The validation of the dynamic food chain model BURN-POSEIDON on Cs-137 and Sr-90 data of the Dnieper-Bug estuary, Ukraine

The uptake of radioceasium and radiostrontium in biota in dose assessment models is mostly estimated on the basis of Concentration Factors (CF). For accidental releases, the dynamical foodweb model BURN has been implemented in the coastal model POSEIDON (part of the Decision Support System RODOS). BURN can be applied on water bodies with different salinity levels, since in the model the uptake of radioceasium and radiostrontium in phytoplankton is governed by potassium and calcium in the water, which are calculated via the easier-to-obtain parameter salinity. Recently a dataset on radiocaesium and radiostrontium has been collected for various aquatic organisms in the Dnieper-Bug Estuary (DBE) in Ukraine, which enabled model validation with BURN. Considering the limitation of compartment models and the fact BURN is a predictive model, with fixed model parameters, the model results are within a reasonable range with the measurement data. Besides comparison with measurement data, the model calculations were also used to derive values for CF and compared with literature, which gave reasonable results for Cs-137 in fish and molluscs. For Sr-90 however, the calculated values exceeded the levels given in literature, since equilibrium between radionuclides in biota and water is not reached. Longer time periods for the radionuclide flux into the DBE, both from the Dnieper and the Black Sea are required to obtain high quality model results for the years after 1989.