Theoretical, experimental and field studies concerning reactions of radioisotopes with sediments and suspended particles of the sea Part C: Applications to field studies
Duursma, E.K.; Eisma, D. (1973). Theoretical, experimental and field studies concerning reactions of radioisotopes with sediments and suspended particles of the sea Part C: Applications to field studies. Neth. J. Sea Res. 6(3): 265-324
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, more
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| Authors | | Top |
- Duursma, E.K.
- Eisma, D., more
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| Abstract |
With the help of a number of national institutions a cooperative study was made of the radionuclide sediment behaviour of 59 characteristic marine sediments. The sediment samples were obtained from the sea floor of the three oceans, the Arctic Seas, the Baltic Sea, the North Sea, the Mediterranean, the Black Sea and the Red Sea. The radionuclides studied were 90Sr, 137Cs, 65Zn, 60Co, 95Zr/Nb, 54Mn, 59Fe, 106Ru, 147Pm and 144Ce. Only with Mediterranean sediment the behaviour of 240Pu, 45Ca, 86Rb and 210Pb was investigated. The sediment composition has been investigated for clay minerals in different grain-size fractions, for median grain size and sorting, for specific surface, for exchange capacity, for organic matter, and for the extractability of the ions Na, K, Ca, Mg and Fe with acetic acid NH4-acetate, 0,1 N HCl, 20% HCl, and concentrated HCl. Each of the parameters of the sediment composition has been related to the distribution coefficient of sorption which characterizes the radionuclide sediment behaviour. The best relationships were found with the base-exchange capacities and the specific surface values of the sediments. For the whole group of sediments, the ration between the distribution coefficient and the base-exchange capacity increases in the order 90Sr, 45Ca, 240Pu, 137Cs, 65Zn, 86Rb, 60Co, 95Zr/Nb, 54Mn, 59Fe, 106Ru, 210Pb, 147Pm, 144Ce; however, also an increasing deviation from the mean ratio. Strontium sorption is not related to the CaCO3 content of the sediment; 137Cs sorption has some relationship with the potassium and illite contents of the sediment. The experimentally defined half-time of sorption and the correlation of distribution coefficients with the characteristics of the sediments, made it possible to distinguish some of the sorption reactions such as isotope exchange (90Sr), ion exchange (137Cs, 65Zn), precipitation (95Zr/Nb, 59Fe), and a mixture of precipitation, ion exchange and formation of compounds (60Co, 54Mn, 106Ru, 147Pm, 144Ce). Although the sediments with relative high organic matter concentrations did not have elevated sorption distribution coefficients for all the radionuclides, the organic matter did increase the base-exchange capacity of the sediment, and to this parameter the distribution coefficients were more or less related. In anoxic sediments, the sorption distribution coefficients are slightly different, for example for 59Fe and 54Mn lower, and for 65Zn, 90Sr and 60Co higher than as determined for the same sediment under oxygenated conditions. For one river sediment and some of the radionuclides, sorption and loss were investigated in river sediments entering the sea. Sorption and loss could be observed by following the shifts of the distribution coefficients. For 2 marine sediments the radionuclide binding by different grain-size fractions was investigated. The fractions larger than 64 µm had negligible amounts of radionuclides, in the other fractions of smaller grain size, the distribution was different for different isotopes and sediments. Diffusion coefficients in packed sediment layers may be determined by dividing the diffusion coefficients of a non-sorbed ion, such as Cl-, by the distribution coefficient of sorption of a radionuclide. This diffusion applies only for the physico-chemical migration in a sea bed, where both molecular diffusion in the interstitial water and side reactions with the sedimentary particles are encountered. As these diffusion coefficients are mostly very low, it is quite possible that reworking of the sediment or sedimentation of new material may obscure this type of diffusion. The results of these studies may be applied to description and prediction of the behaviour of various radionuclides in sea-water sediment systems. Using these data together with knowledge on the hydrography and sedimentology of an area, it may be possible to predict some of the consequences of future waste-disposal practices in this area.As the radionuclides investigated are also indicators of the behaviour of their stable counterparts of similar physico-chemical forms, the results have an equal importance in the field of metal pollution in the marine environment, a difference being that metal accumulation is not affected by decay. |
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