Estimations of 137Cs activity concentrations using marine parameters issued from MODIS and Copernicus Marine Environment Monitoring Services (CMEMS) data in Souda Bay (Crete, Greece) for the period 2011-2019.

Cesium-137, as the main fission product, is of special interest in the marine environment because of its solubility, which results to very low sinking time. Nevertheless, the conservative form of the main percentage of 137Cs introduced in the marine environment (70%) makes 137Cs to be included in the salinity of sea water. Based on this property, in this study, we examine potential relations between 137Cs activity concentrations and marine parameters issued from Earth Observation (EO) data products in the Southern Aegean Sea, in order to investigate the possibility of 137Cs to be recorded by satellite data. In particular, measurements of physical and biological marine parameters issued from the Copernicus Marine Environment Monitoring Service (CMEMS) database and MODIS ocean products are retrieved for the dates of 137Cs field measurements. Single and multiple regression analyses are performed between the marine parameters and 137Cs activity concentration measurements for three distinctive time periods (total, cold, and warm period). The best results are obtained from multiple regressions, one for each time period (r2 > 0.70). The models show that during cold period, 137Cs activity concentrations are highly correlated to both chlorophyll and nutrients (phosphates) while during warm and the total period, they seem to be mainly correlated to the photosynthetic available incident solar radiation on the sea surface. For each period, we propose a multiparameter model linear in its parameters. Although the results of this study must be considered preliminary due to the limited size of the datasets, for the first time, we show that estimations of 137Cs activity concentrations from EO measurements and CMEMS environmental models are feasible, and they can be used as a marine radiological assessment tool for a closed Mediterranean bay such as Souda Bay in Greece.

Determination and mapping of the spatial distribution of cesium-137 in the terrestrial environment of Greece, over a period of 28 years (1998 to 2015).

In this study, we are applying the GIS techniques in order to record the data that have been collected for cesium-137, over the for the period 1998 to 2015, for the terrestrial environment in Greece. Following the Chernobyl Nuclear Power Plant (CNPP) accident in 1986, extended fieldwork was conducted for the determination of cesium-137 concentrations in the terrestrial environment. In 2011, in the light of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, new campaigns were organized in order to assess the variation in cesium-137 activity concentrations. The measured data, combined with data taken from the databases of the Environmental Radioactivity Laboratory (NCSR'Demokritos', in Athens, Greece), as well as, from the European Atlas of Cesium Deposition on Europe, are being used for the spatial distribution analysis of cesium-137 in the country. Furthermore, are used for the temporal analysis of this radionuclide in a long-term basis. Moreover, we are using the ERICA Assessment Tool for the calculation of the dose rate that the studied organisms (plants of Poaceae spp. and mammals of Bovidae spp.) receive due to the exposure to cesium-137. All gathered information provides us with thematic maps, designed through the GIS techniques, that allow for an appropriate representation of cesium-137 presence in the country nowadays. This study provides an insightful view of the behavior of this anthropogenic radionuclide that is useful for future research in order to elucidate its behavior in long-term periods. The knowledge of the environmental fate of radionuclides is important because it contributes to the projection of long-term risks resulting from radionuclide releases, as well as, for the selection of cost-effective remediation strategies. Furthermore, it provides the opportunity to conduct a comprehensive risk assessment in the region, as the studied organisms were exposed to low-level ionizing radiation. But, as it was shown, on the level of ecosystem, no significant impact was estimated. However, regarding the future objectives, further consideration of the exposure levels should be considered while taking also into account the exposure to natural and background radiation and the exposure to spontaneous emission of anthropogenic radionuclides, especially if we want to consider the eventual effects of protracted low-level ionising radiation on the various levels of life's organization.