Registration Dossier

Administrative data

Endpoint:
distribution modelling
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Report published by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. It follows generally accepted scientific principles and can be considered as reliable. The report examines the influence on human and the environment by long-term emissions of long-living radioactive iodine isotopes. Thus, it can be expected that the findings are adequate for the environmental assessment of the lifecycle of stable iodine.

Data source

Reference
Reference Type:
secondary source
Title:
Ableitung von radioökologischen Parametern aus dem langfristigen Eintrag von IOD-129
Author:
R. Michel, K.Klipsch, Th. Ernst, M. Gorny, D. Jakob, J. Vahlbruch, H.-A. Synal, C. Schnabel
Year:
2004
Bibliographic source:
Abschlussbericht Vorhaben StSch 4285, BMU – 2004-650, Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit, Arbeitsgruppe RS I 1, ISSN 1612-6386
Report Date:
2004

Materials and methods

Model:
other: Steady-state model assuming complete mixing of the compartments. Derivation of inventories based on the weighted average ratio of iodine contents of the ocean and marine sediment.

Results and discussion

Percent distribution in media

Air (%):
0
Water (%):
0.5
Soil (%):
0
Sediment (%):
32.2
Biota (%):
0
Other distribution results:
About 67% of total iodine are expected to be associated with igneous rocks in the Earth's crust. A further differentiation of the atmospheric distribution between gas phase and aerosol is very difficult due to the high reactivity and complexity of the atmospheric chemistry of iodine.

Any other information on results incl. tables

Michel et al. consider in their report on the natural lifecycle of iodine an extented and modified model developed by Fabryka-Martin in 1984 on basis of a steady-state model for the geochemical lifecycle of iodine by Kocher (Kocher, 1981; Fabryka-Martin, 1984). Finally, Schmidt added based on the known global ration the inventories of iodine-127 to the model, since Fabryka-Martin and Kocher were focussed on the distribution of the isotope iodine-129 (Schmidt, 1998). In both models complete mixing of the compartments is assumed. Major changes are the inclusion of the compartments igneous rocks and sediments (lithosphere), which are in no active exchange with the ocean, as well as the assumption that these compartments are in exchange with deep groundwater and the atmosphere only. Within the model about 95% of the global iodine inventory is assumed to be stored in the lithosphere with a mean residence time of more than 108years. An additional fraction of about 4% of total iodine is expected to be bound in recent ocean sediment. The mean residence time for this compartment is estimated to be about four million years. The remaining iodine (approx. 1%) is available for the lifecycle with the ocean considered to be the major reservoir.

In this model significant pathways are the migration of iodine from the lithosphere to the atmosphere and the hydrosphere (deep groundwater) by volcanic activities, combustion of fossil fuels and the weathering of rocks. Furthermore the exchange between recent ocean sediments and the deep-ocean as well as inner-oceanic mixing are important transport processes within the marine compartment. In addition, iodine is transferred from the freshwater segment to the ocean. The mixed-layer of the ocean is in a constantly exchange with the marine atmosphere by evaporation, sea spray, biogenic emissions plus dry and wet deposition in return. By different atmospheric processes iodine is distributed and transported to the pedosphere. The atmospheric and pedospheric exchange occurs by dry and wet deposition and by evaporation of iodine as such or as biogenic emission. Finally, the biosphere takes up iodine from hydrosphere and pedosphere and loses iodine by evaporation, decomposition as well as excretion to the atmosphere and pedosphere.

The inventories and fluxes were derived based on the asumption that the weighted average for ocean and sediments is 5.5x10^-13. From this value a ratio for the deep ocean can be calculated which is used as input parameter for the model. Global inventories and fluxes are shown in the attached figure.

References:

Fabryka-Martin J, Bentley H, Elmore D, Airey PL (1984). Natural iodine-129 as an environmental tracer, Geochim Cosmochim Acta, 49, 337-347.

Kocher DC (1981). A dynamic model of the global iodine cycle and estimation of dose to the world population from releases of Iodine-129 to the environment, Envt Intl, 5, 15-31.

Schmidt AC (1998). 129I und stabiles Iod in Umweltproben - Qualitätskontrolle von Analysenmethoden und Untersuchungen zur Radioökologie und zur retrospektiven Dosimetrie, Dissertation, University Hannover.

Applicant's summary and conclusion

Executive summary:

For several decades the geochemical lifecycle of iodine has been in the focus of the scientific community. Long-living isotops of iodine are emitted by humans since 1940s, and therefore modelling of the environmental fate of these emissions is strongly required to esteimate the potential exposure to humans and the environment.

The report of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety is the latest summary of the findings on the fate of radio-iodine. As the half-life of the considered isotops (iodine-129) is about 16 million years, the results of this report can also be expected to be adequate and relevant for the assessment of the environmental fate of stable iodine.