Plutonium in Soils from Northeast China and Its Potential Application for Evaluation of Soil Erosion

Surface and soil core samples from northeast China were analyzed for Pu isotopes. The measured Pu-240/Pu-239 atomic ratios and Pu239 + 240/Cs-137 activity ratios revealed that the global fallout is the dominant source of Pu and Cs-137 at these sites. Migration behavior of Pu varying with land type and human activities resulted in different distribution of Pu in surface soils. A sub-surface maximum followed by exponential decline of Pu239 + 240 concentrations was observed in an undisturbed soil core, with a total Pu239 + 240 inventory of 86.9 Bq/m(2) and more than 85% accumulated in 0 similar to 20 cm layers. While only half inventory of Pu was obtained in another soil core and no sub-surface maximum value occurred. Erosion of topsoil in the site should be the most possible reason for the significantly lower Pu inventory, which is also supported by the reported Cs-137 profiles. These results demonstrated that Pu could be applied as an ideal substitute of Cs-137 for soil erosion study in the future.</p

Accumulation of 137Cs in bottom sediments of the Curonian Lagoon

Measurements of activity concentrations and speciation of 137Cs in bottom sediments of the Curonian Lagoon were carried out in samples collected in 1999-2003. In addition, the sorption-desorption processes of caesium in disturbed bottom sediments of fresh and sea water systems were investigated in long-term experiments (up to 375 days) in order to better understand the caesium behaviour during the Baltic Sea water flooding events to the Curonian Lagoon. The modified Tessier method was used to study caesium associations with geochemical phases of bottom sediments. The effect of carbonate coatings of bottom sediments on the Cs sorption-desorption process was observed. The comparative analyses of 137Cs solid phase speciation in bottom sediments after 241 and 375 days of the sorption experiment with that of the 137Cs speciation, determined in the same sediment sample before the sorption experiment, indicated that after 375 days of sorption the equilibrium was not reached, however, the Cs distribution in geochemical phases was found to be close to equilibrium. The desorption experiments evidenced the release of caesium into solution from regular exchange complex and transfer from other phases to the frayed edge sites on the layered clay minerals with its further fixation in the crystal lattice. The remobilization of "fixed" caesium was not observed, on the contrary, the redistribution of caesium with its subsequent fixation in clay minerals was observed, and on a time scale its fixation kinetics was comparable with the sorption experiment. This study showed that flooding events of sea water contaminated with caesium can cause a significant accumulation of caesium in the bottom sediments of the Curonian Lagoon and result in the redistribution of 137Cs activity concentration in the bottom sediments from one area to another