BIOGEOCHEMISTRY OF RADIOIODINE
THE PROPOSED WORK COMPRISES A DETAILED INVESTIGATION OF THE ROLE OF BIOGEOCHEMICAL PROCESSES IN THE BEHAVIOUR OF RADIOIODINE IN AQUATIC AND TERRESTRIAL ENVIRONMENTS. SUCH PROCESSES SEEM TO BE DECISIVE FOR SPECIATION OF RADIOIODINE IN ENVIRONMENTS AND ARE THUS IMPORTANT FOR UNDERSTANDING OF MIGRATION BEHAVIOUR AND BIOAVAILABILITY OF RADIOIODINE IN SOIL SYSTEMS.
An investigation has been made of radioiodine speciation in aquatic and terrestrial systems, and in particular its conversion inter-organic bonds under the influence of biogeochemical processes. The role of enzymatically medicated reactions in the transformation of radioiodine into organic bonds has been studied. The necessary enzymatic systems seem to be produced by microorganisms which occur in surface aquatic and terrestrial environments. No iodine converting activity is found in materials from deeper aquifers. The iodination processes are reversible and proceed only under aerobic conditions. In anaerobic media, iodine is released from organic bords by continuation of the deiodination process, while iodination is abolished.
Iodine sorption in soils, mediated by the above processes, results in large retention times of radioiodine on its way from the atmosphere to groundwater, of the order of several 100 years. The iodine is lost if the soil is subjected to anaerobic conditions, such as waterlogging.
It was concluded that aquifers were effectively protected against infiltration of airborne radioiodine by an intact organic soil cover.
THE PRESENT KNOWLEDGE ON GEOCHEMISTRY OF IODINE IN SOILS INDICATES A STRONG ASSOCIATION OF THE ELEMENT TO ORGANIC MATTER. IN SURFACE FRESH-WATER A CONVERSION OF ADDED RADIOIODIDE INTO OTHER CHEMICAL FORMS WAS OBSERVED WHICH TURN OUT AS ORGANIC IODINE COMPOUNDS (BEHRENS, ENVIRONMENTAL MIGRATION OF LONG-LIVED RADIONUCLIDES, IAEA, VIENNA 1982). BY COMPARISON OF THE DIFFERENT CHEMICAL AND SORPTION BEHAVIOUR OF RADIOIODINE IN STERILIZED SURFACE FRESH-WATER OR SOIL VERSUS NATURAL MATERIALS A DECISIVE ROLE OF MICROORGANISMS FOR THE BEHAVIOUR OF THE ELEMENT WAS SUGGESTED (BEHRENS 1982; BORS ET AL., ATOMKERNENERGIE-KERNTECHNIK 44 (1984) 87 ; STRACK, ROLE OF MICROORGANISMS ON THE BEHAVIOUR OF RADIONUCLIDES IN AQUATIC AND TERRESTRIAL SYSTEMS AND THEIR TRANSFER TO MAN, BRUSSELS 1984).
STUDIES PERFORMED SO FAR HAVE SHOWN THAT UPTAKE OF RADIOIODINE BY MICROORGANISMS MAY PLAY ONLY A MINOR ROLE. THE MICROBIALLY MEDIATED REACTIONS RATHER APPEAR AS AN ENZYMATIC OXIDATION OF IODIDE RESULTING IN A CHEMICAL BOND OF THE IODINE ("IODINATION") TO ORGANIC SUBSTANCES WHICH ARE PRESENT IN DISSOLVED FORM AND AS SOLIDS IN SURFACE WATER AND WATER/SOIL SYSTEMS.
THE DETAILED PROCEDURES OF THE PLANNED WORK TO GAIN MORE INFORMATION ON THE BEHAVIOUR OF RADIOIODINE IN ENVIRONMENTS ARE:
- STUDY OF THE CONVERSION OF IODIDE INTO ORGANIC BONDS IN SURFACE AND SOIL WATER, ESP. IN RESPECT TO REDOX CONDITIONS.
- STUDY OF SORPTION AND DESORPTION PROCESSES OF RADIOIODINE IN SOIL/WATER MIXTURES BY BATCH AND COLUMN TESTS; STUDY OF THE RESULTING MIGRATION BEHAVIOUR OF RADIOIODINE BY COLUMN TESTS.
- CONFIRM THE CONJECTURE THAT CHEMISTRY OF RADIOIODINE IN ENVIRONMENTAL SYSTEMS IS DECISIVELY MEDIATED BY ENZYMATIC PROCESSES.
- EVALUATE AND DESCRIBE REACTION KINETICS OF RADIOIODINE CONVERSION AND EQUILIBRIA.
- DELIVER DATA FOR THE DESCRIPTION OF RADIOIODINE MIGRATION BEHAVIOUR IN AQUATIC AND TERRESTRIAL SYSTEMS AND BIOAVAILABILITY OF RADIOIODINE.