Recultivation of Soils
Development of Biological Methods for Recultivation of Soils Polluted with Radionuclides.
Tech Area / Field
3 Approved without Funding
Research Center of Toxicology and Hygienic Regulation of Biopreparations, Russia, Moscow reg., Serpukhov
- All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
Project summaryBRIEF DESCRIPTION OF THE PROJECT GOALS
The problems of remediation of areas contaminated with radioactive substances under the Chernobyl Nuclear Power Plant (ChNPP) accident, other radiation accidents as well as activities of some enterprises have became especially urgent in last decade. The ChNPP accident alone resulted in contamination of millions of hectares in the former USSR. It became impossible for people to reside in vast territories owing to high density of radioactive contamination.
As is known, at present the environment being subjected to ChNPP accident is polluted by radioactive isotopes such as cesium-137, strontium-90 and plutonium-239.
The challenge of remediation problem is in the fact that, first, it is necessary to decontaminate millions of hectares and, second, that known techniques of soil decontamination are extremely labour-consuming and expensive.
A most known technique consists of removal of upper contaminated soil layer. The problem of utilization and burial of colossal amounts of radioactive wastes, i.e. removed soil, becomes practically insolvable since it requires creation of a very great number of specially equipped burial-grounds.
Though the chemical techniques for contaminated soil treatment reduce amount of radioactive wastes, but they considerably increase the remediation cost as compared to the above method.
Moreover, using such decontamination technique a fertile ground layer is disposed and large areas are put aside from agricultural circuitry. That is why a cost for remediatian is very high for any country.
In this connection biological method can become the most promising for soil remediation.
Briefly, biomethod is based on taking advantage of biological objects such as earthworms, biohumus (biologically active organic fertilizer), insect chitin which accumulate or bind radionuclides and influence directly that is shown in a number of publications
Indirect effect could be related with properties of biohumus, chitin and its derivaters. In a number of papers it was shown that humic acids of biohumus bind radionuclides and form insoluble helate complexes preventing their migration through trophic chains. Besides, inoculation of biohumus instead of manure leads to soil neutralization. Neutral medium in soil reduces mobility of radionuclides and their penetration into plants and underground waters. In mis way a fixation of pollutants in soil can be reached.
The advantages of biomethod include:
- low cost and labour-intensity as compared to the above methods;
- environment friendly technology not damaging soil;
- small amount of radioactive wastes and because of this low cost of their elimination;
- keeping fit fertile ground layer for farther agricultural activities.
The goal of the offered project is development of technology for biological deactivation of soils polluted with radionuclides.
For mis Project implementation the following questions are supposed to be solved:
- evaluate an efficiency of radionuclide accumulation by earthworms and estimate the upper limit of radionuclide concentration at which earthworms can be used for remediation;
- evaluate an efficiency of radionuclide fixing by biohumus and chitin to reduce radionuclide transition to agricultural plants;
- study radionuclide migration through the initial segment of the trophic chain soil-water-microoraamsms-fungi-plants-earthworrns;
- extend the existing radionuclide analysis method as applied to the set of problems;
- make experimental verification of the bioremediation method for soils with various content of real contaminants under laboratory and field conditions;
- develop recommendations on using biological methods and techniques for utilization of radioactive wastes under bioremediation.
TECHNICAL APPROACH AND METHODOLOGY
The work planned to be implemented under the project would be provided by the experience of scientific personnel of the ARRUM acquiring at acimination of the ChNPP accident consequences and environment monitoring, while the development of bio-remediation techniques would be based on the experience of the RCT&HRB gained at: development of biological technology for remediation of soil polluted by toxicants such as polyphenyls, oil products and phenols; vermicomposting sludge from municipal treatment plants containing high concentrations of heavy metals; ecological monitoring on integrated toxicity of soil in Serpukhov (Moscow region) using biotesting; processing organic wastes of agriculture and industry with use of special line of earthworms.
The RCT&HRB possesses with collection of special lines of earthworms as well as collection of microorganism - biodegraders. Under development of biotechnology for remediation of soil polluted by radionuclides the main role belongs to earthworms. For this purpose specially selected line of earthworms - "Red Obolensk hybrid" (hybrid of industrial line of earthworms Eisenia foetida) - is used. It can be used for all the year round breeding and introduction into polluted soils.
The upper lay (5 cm thickness) of soil polluted with radionuclides is removed by a bulldozer into clamps. Earthworms are inoculated into the clamps filled with wet soil, and under their vital activity the worms pass radioactive substrate through their digestive tract many times. Incidentally, as it was obtained in preliminary experiments, radionuclides are accumulated inside earthworms in higher concentrations than in soil. After one - four months of exposure (in dependence of initial concentration of radionuclides) earthworms are removed from the clamps together with the soil. At the RCT&HRB it is developed a method to collect the worms with use of a bait, there is "know-how".
It should be taken into consideration that radionuclides in polluted soil are both in water-soluble ion form and in corpuscle one as separate particles. Radionuclides in ion- form are cumulated inside worms much better. To increase the effectiveness of soil deactivation it is proposed to use specific strains of microorganisms - oxidants and lower fungi which transform radionuclides into ion-form and absorb them on a cellular surface. The worms, passing soil through their digestive tract, these microorganisms and cumulate radionuclides within their organism. The optimum period for accumulation of radionuclides from polluted soil by earthworms is about two months.
Under deactrvation of soil the organic wastes (manure and plant residues which also are polluted with radionuclides) should be inoculated into polluted soil to provide normal vital activity of earthworms. The wastes are digested by earthworms into biologically active fertilizer - biohumus.
It is also proposed to use different biosorbents such as chitinase, chitin powder of crustaceous and bentonite clay. Biological methods (as other known methods) do not make possible to remove total amount of radionuclides from soil. Therefore residual amount of radionuclides is proposed to bind in soil with biosorbents or biohumus produced by earthworms. Biohumus consist of humus acids (28-32%) which are bound with radionuclides into helate complexes. Thanks to this fact radionuclides do not penetrate into growing plants (agricultural produce).
However, to perfect the whole clean up technology it is needed to carry out some experiments.
It is planned to use in laboratory investigations real samples of soil polluted under ChNPP accident where the soil is contaminated by radionuclides on the depth up to 5 cm.
Cesium-137 comes to 95-99% of total radionuclides amount. That is why measuring cesium-137 in soil samples will be conducted mainly. It is proposed to use soil samples from 30-km zone of ChNPP, Krasnogor'e district and Novo-Zybkov district of Bryansk region with special radioactivity on cesium-137 as 12,34 Вк/g and 4,39 Вк/g accordingly.
Clean up technology will be examined under field-scale conditions with use of earthworms, microorganisms and biosorbents. A degree of clean up by biological method and optimum time rate for deactivation of soil contaminated by radionuclides will be estimated.