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Spatial distribution of natural and artificial radionuclides in soils in Greece

Terzidis Konstantinos

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Summary

In the present thesis the behavior of natural and artificial radionuclides in Greek soils is examined. The aim of the thesis is to accomplish the spatial distribution of the radionuclides in the examined areas and simultaneously evaluate the environmental danger which occurs from these radionuclides, by calculating the appropriate environmental indices.The areas from which we had soil samples are Lesvos, Chios and Thessaly. More precisely, we had 18 soil samples from Lesvos, 8 soil samples from Chios and 19 soil samples from Thessaly.The radionuclides examined for this thesis are Radium (226Ra, 228Ra), Uranium (238U), Thorium (228Th, 232Th), Potassium (40K) and Caesium(137Cs). From the aforementioned radionuclides Radium, Uranium, Thorium and Potassium belong to natural radionuclides, whereas Caesium belongs to artificial. Furthermore, the correlation between these radionuclides is studied by applying PCA and calculating the Pearson’s correlation coefficients.In order to carry out the spatial distribution of the radionuclides in the studied areas, the method of Inverse Distance Weighting (IDW) was used. Namely, the resulting spatial distribution maps were based on the assumption that the characteristics of the samples closer to each other are more similar than the characteristics of those further apart.Regarding the assessment of the environmental danger resulting from the examined radionuclides, the necessary environmental indices were used. In more detail, the Geo-accumulation Index (IGEO), the Enrichment Factor (EF) and the Pollution Index (PI) were calculated for the determination of the pollution of the soils from each radionuclide separately. In Lesvos, increased Enrichment Factor and Pollution Index values were observed whereas in Chios and Thessaly these indices presented small values. Generally, little pollution is found by radionuclides in the examined areas, with medium pollution levels in Lesvos due to the effect of specific local geological circumstances. Moreover, several safety radiation parameters were found in order to assess the danger on human health by the radionuclides. Specifically, these parameters are the External Hazard Index (Hex), the Radium equivalent activity (Raeq), the dose (D) and the effective dose (DE). Lesvos, presented higher values for the above parameters compared to Chios and Thessaly. It is important to highlight that in Argennos and in Arisvi Hex and Raeq values were found to be higher than the acceptable limits. Finally, there was a separate calculation of the Caesium dose (DCs) and the effective dose of Caesium (DE(Cs)) because Caesium belongs to the artificial radionuclides and its danger assessment is of big interest. Lesvos and Thessaly, presented similar values when it comes to Caesium parameters, whilst in Chios those values were smaller. In conclusion, the danger for human health in the examined areas both from natural radionuclides and Caesium is minor.

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