Natural and man-made radionuclides in sediments of an inlet in Rio de Janeiro State, Brazil

The distribution of natural radionuclides Ra-226, Ra-228, K-40 and man-made radionuclides (Mn-54, Co-60 and Cs-137) in the surface sediments of an inlet of Ribeira Bay were investigated. Sediment samples were collected and analyzed for radionuclides, organic matter, carbonate, sulfate, cationic exchange capacity and grain size composition. The natural radionuclide concentrations ranged from 4.4 to 45, from 10 to 93, from 66 to 1347 Bq. kg(-1) dry weight for Ra-226, Ra-228 and K-40, respectively. Natural radionuclide concentrations tend to be higher in the silt fraction, which determines their pattern distributions. Only one sample presented measurable concentration for Cs-137, while Mn-54 was detected in two samples and Co-60 in four sediment samples. Man-made radionuclides present a maximum value of dose external four times lower than the normal background and the potential risk due to the presence of man-made radionuclides in sediments is lower than the risk provided by the natural radionuclides. (C) 2016 Elsevier Ltd. All rights reserved.