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Workreport 2017-35



Sorption Experiments of Ag, Cl, Cs, I, Mo, Ni, Pb, Se, Sn, Sr and Tc ‒ Lastensuo Bog Samples and Poosjärvi and Kivijärvi Sediment Samples


Lusa, M.



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In the first section of this report the sorption experiments with Ag, Cl, Cs, I, Mo, Ni, Se, Sr and Tc in Lastensuo bog samples are presented. Especially the microbial effects on radionuclide retention was in addition investigated and discussed for the bog environment. At the second part of this report, the sorption experiments with Ag, Cl, Cs, I, Ni, Pb, Se, Sn, Sr and Tc in Poosjärvi and Kivijärvi sediment samples are presented shortly. For all reported nuclides recommendations for Kd values in bog environment and shallow lake sediments are given.

Radionuclide retention in mire environment is affected by various factors including speciation, redox potential, pH, complexing ligands, organic matter and clay content, as well as micro-organisms. Typically anionic radionuclides, like technetium, chlorine, iodine, selenium and molybdenum are poorly retained in mineral soils and therefore their retention in the upper organic layers of Lastensuo bog was expected elevated, compared to mineral soils or lower clay layers residing underneath the organic layers of Lastensuo bog. Cationic radionuclides (Cs+, Ni2+, Ag+, Sr2+) can exist associated with the mineral fraction of the bog more efficiently. However they can in addition exist as complexed or adsorbed on different organic cation exchange surfaces, depending on pH.

Cs+ was retained strongly on the clay minerals (illite) present in the bottom clay layer and in the organic gyttja and peat layers low level sorption of Cs+ on the pH dependent deprotonated carboxylic groups is expected. I- retention in anoxic layers was considerably lower compared to the upper oxic layers in which the microbial oxidation prior to I- incorporation into the organic matter and oxic accumulation of I- in bacteria takes place. In the clay and organic layers, SeO32- can be retained through microbial reduction involving aerobic and anaerobic bacteria and depending on prevailing pH conditions SeO32- can be abiotically retained on protonated nitrogen containing functional groups of organic matter. In addition, in the lowest clay layer SeO32- can be abiotically reduced in the presence of sulphides.  TcO4- retention on dried bog samples was found low, with mean Kd values below 10 L/kg DW and Cl- retention was in practise non-existent. MoO4- was retained most efficiently on middle peat layers of Lastensuo bog and Ni2+ on the gyttja layer. For Ag+ a relatively uniform retardation in all upper organic layers was found, with a somewhat reduced retention in the clay layer.Sr2+ had relatively high retention in the upper bog layers, especially in the surface moss. In the clay layer Sr2+ retention was low. Microbiota present in the bog layers was found to affect the retention behaviour of SeO32-, I-, Ni2+ and Ag+ on the sorption experiments conducted with sterilized samples. In addition, bacterial strains of Pseudomonas sp. PS-0-L, Pseudomonas sp. T5-6-I, Paenibacillus sp. V0-1-LW, Paenibacillus sp. B6-7-W, Rhodococcus sp. B6-7-CB and Burkholderia sp. K5-6-SY, isolated from the Lastensuo bog were able to remove Cs+, SeO32-, I-, Ni2+ and Ag+ from the solution, depending on incubation conditions. It is however possible, that microbiota affects also the behaviour of other studied radionuclides, especially TcO4- and MoO4-. Data from the microbial studies for these radionuclides is however not available for the Lastensuo bog samples.


Sorption, Retention, Mire, Bog, Lake sediments, Ag, Cl, Cs, I, Mo, Ni, Pb, Se, Sn, Sr, Tc


WR 2017-35_web (pdf) (25.2 MB)


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