Cesium-137 partitioning to wetland sediments and uptake by plants

Studies were undertaken to develop a conceptual model for conducting ecological risk assessment at the R-Canal, located on the Savannah River Site, Aiken, South Carolina. Soil profiles collected from within the canals indicated that the maximum 137Cs concentrations generally occurred at a depth between 2.5 and 7.5 cm. The original 137Cs deposits, the result of accidental releases in the early 1960's, were covered by newly formed organic and/or fluvial deposits. About 60p of the total 137Cs inventory in each core existed at the organic matter/mineral interface. Based on sequential extraction tests, most of the Cs in this layer was held by either amorphous Fe-oxyhydroxides or organic matter. Sequential extraction tests also indicated that almost half of the Cs was weakly bound to the soil (either exchangeable or associated with amorphous Fe-oxides), a percentage that is five times greater than reported at the Hanford Site. 137Cs distribution within the profile was controlled more when the 137Cs was released than by the composition (organic matter concentrations, mineralogy, particle size distribution) of the soil. Netted chain fern had greater plant : soil concentration ratios in drier terrestrial environments than in wetland environments. The cause may be related to the Cs existing in a more bioavailable form or to the better overall health of the plants under drier soil conditions. The average concentration ratio was greater for the netted chain fern 2.78±2.96 than for rice cutgrass 0.18±0.13. The overall average plant : soil concentration ratio, 1.05±2.01, was large and points out, yet again, that Cs bioavailability is greater on the SRS than at most other sites.