Snežana Dragović

Inter-comparison of dynamic models for radionuclide transfer to marine biota in a Fukushima accident scenario.

We report an inter-comparison of eight models designed to predict the radiological exposure of radionuclides in marine biota. The models were required to simulate dynamically the uptake and turnover of radionuclides by marine organisms. Model predictions of radionuclide uptake and turnover using kinetic calculations based on biological half-life (TB1/2) and/or more complex metabolic modelling approaches were used to predict activity concentrations and, consequently, dose rates of (90)Sr, (131)I and (137)Cs to fish, crustaceans, macroalgae and molluscs under circumstances where the water concentrations are changing with time. For comparison, the ERICA Tool, a model commonly used in environmental assessment, and which uses equilibrium concentration ratios, was also used. As input to the models we used hydrodynamic forecasts of water and sediment activity concentrations using a simulated scenario reflecting the Fukushima accident releases. Although model variability is important, the intercomparison gives logical results, in that the dynamic models predict consistently a pattern of delayed rise of activity concentration in biota and slow decline instead of the instantaneous equilibrium with the activity concentration in seawater predicted by the ERICA Tool. The differences between ERICA and the dynamic models increase the shorter the TB1/2 becomes; however, there is significant variability between models, underpinned by parameter and methodological differences between them. The need to validate the dynamic models used in this intercomparison has been highlighted, particularly in regards to optimisation of the model biokinetic parameters.

Quantification of transfer of 238U, 226Ra, 232Th, 40K and 137Cs in mosses of a semi-natural ecosystem

There is a lack of appropriate data on transfer of some radionuclides on many terrestrial biota groups. To expand the available data concentration ratios of (238)U, (226)Ra, (232)Th, (40)K and (137)Cs in mosses are presented in this paper. The relationship between concentration ratios of radionuclides and physicochemical characteristics of the underlying soil was also investigated. The data on concentration ratios obtained here will provide a useful addition to the currently used database of transfer parameters, particularly for natural radionuclides.

Assessment of terrestrial gamma exposure to the population of Belgrade (Serbia)

The activity concentrations of (226)Ra, (232)Th and (40)K in 178 samples from 52 locations of the territory of Belgrade, the capital of Serbia, were determined by gamma-ray spectrometry. Based on the results obtained, the values of absorbed gamma dose rate at 1 m above the ground, radium equivalent activity, external hazard index, annual effective dose, annual gonadal dose and excess lifetime cancer risk were calculated. The results of the present study were compared with values reported worldwide and also with internationally recommended values. The total absorbed dose rate varied between 24.7 and 89.6 nGy h(-1) with a mean of 60.5 nGy h(-1), which is close to the world average value. Since all estimated radiological impact assessment factors were lower than the recommended values there seems to be no radiological health hazard for the population living in the investigated area.

Transfer of radionuclides to ants, mosses and lichens in semi-natural ecosystems

There is a scarcity of data on transfer of both natural and anthropogenic radionuclides to detritivorous invertebrates for use in the assessment of radiation exposure. Although mosses and lichens have been extensively used in biomonitoring programs, the data on transfer of radionuclides to these species are limited, particularly for natural radionuclides. To enhance the available data, activity concentrations of 137Cs, 226Ra and 228Ra were measured in ants, mosses and lichens and corresponding undisturbed soil collected from semi-natural ecosystems in Serbia and Montenegro and biota/soil concentration ratios (CR) calculated. Since the majority of internal dose to biota is expected to come from 40K, the activity concentrations of this radionuclide were also determined. The mean CR values for 137Cs, 226Ra and 228Ra in ants analyzed in this study were found to be 0.02, 0.06 and 0.02, respectively. The mean CR values of radionuclides in mosses were found to be 2.84 for 137Cs, 0.19 for 226Ra and 0.16 for 228Ra, while those in lichens were found to be 1.08 for 137Cs, 0.15 for 226Ra and 0.13 for 228Ra. The CR values obtained in this study were compared with default CR values used in the ERICA Tool database and also with those reported in other studies.

Using 137Cs measurements to estimate soil erosion rates in the Pčinja and South Morava River Basins, southeastern Serbia

The need for reliable assessments of soil erosion rates in Serbia has directed attention to the potential for using (137)Cs measurements to derive estimates of soil redistribution rates. Since, to date, this approach has not been applied in southeastern Serbia, a reconnaissance study was undertaken to confirm its viability. The need to take account of the occurrence of substantial Chernobyl fallout was seen as a potential problem. Samples for (137)Cs measurement were collected from a zone of uncultivated soils in the watersheds of Pčinja and South Morava Rivers, an area with known high soil erosion rates. Two theoretical conversion models, the profile distribution (PD) model and diffusion and migration (D&M) model were used to derive estimates of soil erosion and deposition rates from the (137)Cs measurements. The estimates of soil redistribution rates derived by using the PD and D&M models were found to differ substantially and this difference was ascribed to the assumptions of the simpler PD model that cause it to overestimate rates of soil loss. The results provided by the D&M model were judged to more reliable.

The Influence of Edaphic Factors on Spatial and Vertical Distribution of Radionuclides in Soil

This chapter summarises the edaphic factors affecting radionuclide spatial and vertical distribution in different soil types, with special emphasis on typical soil types in Serbia. The correlations between radionuclide and stable element content in soil and soil characteristics (particle size fractions, pH, carbonate content, organic matter content, cation exchange capacity, saturated hydraulic conductivity, specific electrical conductivity) are presented. These results provide insight into the main factors that affect radionuclide migration in the soil, which contributes to knowledge about radionuclide behaviour in the environment and factors governing their mobility within terrestrial ecosystems.

Natural radionuclides in cigarette tobacco from Serbian market and effective dose estimate from smoke inhalation

The activity concentrations of natural radionuclides ((40)K, (210)Pb, (210)Po, (226)Ra and (228)Ra) in 17 most frequently used cigarette brands in Serbia and corresponding effective doses due to smoke inhalation are presented. The mean annual effective doses for (210)Pb and (210)Po were estimated to be 47.3 and 724 µSv y(-1) for (210)Pb and (210)Po, respectively. Serbia currently has the highest smoking rate in the world. The results of this study indicate the high contribution of the annual effective dose due to smoke inhalation to the total inhalation dose from natural radionuclides. The more effective implementation of actions for reducing smoking prevalence in Serbia is highly needed.

Review of Remediation Approaches Implemented in Radioactively Contaminated Areas

The chapter aims to summarize different remediation approaches of radionuclide pollutants in water and soil media carried out after decommissioning of nuclear installations worldwide. The attention was focused on different methods of remediation, e.g. natural attenuation, bioremediation, excavating and removing contaminated soil and in situ treatments. The results of radiological assessments of the influence of nuclear cycle facilities in the environment using different modelling approach of the radionuclides transport through the environmental medium are adopted as a useful tool in decision making process applied in remediation of contaminated areas. The current trend in development strategy to support the environmental decision systems for optimization of remediation actions is to use databases on environmental and managerial parameters and radioecological models for the prediction of the effectiveness of remediation measures.

Neural networks in analysing 137Cs behaviour in the air in the Belgrade area

The application of the principal component analysis and artificial neural network method in forecasting 137Cs behaviour in the air as the function of meteorological parameters is presented. The model was optimized and tested using 137Cs specific activities obtained by standard gamma-ray spectrometric analysis of air samples collected in Belgrade (Serbia) during 2009-2011 and meteorological data for the same period. Low correlation (r = 0.20) between experimental values of 137Cs specific activities and those predicted by artificial neural network was obtained. This suggests that artificial neural network in the case of prediction of 137Cs specific activity, using temperature, insolation, and global Sun warming does not perform well, which can be explained by the relative independence of 137Cs specific activity of particular meteorological parameters and not by the ineffectiveness of artificial neural network in relating these parameters in general. [Projekat Ministarstva nauke Republike Srbije, br. TR34034]