Some Peculiarities Of Cs137 And Sr90 In Heterogeneouse System Soil-sorbent-plant
Some peculiarities of Cs137 and Sr90 in heterogeneouse system soil-sorbent-plant
V.V. Strelko1, D. Ellwood2, N.M. Openko1, S.V. Mikhalovsky3,
E.A. Diyuk1, D.I. Shvets1
1Institute for Sorption and Endoecology Problems, Ukrainian National Academy of Sciences,
General Naumov st. 13, 03680 Kyiv, Ukraine, e-mail: dshvets@ispe.kiev.ua
2University of Southampton, UK
3Brighton University, UK
After Chernobyl accident the major territories were contaminated with radionuclides of cesium, strontium, plutonium. Taking into account a large scale of contaminated territories sorption methods based on applying of sorbents of a various nature are the most reasonable for soils decontamination. As it was shown in our works earlier /1-3 / the most perspective sorbents for this purposes are carbon-mineral sorbents. In this work the possibility of remediation soils contaminated with radiocesium and radiostrontium with usage of new varieties of carbonmineral sorbents was investigated.
A number of soil additives including activated carbon, mineral adsorbents, its modified forms and composite materials were tested on their influence of 137Cs and 90Sr transition in plants. The influence of sorbent type, its amount and degree of soil activity on the process of soil decontamination was studied.
The field experiments were carried out in exclusion zone on the contaminated soil (activity was in the interval 24 – 1,2 kBq/kg).
Analysis of plants on the content of radiocesium and radiostrontium were made by radiometric method. Using obtained data medium values of content of radionuclides and confidence interval of values of determining parameters were calculated, the dispersion was about 10-12 %.
The field investigations showed not ordinary role of sorbents in migration of radionuclides in complicated system soil-plant. The decontamination of soils can be realized, at least, in two ways: at first, by selective binding of radionuclides in soil and lowering thus migration ability (mobility), secondly, by transition of radionuclides in green mass of plants. It
was shown that in the presence of mineral sorbent the accumulation of 137Cs and 90Sr by plant do not exceeds the natural process of phytoextraction, while the use of composite carbonmineral sorbents essentially increase concentration of radionuclides in plant green mass especially in the case of radiostrontium. Such effect was observed at the different activity of the soils.
It was established that the additions of carbonmineral sorbents into the soil increases the growth of the shoots and the harvest as whole. It is probably caused by presence in the sorbent matrix of some microelements, and also by the ability of the sorbents to remove from the soil the contamination of the herbicides and pesticides, which depress the growth and development of the plants.
During the test of a number of radioaccumulating plants was determined, that amaranth is a plant with the highest potential for extraction 137Cs and 90Sr from the contaminated soils, at first, due to the natural high specific radioaccumulative ability, secondly because of high productivity. The introducing of sorbent increases both these properties (K=6-8) of amaranth, that makes possible the usage of this plant for removal of cesium from the soil.
It was established that sorption additives introducing in the soil in dependence of its type variously influence on the migration of radionuclides.
The sorbents of binding type promote accumulation of radionuclides in its porous structure that leads to sharp decreasing of concentration of radionuclides in green mass of plants. Carbonmineral sorbent, on the contrary, increases migration of radionuclides in root zone of plants, that leads to considerable accumulation of radionuclides by plants and to increasing green mass.
References
1. Glushachenko O.A., Openko N.M., Konoplyasta E.A., Shvets D.I. The investigation of dynamic of sorption processes in the system "composite adsorbent-heterogeneous medium". Ext. Abstr., 23rd Biennial Conf. on Carbon, PennState, USA, 1997, Vol.2: 94-95.
2. Glushachenko O.A., Openko N.M., Konoplyasta E.A., Shvets D.I. Phytoremadiation of contaminated soils with carbonmineral adsorbents. Ext. Abstr., Eurocarbon, France, 1998, Vol.1:379-380.
3. Strelko V.V., Openko N.M., Diyuk E.A., Glushachenko O.A., Shvets D.I. Carboncontaining sorbents in the processes of phytoremediation of radiopolluted soils. Ext.Abstr., 24th Biennial Conf. on Carbon, 1999, Vol.2: 702-703.
Acknowledgments
The authors are deeply grateful to INTAS-Fund, which has provided financial support under projects "INTAS-UA-95-0132".
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