The importance of physico-chemical parameters on the speciation of natural radionuclides in riverine ecosystems

External gamma radiation levels were measured in the catchment areas of the Sharavathi River and the dose rates in air were found to be in the range 26.0–61.0 nGy h−1. Soil and sediment samples of the riverine environment were analysed for natural radionuclides such as 226Ra, 232Th and 40K using a NaI(Tl) gamma spectrometer. The activity concentration of 210Pb and 210Po in soil and sediment samples was determined by radiochemical separation techniques. Evaluation of the activity concentration of radionuclides with grain size revealed an increase in the activity of 226Ra, 232Th and 40K towards fine grain size. The activity concentrations for all isotopes in all samples were not significantly correlated with pH. However, the activity of 210Po and 210Pb in sediment showed a moderate positive correlation with organic matter content and a good correlation with clay content of sediment.