Vertical distributions of 137Cs, 40K, 232Th and 226Ra in soil samples from Istanbul and its environs, Turkey

Determining the distribution of natural and artificial radionuclides in soil profiles as well as the surface layer of the soil is necessary due to the fact that radionuclides can enter the food chain from deeper soil layers and also contaminate ground water. In the current study, the activity-depth profiles of Cs-137 were determined in soil samples from 20 sites in and around the city of Istanbul. Naturally occurring radionuclides were determined at 12 of the locations. Uncultivated soil samples were taken in six horizontal layers at each location. Activity concentrations were measured with a gamma spectrometer. The impacts of texture, organic matter and pH of the soil on the vertical distribution of the radionuclides were also studied. The average and standard deviations of Cs-137 and K-40 activity concentrations in soil at a depth of 5 cm were found to be 16.4614.71 and 450.2239.1 Bq kg(1), respectively. The activity concentrations of K-40, Th-232 and Ra-226 were distributed uniformly with regard to soil depth. The depth distribution of Cs-137 generally fitted a linear function. The study revealed that 20 y after the Chernobyl disaster of 1986, 55 of Cs-137 still remains in the upper 10 cm of soil in the Istanbul environment.