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Remediation of Radiation-Contaminated Soils

#A-1671


Remediation of Contaminated Soils in Zones of Radioecological Tension by Water-Retaining Polymers

Tech Area / Field

  • CHE-POL/Polymer Chemistry/Chemistry
  • ENV-RED/Remediation and Decontamination/Environment

Status
8 Project completed

Registration date
08.09.2008

Completion date
25.05.2012

Senior Project Manager
Savinova N V

Leading Institute
Institute of Hydroponics Problems, Armenia, Yerevan

Supporting institutes

  • Yerevan Institute "Plastpolymer", Armenia, Yerevan

Collaborators

  • Agriculture and Agri-Food Canada, Canada, ON, Ottawa

Project summary

Project GoalsTo provide new means and procedures for remediation of contaminated soils through regulation of biological migration of man-made anthropogenic radionuclides 137Cs and 90Sr by water-retaining polymers in systems water – soil – plant and water – nutrient solution – plant in zones of radio-ecological tension.

The possibility of radionuclides-related contamination of lands at agricultural holdings defines the necessity to apply special protective means/measures in plant growing. Soils possess high adsorptive capacity towards radionuclides and present the initial units of radionuclides migration into agricultural produce. Nowadays the sources of soil contamination embrace nuclear tests, radiation accidents and incidents, as well as operation of Nuclear Power Plants (NPPs). Even allowable releases from atomic industry entities and nuclear power engineering facilities gradually cumulate in soils and then penetrate into agricultural produce. The presence of a functioning a NPP and prospects to expand nuclear engineering elevate the possibility of radionuclides-caused soil contamination in Armenia as well. Therefore, constant monitoring and remediation of contaminated soils, in case of necessity, is urgent for countries throughout the world, especially for Armenia as a country with the limited area for agricultural crop production.

One of important aspects of the problem related to contaminated soils remediation is elaboration of protective actions aimed at reduction of biological migration of radionuclides in a system water – soil – plant. The agricultural radioecology has acquired significant experimental materials on modes decreasing the penetration of radionuclides from soils to plants. A number of agrochemical and land treatment techniques are elaborated: application of mineral and organic fertilizers, clayey materials, liming of soils, changes of irrigation regimen, burying of upper layers of soil in under layer. Amongst the man-made radionuclides 137Cs and 90Sr exert long-term after-effects of radionuclide caused contamination: for 137Cs the half-life 30.1 years, while for 90Sr the half-life 28.6 years. The pass of radionuclides, in particular 137Cs and 90Sr, occurs from the soil solution and irrigation water through the root system of plants. Ionic absorption has a specific part in this process of radionuclide transition from the soil into a plant. Radioactive cesium absorbance significantly decreases with the increase of potassium ions concentration in soil solution. This is confirmed by research performed in Russia and Belarus after the accident at the Chernobyl NPP. According to data of pilot research, application of potash fertilizers significantly retained the transfer of radioactive isotopes into plants. Currently application of potash fertilizers is the main agrochemical treatment mode to limit the pass of 137Cs from soil into plants. The elevation of Ca2+ ions concentration in soil solution facilitates the decrease of 90Sr accumulation by plants due to increased “concurrence” of these ions. The transition of 137Cs and 90Sr from soils into plants depends also on the type of soil. In Armenia the higher is the locality above sea level, the greater the rainfall, - appropriately the higher is the concentration of man-made radionuclides in soils. According to the content of man-made radionuclides soils make the following row: mountainous grassland soils > forest > black earth > chestnut >brown soils.

Recently the Yerevan Plastpolymer Institute jointly with the Institute of Hydroponics Problems of the NAS RA performs the research works on application of high-water-swellable polymers for plant growing under conditions of hydroponics. The preliminary studies demonstrated that upon application of Supersorbent-87 synthesized at Plastpolymer Institute for plant growing there was observed an increase of 137Cs and 90Sr content in plant biomass.

The proposed Project mainly aims to achieve control on migration of radionuclides in a system water – soil – plant due to counter ions variation in the superabsorbents. The task of the Project to regulate the migration of radionuclides will be achieved by varying the counter ions in a polymer polyelectrolyte on the base of Vinyl acetate copolymers. Copolymers proposed in the Project are capable to absorb the ion of one metal more efficiently than ions of other metals. Chemical binding with the copolymer hinders leaching of radioactive metal, preventing migration of radionuclides to deeper soil layers and ground waters and decreasing contamination of the environment. Proposed studies will allow to synthesize a polymer capable to absorb radionuclides out of water and soil, to cumulate in trees, which are known by the active radionuclide absorbing ability and would serve in this Project as a “green barrier” and prevent further spread of radionuclides in the environment. Another task of the Project is obtaining polyelectrolytes with the defined counter ion which will be preliminary applied to the root-inhabited media in order to reduce radionuclides migration from soil or nutrient solution into plants.

For Project implementation it is planned to perform synthesis, radio- and agrochemical, biological studies, in particular:

  1. adjustment of methods for obtaining new polymers;
  2. development of new polymer sorption-active materials containing fillers (kaolin, pearlite, etc.);
  3. studies on physical-chemical and physical-mechanical properties of polymer materials;
  4. growing different varieties of plants (trees saplings, melon and gourds, medicinal plants) under conditions of hydroponics and soil with the application of a polymer in root-inhabited media in different zones of radioecological tension (with the radius of 2-15 and 30 km from the Armenian NPP);
  5. determination of both quantitative and qualitative productivity of plants depending on the type and quantity of polymer material, water regimen (number, terms and rate of irrigation);
  6. determination of radionuclides content in a system water – soil – plant in the vicinity of the Armenian NPP (zone radius: 2-15 km), as well as under hydroponics conditions (zone radius: 30 km) in a system water – nutrient solution – plant;
  7. determination of migration and accumulation of radionuclides in soil layers of different depth, under-ground and over-ground parts of plants depending on application of the polymer;
  8. revealing the dependence of redistribution of radionuclides in systems water – soil – plant and water – nutrient solution – plant on the type and quantity of a polymer material, variety of a plant and irrigation regimen;
  9. establishment of a correlation between the structure, physical-mechanical properties of polymers and the radiochemical characteristics of plant raw material.

It is known that the majority of high-swelling polymers lose the swelling ability when taken from laboratory conditions to the soils. Obviously repeated tests for effectiveness are required under real-nature conditions. In a controlled artificial medium the closed hydroponics system allows distinct revealing of the effects of polymers to growth, development, productivity and radio-biochemical characteristics of plants.

Project findings will ensure further development of research and technologies of Superabsorbents obtaining, growing plants with the low content of radionuclides. Project main outcomes will also allow to propose new models for stage-by-stage remediation of agricultural lands contaminated by radionuclides. After the Project implementation the obtained Superabsorbents will be proposed for further commercialization.

Project goal will be achieved by joint efforts of a unified research team of highly professional scientists from such leading Armenian organizations as the Institute of Hydroponics Problems NAS RA and the Yerevan Institute Plastpolymer. Yerevan Institute Plastpolymer has a long-term successful experience of collaboration within ISTC (ISTC Projects A-183, A-359 A-948, and A-1358). The research team from the Institute of Hydroponics Problems involves highly professional specialists who have a long-lasting experience in cultivation of numerous medicinal, essential oil and other plants under conditions of the artificial medium, as well as in studies on agro-radiochemical and physiological-biochemical peculiarities of plants, monitoring of radionuclides in a system water – soil – plant.

Project related methodology includes known methods and methods developed by the team researchers for the synthesis of polymers, determination of radionuclides in soils and plants, methods for plant growing under conditions of hydroponics, in the soil and greenhouses.

In accordance with the aims of the ISTC during the implementation of this project the tasks will be performed to re-orient the activity of scientists earlier engaged in the sphere of defense research and industry towards the solution of problems relevant to environmental protection; to integrate Armenian scientists into the international research collaboration; to provide assistance in solution of national and international problems on protection and remediation of lands.

The role of Foreign Collaborators might include rendering methodic recommendations on radionuclides determination, joint discussions of research findings and information exchange in the course of Project implementation, providing comments to technical reports, joint publications.


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