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- Author or Editor: D. McCubbin x
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Abstract
Since Pu(IV) and Pu(V) exhibit very different sediment sorption behaviour, the transport of Pu in the aquatic environment is dependant upon oxidation state and the rate of interconversion between the species. A number of laboratory experiments have been carried out to determine possible parameters which influence the rate of Pu redox reactions and the extent of sorption by suspended particulate in the marine environment. Results suggest that, although the initial sorption of Pu(IV) did not appear to be dependant upon the major cations present in seawater, the sorption of Pu(V) was decreased in the presence of Ca2+ and Mg2+ ions. Both the rates of oxidation of dissolved Pu(IV) and reduction of dissolved Pu(V) increased with increasing suspended particulate concentration.
Abstract
The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, 241Pu and 239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the 241Pu/239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and 241Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The 241Pu/239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea.
Abstract
Experiments have been carried out with well characterised laboratory solutions to establish the physico-chemical behaviour of a suite of radionuclides in the presence of humic and fulvic acids using single flat membrane ultrafilters. Because of the uncertainties associated with the methodology, an approach has been adopted using mass balance determinations to assess the performance of the ultrafiltration process and facilitate the interpretation of the fractionation data. The size distribution of radionuclide-ligand complexes are reported and the results are discussed in the context of interpreting environmental data with more confidence.
