An analysis of naturally occurring radionuclides and 137Cs in the soils of urban areas using gamma-ray spectrometry

This study of environmental radioactivity was carried out in the soils of an urban area. Naturally occurring gamma-emitting radionuclides and man-made Cs-137 were found in the soil profiles collected from four parks in the central Belgrade city area and the soil layer was examined every 10 cm and to a depth of 50 cm. Radioisotope activity concentrations (Bq kg(-1)) in the samples of urban soil using the gamma-ray spectrometry method were in the range of 14-46 for U-238, 33-50 for Ra-226, 29-63 for Pb-210, 1.2-3.4 for U-235, 28-50 for Th-232, 424-576 for K-40 and 0.7-35.8 for Cs-137. Some of the basic physicochemical soil properties (pH, organic matter content, calcium-carbonate content, particle size distribution) were determined to investigate the impact on the vertical distribution of radionuclides. The results of this investigation showed that variations of activity concentration ratios of radionuclides that belong to the same (U-238/Ra-226) or different radioactive series (Th-232/Ra-226; U-235/U-238), including Pb-210/Cs-137 ratios could well be explained by the properties of the soil. Alkaline pH reaction, the accumulation of organic matter in the uppermost and of carbonates in the deepest layers of urban soil had an effect on U-238/Ra-226, and Pb-210/Cs-137 activity concentration ratio values, while Th-232/Ra-226 and partially U-235/U-238 ratios were associated with the particle sizes vertical distribution. A study of radionuclides in the samples of leaves of two deciduous tree species common for these parks was also conducted and Pb-210 and K-40 were found concentrated in leaves rather than other investigated radionuclides.