GEOCHEMICAL ASSOCIATIONS OF SELLAFIELD-DERIVED RADIONUCLIDES IN SALT-MARSH DEPOSITS OF THE SOLWAY FIRTH

This paper describes a study of the geochemical associations of Sellaf ield waste radionuclides in saltmarsh sediments from south-west Scotla nd. The contaminant radionuclides are transported to this environment in association with particulate material and Cs-137 was found to be pr edominantly (80-98%) non-extractable, In the case of Pu239+240 there w as a redistribution from the oxalate extractable oxide fraction to the pyrophosphate extractable organic fraction as a consequence of on-sho re transfer of contaminated sediment. The relatively aggressive nature of the chemical extractants required to remove the radionuclides from the sediments suggests that they were in a form which was unlikely to result in their being released into the aquatic environment or taken up by plants. Plutonium had a greater potential mobility or bioavailab ility than Cs. Values of KD for the desorption of 137Cs from the sedim ent by freshwater, groundwater and seawater were all approximately 10( 5) L kg(-1), confirming its immobility in this environment. The desorp tion K-D values for stable Cs-133 were all approximately 10(6) L kg(-1 ), so the stable Cs did not have a significant influence on the radioc aesium in this sediment.