A comparison of sea water and fresh water in a study of sediment-water exchange of radionuclides

The interaction of contaminated fresh water sediment with the marine environment is one of the important processes taking place in estuaries. Sediments contaminated by discharges from nuclear facilities situated upstream of rivers may eventually reach the estuary zones where K-d, values may change dramatically for some radionuclides. In order to gain a better understanding of radionuclide behaviour in river systems and in estuarine processes, a 'naturally' contaminated river sediment has been used in a laboratory study of 'passive diffusion' from sediment cores to fresh water and sea water under similar physical conditions. The sediment contains up to 1000 kBq.kg(-1) dry weight of Cs-137 and about ten times less of Sr-90 and Pu-239,Pu-240. Th, results for Cs-137 show that the distribution coefficient, K-d, decreases with at least a factor of 4-7 if this fresh water sediment comes into contact with high salinity sea water.