Environmental protection from ionising contaminants in the arctic

Project Information

EPIC

Grant agreement ID: ICA2-CT-2000-10032

Start date 1 November 2000

End date 31 October 2003

Funded under

• Programme for research, technological development and demonstration on "Confirming the international role of Community research,1998-2002"

Total cost € 637 859,00

EU contribution € 425 826,00

Coordinated by

NORWEGIAN RADIATION PROTECTION AUTHORITY
Norway

Deliverables

Transfer and dosimetric models for reference Arctic biota

Transfer models for reference Arctic biota: A review of the available literature has shown that there are few Arctic-specific concentrations ratios for freshwater biota. However, a proven dynamic model is available for describing the behaviour of selected radionuclides in abiotic and biotic components of freshwater ecosystems. For some radionuclides (Cs, Sr, P, Mn, Zn, I and Co) rates of uptake by fish are modelled using temperature dependent and ECOMOD includes some parameters derived from northern Russian lakes. These aspects of ECOMOD can therefore be said to be applicable to the Arctic. However, for other radionuclides and for invertebrates and aquatic plants non-Arctic specific empirical transfer ratios have to be used. Aquatic mammals and birds are not considered within the existing model. Although we have only considered modelling approaches for Arctic lakes these could be adapted to Arctic rivers in combination with an appropriate a river transport model. Marine Concentration factors values for many marine biota are available within international reviews. Whilst these tend to be for edible tissues it is possible that in some cases they could be transformed into whole body burdens using published distributions of radionuclides within organisms. However, they are not specific to the Arctic where transfer may be influenced by environmental factors such as low temperature, seasonal variation in light intensity and ice cover. Arctic–specific data have been collated for Cs, Pu, Sr and Tc from the open literature and are recommended to be used as supplementary information, although, in general, the collated Arctic concentration factors are similar to those for temperate environments. Dynamic models have been used for the prediction of radionuclide activity concentrations in Arctic marine species has been demonstrated. Allometric relationships have been used in several cases where empirical data were unavailable for model parameterisation. The preliminary model appears to give reasonable predictions for 137Cs and 239Pu and demonstrates the fact that high trophic level organism may take very long time periods to become equilibrated with ambient water concentrations. Such an approach could also be used to provide missing data for Arctic freshwater ecosystems. Marine contaminant transport models, some of which have been applied to the Arctic and include parameters of ice flow and formation, are reviewed. Terrestrial Data describing the transfer of radionuclides from soil–reference biota have been collated. The most abundant data were for radiocaesium and radiostrontium although many data for natural radionuclides were available from studies from the Arctic. No data were available for describing the transfer of some radionuclides to Arctic biota. Allometric-kinetic models were also used to try to provide estimates of transfer for radionuclide-biota combinations for which data were lacking using, where possible, soil–plant transfer parameters derived during the review. Predicted values were in good agreement with observed data for some radionuclides (e.g. Cs, U) although less so for others. However, for some radionuclides where comparison appeared poor there was relatively little observed data with which to compare and the developed models were very simplistic not considering all transfer pathways. There are no bespoke models to enable the dynamic prediction of radionuclide transfer to Arctic biota. One available human foodchain model includes limited parameterisation for Cs and Sr transfer in Arctic ecosystems. This has been relatively easily adapted to estimate 137Cs and 90Sr transfer to some Arctic biota and could be readily adapted to other radionuclide – reference organism combinations. However, there are many factors of Arctic ecosystems, which may influence radionuclide behaviour including short growing seasons, prolonged freezing of soil, and effects of low temperatures on biological rates. However, whilst the influence of some of these has been documented, they are not included within existing predictive models. If exposure to ionising radiation within Arctic terrestrial ecosystems is to be robustly predicted such factors must be fully understood and properly incorporated into models. Dosimetric models for reference Arctic biota: The new methodology, algorithms and the first version of the computer program for an estimation of internal and external exposure of various biota representatives are developed. The dose coefficients for 42 radionuclides of natural and artificial origin at various variants of external and internal exposures of biota in terrestrial and aquatic environments are calculated. At present time the first version of the computer program allowing carry out of such calculations is prepared. The methodology and algorithms of calculation can be used by the scientists engaged in researches in the field of radiation protection of an environment and by the decision makers in a case of radioactive environmental contamination.

Exposure assessment framework for referecne Arctic biota

The EPIC system consists of problem formulation stage and primarily of an assessment methodology that will allow an assessor to quantify the probable effect of radiation exposure to selected biota following a defined release of radionuclides. The considerations afforded the system development have also been limited in a geographical context to the European Arctic, and to a suite of 13 radionuclides selected to broadly represent: - Routine release scenarios; - Accidental releases and; - TENORM radionuclides. Terrestrial, freshwater and marine ecosystems have been studied. Lists of reference organisms were constructed based on the application of relevant selection criteria. The generic reference organism lists have been used as a basis for deriving appropriate environmental transfer data information and selecting suitable target geometries/phantoms for dosimetric modelling. Basic ecological information has been collated for each of the selected flora and fauna. The specific organism attributes that should be considered relate directly to the subsequent assessment of exposure. For example, information should be provided on habitat and the fractional occupancy of various organisms in their habitats. Several approaches have been employed in order to consider the transfer of radionuclides in the Arctic environment. In the first instance, datasets providing information on concentration ratios/factors have been collated for reference organism types and the suite of radionuclides. This exercise has allowed data gaps to be identified. In cases where data coverage is poor or non-existent, other methodologies have been employed. Such methods have included the application of allometric relationships and biokinetic models. Limitations in the application of concentration ratios have been explored. These essentially relate to problems in applying the method where sources to a compartment are numerous and the unsuitability of applying the approach to non-equilibrium situations. In light of these problems, further work was conducted in the development of fully dynamic models as exemplified by work with the model �ECOMARC� to allow activity concentrations in a herbivorous and carnivorous mammal to be derived. The method for deriving absorbed doses is based on an approximation describing the dose distribution defined using Dose attenuation and Chord distribution functions. External doses to organisms from radionuclides present in soil or in the water column are calculated using a variant of a simple formula for a uniformly contaminated isotropic infinite absorbing medium. A two-step method has been used for the estimation of external exposures at the interface of environments with different densities. In the first step, the kerma in a specified location is derived. In the second step, the ratio of the dose in an organism and the kerma is calculated for the different organisms and radionuclides. A computer model with a user-friendly interface has been developed to allow such calculations to be conducted. Radionuclide specific Dose Conversion Factors have been generated for all reference organism groups and a large suite of radionuclides including the 13 radionuclide selected within EPIC and radionuclides from natural series decay chains. The approach taken within EPIC with regards analyses of dose-effects relationships, was to collate and organise data around the reference organism categories and to focus on dose-rates and biological endpoints that are of relevance from the perspective of environmental protection. Data of dose-effects relationships on radiation effects in biota available from Russian language sources have been collated. The data are concentrated on the effects in radiosensitive species in terrestrial and aquatic ecosystems, such as mammals, fish, and sensitive groups of plants. Data have been organised under �umbrella� end-point categories, i.e.: morbidity, reproduction, mortality, cytogenetic effects, ecological effects, stimulation effects and adaptation effects. A general conclusion can be made, that the threshold for deterministic radiation effects in wildlife lies somewhere in the range 0.5-1mGy d-1 for chronic low-LET radiation. Preliminary scales defining the severity of radiation effects at different levels of chronic exposure for different organisms groups have been constructed. In addition, background dose-rates have been calculated for reference organisms in various ecosystems. In order to assess the potential consequences of exposures to radiation on non-human biota, arguably, two points of reference may be used. These are: - Natural background dose rates and - Dose rates known to have specific biological effects on individual organisms. The information collated within the EPIC project is consistent with this and, therefore, allows an evaluation of potential effects from a given dose-rate to be made.

Dose effects relationships for reference (or related) Arctic biota

One of the key objectives within the EPIC project was to compile and analyse the data relating to dose-effects relationships for flora and fauna in the Arctic and northern areas. The EPIC database �Radiation effects on biota� has been created to provide a scientific basis for establishing criteria on the protection of northern/Arctic wildlife from the effects of ionising radiation. The EPIC database contains information based exclusively on Russian/FSU experimental and field studies of the radiation effects on flora and fauna of northern/Arctic climatic zone. Chronic/lifetime exposures were the focus of the work, owing to the fact that such exposures are the most typical in radiological assessments for biota. In total, the EPIC database �Radiation effects on biota� contains about 1600 records from 435 publications. The database has been developed in the form of electronic EXCEL tables. The EPIC database consists of the following sub-databases: Radiation effects on terrestrial animals; Radiation effects on aquatic animals; Effects on terrestrial plants and herbaceous vegetation; Effects on soil fauna; Effects on microorganisms; lethal doses. The EPIC database information cover a very wide range of radiation dose rates to wild flora and fauna: from below 10-5Gy d-1 up to more than 1Gy d-1. The radiation effects registered in the EPIC database encompass effects from stimulation at low doses up to death from acute radiation syndrome at high doses. Based on information, compiled in the EPIC database, the preliminary dose-effects relationships were derived, providing the preliminary scale of severity of radiation effects at increasing levels of chronic radiation exposure. Further development of the methodology for assessing the radiation impact on wildlife will involve the structuring and synthesis of dose-effects relationships for different categories of wildlife and different types of ionising radiation to facilitate decision making processes. Results of the research can be used for support of decision-making on the ecosystem management in contaminated areas. In the long-term prospective these results can be used in the tasks on determination of permissible radiation impact on natural biota of the North. The results of the project are applicable for the identification of methodologies of dose estimates and radiological impact assessment on natural biota, ecosystem management and radiation protection in the areas of enhanced levels of natural/technogenic radioactivity in Europe. The main results of the project are disseminated by the distribution, to the scientific community and other interested organizations, of technical reports published by the participants of the EPIC project, and the publication of scientific papers in the international literature. The participants of the project made presentations of the project results to international symposia. In the prospective, the EPIC database can be published as a separate report/book, also an Internet version of the EPIC database can be developed.