Characterization of 210Pb and 137Cs radionuclides in sediment from Lake Shinji, Shimane Prefecture, western Japan

The characterization and chemical behaviors of (210)Pb and (137)Cs in the surface sediment (4-7 cm depth from the bottom) from Lake Shinji, Shimane Prefecture, western Japan, are studied by grain size and phase analyses. Their activities had increasing trend in silt fractions with decreasing grain size, while those in sand fractions did with increasing grain size. The (40)K content had the general increasing trend with increasing grain size. These trends might be derived from the mineral component and the adsorption mechanism of these nuclides. By using the sequential extraction technique, most of (214)Pb, (137)Cs and (40)K were proved to be contained in silicate fraction. A part of (210)Pbex presumably existed as carbonate and iron manganese oxides for coarser grains, and as iron manganese oxides for finer grains, in addition to silicate fraction. Although (210)Pb and (137)Cs may occupy the different sites and exist in different chemical phases, the bulk contents in the samples from a variety of locations within the same lake showed a generally good correlation. This result suggests their similar depositional process within a lake in a macroscopic view, being one of the evidences for the validity of sedimentation chronology in the field.