Study and dispersion of radionuclides and heavy metals in coastal areas of Greece. characterized by active and past mining activities

Abstract

In this PhD work the utilization of the NORM - metal association and the application of a radiological model (ERICA) to estimate radionuclide and metal dispersion in the marine sediment, was performed. Thus, the affected area due to the anthropogenic activities was determined. Except for the spatial investigation, the marine area was also studied in a temporal aspect. The combination of the estimated sedimentation rates with the mass flux determination, lead to a well-determined time scale. Therefore, the acquired data was verified by historical records of the area. To conclude, in this work a methodology has been established to study natural radioactivity (NORM) near metal mining areas, to assess the mining activities in the area and to verify their impact on coastal areas, using chronological records. The established methodology was tested in two cases: an ongoing mining area (Stratoni, Ierissos Gulf) and an abandoned one (Oxygono Bay, Lavrio). The first has been for the last decades, a subject of investigation concerning environmental contamination due to the mining activities and waste deposits including mine tailings, flotation tailings, metallurgical slags, waste rock and pyrite concentrate stockpiles. The latter was influenced by the intensive mining and metallurgical activities over the past 100 years, which resulted in the production of huge volumes of wastes (e.g. slags, tailings) and their deposition in piles around Lavrio area, near the coastline or dumped into the sea. For this reason surface seabed sediments, water samples and sediment cores were collected from the marine environment in order to investigate spatially and temporally the impact of the mining activities. A method for assessing the distribution of contamination due to the enrichment of metals and radionuclides in the sediment was introduced. In the spatial study surface sediments were collected for the determination of natural radioactivity, major elements and trace metals. Their measurements were held in the laboratory by means of gamma-ray spectrometry and X-ray spectroscopy, while the results were combined with in situ gamma-ray measurements in the seawater, using the NaI system KATERINA. The trace metals concentrations were used for the assessment of enrichment in the sediments. The radioactivity concentrations were utilized for the enhanced NORM study and the estimation of the sediment-water coefficient Kd, useful for the dose rate assessment in the biota incorporated in the ERICA Assessment Tool. Possible correlations between trace metals, radionuclides and other parameters such as granulometry and mineralogy, were also investigated using a standard statistical software package (SPSS). To complete the spatial investigation, the dispersion of natural radionuclides (226Ra, 235U) was estimated using a simplified generic model incorporated in ERICA and the affected area due to mining was determined. The temporal study was applied in the sediment cores and included not only the statistical analysis and enrichment factor estimation, but also the radiochronology of the core and the excess mass fluxes estimations. The radiochronology was based on natural (210Pb) and artificial (137Cs) radionuclides, while the obtained trace metal profiles were verified by historical data. The estimated sedimentation rate (radiochronology), was utilized in the mass flux determination, which describes the surficial mass deposition per year and supported the unfolding of historical records included in the trace metal and radionuclide profiles. Therefore, the 100-year impact due to the anthropogenic activities was assessed.