon tests. 137 Cs and 90 Sr concentration measurements in the lake water repeated during more than one decade allow to study: (1) the two radionuclide concentration temporal trend, (2) their different reactivity with the particulate matter and (3) their migration fluxes to the sediments. Concentration measurements in sediments permit to evaluate the radionuclide concentration trend as a function of the depth and inventory. Finally, concentration measurements in aquatic plants and fishes allow to determine the bioaccumulation factors. These last ones give precious hints about the migration processes of the above radionuclides from water, through the trophic levels, to the organisms living in it and eaten by people.