Distribution and temporal variability of uranium and toxic metal(loid)s in snow and rainwater from an oil industry and urban area in Thessaloniki-Greece.

The concentrations of uranium and nine elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in snow and rainwater samples were determined. Samples were collected in Thessaloniki-northern Greece in three sites, one in the industrial area close to an oil production power plant and two in the centre of the city. Snow samples were collected during January-February 2019 and 2021 whereas in the case of rainwater, a two-year survey has been performed during 2019 and 2020. The activity concentrations of the uranium radioisotopes were measured by alpha spectrometry whereas the metal(loid)s concentrations were determined by inductively coupled plasma mass spectroscopy (ICP-MS). The elevated concentrations of uranium (U) and the deviation of the isotopic ratio of U-234/U-238 from the equilibrium value indicated intensive dissolution of uranium. The results were analyzed using statistical analysis (Shapiro-Wilk, Friedman and Kruskal-Wallis tests). The obtained data and the calculated enrichment factors (Efs) denote variation of the concentration values between industrial and urban area and different elemental distribution influenced from anthropogenic contributions, meteorological conditions and the COVID-19 pandemic.

Uranium and Thorium water decontamination via novel coated Cu-based nanoparticles; the role of chemistry and environmental implications.

The removal of radioactive contaminants from aquifers is a matter of great concern. In this paper, coated copper-based nanoparticles (Cu-based NPs) were investigated as sorbent materials to remove uranium and thorium from low-level wastes, and especially from water, considering the influences of temperature, time, concentration, and pH. Cu-based NPs were derived through a hydrothermal synthesis from copper nitrate degradation in the presence of the bifunctional with COOH-terminated PEG, TEG as well as PEG 8000. The characterization was undertaken using XRD, TEM, TG/DTG, FTIR, and SEM-EDS. Isotherm models such as Langmuir and Freundlich were applied, while kinetic data were successfully reproduced by the pseudo-second-order equation and thermodynamic parameters were calculated. To investigate the removal mechanisms, UV-fluorescence and X-ray photoelectron spectroscopy were used. In the case of uranium, the predominant mechanism includes the formation of surface complexes, followed by extensive reduction (65%) of U(VI) to less soluble U(IV) while in the case of thorium, surface precipitation dominates. Copper nanoparticles exhibited significant U(VI) uptake capacity resulting in a decrease of the U-concentration below the acceptable limit of 30 µg/L and can be successfully applied in water treatment technology.

Cesium and barium removal from aqueous solutions in the presence of humic acid and competing cations by a Greek bentonite from Kimolos Island.

The Cs- and Ba-sorption, onto bentonite from Kimolos island (Cyclades, Greece) was investigated in aqueous solutions in the presence of Na+, Ca2+ and humic acid. Batch experiments were performed using as tracers 137Cs and 133Ba and γ-ray spectroscopy. The sorption significantly depended on initial concentration, ionic strength and temperature of the solutions. The sorption isotherms were satisfactorily reproduced by the Langmuir and Freundlich equations. The kinetic experiments at 293, 308 and 323 K and the calculation of the thermodynamic parameters (ΔH, ΔS° and ΔG°) indicated that Cs- and Ba-sorption was spontaneous and endothermic process. The sorbent was characterized before and after the sorption experiments using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM-EDS). It was demonstrated that the Kimolos bentonite is a good sorbent for cesium and barium from highly contaminated solutions and its sorption capacity reduced in presence of humic acid and competing cations.

Seasonal variations of natural radionuclides, minor and trace elements in lake sediments and water in a lignite mining area of North-Western Greece.

The radiological and chemical pollution of a cluster of four lakes in a lignite mining area of North-Western Greece was investigated using a variety of analytical techniques. Alpha spectrometry was applied to measure the activity concentrations of the uranium radioisotopes (U-234, U-235, and U-238) in waters. The mass activities of U-238, Th-232, and K-40 in sediments were measured by high-resolution gamma spectrometry. Furthermore, the determination of the minor and trace elements was carried out by instrumental neutron activation analysis (INAA) in both water and sediments samples, respectively. Pollution levels were also evaluated by calculating enrichment factors (EFs), contamination factors (CFs) and pollution load index (PLI). The data were discussed taking into account several parameters such as the distance from the pollution source, temperature, and location and showed that the environmental impact in this region could not be considered as negligible. The deviation of the isotopic ratio of U-234/U-238 from the equilibrium value indicated waters with intensive dissolution of uranium. The activity values in both waters and sediments found to be low in cool periods and increased in warm periods. Moreover, the concentrations of the elements U, Zn, and Fe were raised in water samples indicating possible pollution as well as the CFs and PLI denoted accumulation in the sediments and moderate to severe contamination for Zn and Cr in some cases.

Retention of barium and europium radionuclides from aqueous solutions on ash-based sorbents by application of radiochemical techniques.

New materials were synthesized for application in sorption of radionuclides from aqueous solutions. The elaboration was performed by conversion of power plant ash using the hydrothermal method under optimum experimental conditions. Sodalite, Na-Y, and analcime were formed from ash precursor during the treatment, exhibiting thermal stability as revealed by the characterization by X-ray diffraction (XRD) and thermogravimetric differential thermal analysis (TG-DTA). The Brunauer-Emmett-Teller (BET) surface area and pore volume were determined and they presented higher values than plant ash. The ability of the new products to retain Ba and Eu radionuclides was studied in aqueous solutions using (133)Ba and (152)Eu as tracers and γ-ray spectroscopy under batch experiments. The experimental data were modeled by the Langmuir and Freundlich equations, whereas sorption kinetics measurements were performed at 293, 308, and 323K and thermodynamic parameters were calculated. The release of the sorbed ions into the environment was also tested by leaching experiments. The results of these tests indicated that the synthesized materials are very efficient in removing the aforementioned metals from aqueous solutions and can be considered as potential low-cost sorbents in nuclear waste management.

Concentration of heavy metals and trace elements in soils, waters and vegetables and assessment of health risk in the vicinity of a lignite-fired power plant.

The pollution of agricultural soils, waters and products in the regions of lignite mines and fired power plants is of great importance. The concentration of As, Βa, Co, Cr, Sr, Sc, Th, U, Zn in soils and waters in the vicinity of a lignite-fired power plant in Northern Greece was determined using Instrumental Neutron Activation Analysis. The determination frequency was every three months during a period of one year in order to evaluate the seasonal impact of the pollution to the environment. Measurements were performed in three locations around the lignite mine as well as in one reference location at a certain distance from the mine. The results, which exhibited a slight seasonal variation, were compared, where possible, with literature values from other countries. The obtained data in most of the cases did not exceed the normal levels and indicated that the investigated area was only slightly contaminated. The concentration of heavy and trace metals was also measured in three common garden crops (tomato, cucumber and parsley) grown in this area. The calculated transfer factors (TF) from soil to vegetables and health risk quotients (HQ) do not denote a health risk.

The uranium isotopes in the characterisation of groundwater in the Thermi-Vasilika region, northern Greece.

The activity concentrations of (238)U and (234)U have been determined in groundwater samples in the Thermi-Vasilika region, northern Greece. The analysis was performed by alpha spectrometry after pre-concentration and separation of uranium by cation exchange and finally its electrodeposition on stainless steel discs. The obtained isotopic ratio (234)U/(238)U varies between 0.95 and 3.50 and is correlated with the different aquifer types and water flow paths in the study area. Lower values (up to 1.10) are located in the shallow porous aquifer indicating younger waters. Moderate values of the activity ratio characterise the deeper porous aquifer as well as the fissured rock aquifer (1.5-2.05). The geothermal spring illustrates the highest activity ratio (3.5) due to older water.