Determination of natural radioactivity and heavy metal pollution of Kulakcayiri Lake

Natural and artificial radionuclide distribution, trace elements, and gamma dose rate values in and around the lake were detected in the present study based on the drilling core sediment samples collected from Kulakçayırı Lake located in the city of Istanbul, district of Arnavutköy at various depths (SK-1=5-5,5 m, SK-2=10-10,5 m, SK-3=15-15,5 m) using drilling method, and mineralogical and textural properties are identified using XRD analyses and SEM images. Moreover, ages of the sediments in the region are detected and calculated the sedimentation rates using radiocarbon dating method. Samples are counted using HPGe detector in order to calculate the radioactivity concentration. Based on the analysis results, while the K-40 concentrations of the samples are calculated as 325±18 Bq/kg, 353±19 Bq/kg, and 367±19 Bq/kg respectively, the Th-232 concentrations are calculated as 38±6 Bq/kg, 43±6 Bq/kg, and 42±6 Bq/kg. Besides, while the Ra-226 concentrations are calculated as 29±5 Bq/kg, 26±5 Bq/kg, and 26±5 Bq/kg respectively, the Cs-137 concentrations of the three samples are calculated as ≤MDA, and found out to exist at extremely low concentrations. Mean activities of the samples are calculated, and it is observed that the mean value is 348±186 for K-40 isotope, 41±6,3 for Th-232 isotope, and 27±5,1 for Ra-226 isotope. Measurements are taken at twenty locations with 12 km intervals in and around the lake in order to determine the radiation released by the terrestrial radiation to the environment, and gamma dose rates were determined. Outdoor gamma dose rates in the air at 1 meter above the ground level are measured using ESP-2 (Eberline Smart Portable) scintillator. Measurements were taken at 20 locations once hourly, and the mean value of the measurements is 37,5 nGy/h. Calcium oxide (CaO), titanium oxide (TiO2), and hematite (Fe2O3) concentrations are determined with nineteen different elements using WDXRF spectrometry in trace element analyses. Elemental analysis revealed that heavy metals such as cobalt, nickel, copper, lead and chromium and radioactive elements such as uranium and thorium are detected in the sediment structures. Lead concentration is measured as elevated especially in SK-1 sample. This elevated value is caused by the sediment structure around the lake which is natural. XRD analyses of the samples are conducted using Bruker D8 Advantage, Panalytical X'Pert Powder, and Philips PW 1830 make and model equipment. Mineralogical compositions of the samples are determined in XRD analyses and the SEM images are defined using JEOL JSM-6390LAV equipment. SEM images manifested a complex structure due to the fact that the sediments are not standard materials and consist of various organic and inorganic compounds. A large number of peaks are obtained in XRD analyses corresponding to various minerals. It is seen that the detected peaks correspond to hematite (Fe2O3), quartz (SiO2), calcite (CaCO3), and corendon (Al2O3) among the minerals. AMS spectrometry is used for radiocarbon dating method. According to the sample results; while sediment precipitation in SK-1 sample occurred in 5599 years, occurred in 7596 years in SK-2, and occurred in 8060 years in SK-3. Sedimentation rates are in SK-1>SK-2>SK-3 order. Based on the obtained data, it is observed that the sedimentation rate varies at various depths. Keywords: Kulakçayırı Lake, sediment, natural radioactivity, gamma spectrometer, gamma dose rate, XRD, SEM, radiocarbon dating