The IAEA handbook on radionuclide transfer to wildlife

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Abstract

An IAEA handbook presenting transfer parameter values for wildlife has recently been produced. Concentration ratios (CRwo-media) between the whole organism (fresh weight) and either soil (dry weight) or water were collated for a range of wildlife groups (classified taxonomically and by feeding strategy) in terrestrial, freshwater, marine and brackish generic ecosystems. The data have been compiled in an on line database, which will continue to be updated in the future providing the basis for subsequent revision of the Wildlife TRS values. An overview of the compilation and analysis, and discussion of the extent and limitations of the data is presented. Example comparisons of the CRwo-media values are given for polonium across all wildlife groups and ecosystems and for molluscs for all radionuclides. The CRwo-media values have also been compared with those currently used in the ERICA Tool which represented the most complete published database for wildlife transfer values prior to this work. The use of CRwo-media values is a pragmatic approach to predicting radionuclide activity concentrations in wildlife and is similar to that used for screening assessments for the human food chain. The CRwo-media values are most suitable for a screening application where there are several conservative assumptions built into the models which will, to varying extents, compensate for the variable data quality and quantity, and associated uncertainty.

Introduction

Quantification of the transfer of radionuclides through foodchains to humans has long been a key focus of radiation protection. A key reference source of relevant transfer parameter values, the International Atomic Energy Agency (IAEA) Technical Report Series (TRS) handbook on transfer of radionuclides to human foodstuffs from terrestrial and freshwater systems, has recently been revised. This document, TRS 472 (IAEA, 2010), updates the previous handbook (TRS 364: IAEA, 1994). More recently, there has been a move away from radiation protection being solely anthropogenic to also consider protection of the environment as recognised by the International Commission on Radiological Protection (ICRP) in their revised Recommendations 2007 and the IAEA (2006) in their Fundamental Safety Principles and International Basic Safety Standards (IAEA, 2011a), all of which now include the need to protect the environment.

A number of approaches have been developed specifically to estimate the exposure of wildlife to ionising radiation, including frameworks being developed by the ICRP, 2003, ICRP, 2008, ICRP, 2009, USDOE (USDOE, 2002) and the ERICA Integrated approach (Larsson, 2007, Howard and Larsson, 2008). Some of these approaches have been used to address requirements in national legislation to demonstrate that the environment is protected from anthropogenic sources of ionising radiation (e.g. USDOE, 2002, USDOE, 2008, Canada, 2003, Copplestone et al., 2001, Copplestone et al., 2003, Strålsäkerhetsmyndigheten, 2009, Radiation and Nuclear Safety Authority, 2001).

To assess the exposure of wildlife to ionising radiation an approach is needed which contains the following components: (i) transfer of radionuclides to wildlife; and (ii) dose conversion coefficients relating internal and media activity concentrations to estimate absorbed dose rates to wildlife. The risk to wildlife is then considered using knowledge of the biological effects of ionising radiation (Copplestone et al., 2008, Andersson et al., 2009, ICRP, 2009).

The IAEA initiated the Biota Working Group (BWG) within its Environmental Modelling for Radiation Safety (EMRAS I: 2003–2007) programme to compare and improve the growing number of approaches to estimate the exposure of wildlife (both plants and animals) to ionising radiation. Through model testing and comparison using scenarios, the BWG demonstrated that the dosimetric components of the various models available gave broadly comparable results, but that differences in the transfer components resulted in large variation in predicted whole organism activity concentrations and resultant internal doses (IAEA, in press, Vives I Batlle et al., 2007, Beresford et al., 2008a, Beresford et al., 2009, Beresford et al., 2010, Yankovich et al., 2010a). These conclusions were supported by the outcome of the PROTECT EURATOM project (Howard et al., 2010) which compared the currently available approaches (Beresford et al., 2008b, Beresford et al., 2010) and by the IAEA’s Coordination Group on Radiation Protection of the Environment (IAEA, 2011b). The BWG recommended that an international handbook on estimating transfer of radionuclides to wildlife, similar to the IAEA Technical Report Series Handbook TRS 472 (IAEA, 2010) for estimating transfer to human foodstuffs, should be produced by the IAEA to provide readily available quantitative information. In response under EMRAS II (2009–2011), Working Group 5 was created to prepare a TRS document on the transfer of radionuclides to wildlife.

The term used to refer to living organisms other than humans has varied over the years in radiation protection and radioecological literature. In 1992, the IAEA referred to plants and animals (IAEA, 1992) whilst the ICRP (2009) use the term ‘non-human species’ to refer to species other than humans. In many recent documents, the term ‘non-human biota’ has been used, but this term is rarely used in other areas of environmental protection. In the handbook the term ‘wildlife’ is used to refer to all living organisms and includes all non-domesticated plants, animals and other organisms including feral species (i.e. non-native, self-sustaining populations).

The ‘Wildlife’ TRS handbook provides generic transfer data for use in the radiological assessment of wildlife as a consequence of planned and existing exposure situations as defined by ICRP (2007). As an equilibrium approach is presented, these data are not directly applicable to emergency situations as they would need to be supplemented by information such as the extent of interception by plants and the often rapid initial changes in radionuclide mobility and bioavailability with time.

When undertaking radiological assessments for aquatic systems, sediment–water distribution coefficients (Kd) may be used to predict water or sediment concentrations from known sediment or water concentrations respectively. Previous IAEA documents have provided reviews of Kd values for marine (IAEA, 2004) and freshwater ecosystems (IAEA, 2009a, IAEA, 2009b, IAEA, 2010) so Kd values are not included in the Wildlife TRS.

For C and H, specific activity approaches are provided in the Wildlife TRS. The values are consistent with the approach used for human food chain modelling (IAEA, 2009a, IAEA, 2010) and are not considered here.

Section snippets

Categorising living organisms

It is clearly impossible to provide individual radionuclide transfer for the enormous range of living organisms. Therefore, representative or generic groups of organisms have been identified for different types of ecosystem. The categorisation used varies between different assessment tools with slightly different terms and definitions (Beresford et al., 2008b) and approaches to this are described below. For each of the predefined organism groups in an assessment tool there is a need to provide

Quantification of transfer

The most common approach to estimate radionuclide transfer to wildlife in assessment models uses a concentration ratio to predict the whole organism activity concentration from the activity concentration in the soil, water or air that often function as reservoirs for nutrients and contaminants (e.g. Copplestone et al., 2001, USDOE, 2002, Beresford et al., 2008a, Beresford et al., 2008b, Beresford et al., 2008c, Hosseini et al., 2008). Such simplistic ratios clearly do not take into account the

The online database

To facilitate the collection of data an online database (www.wildlifetransferdatabase.org) was established as a joint IAEA and ICRP initiative in collaboration with the International Union of Radioecology. The database has been used to provide CRwo-media values for both the Wildlife TRS and the ICRPs developing framework (ICRP, 2009). The online database provides a structured way to collate data from the scientific community on the transfer of radionuclides to wildlife.

CRwo-media values for

The CRwo-media tables

In the Wildlife TRS CRwo-media values for adult life stages are provided for terrestrial, freshwater, marine and brackish ecosystems. The complete tables in the Wildlife TRS are too extensive to be presented here since they comprise >800 element – wildlife group combinations. Prior to the publication of the Wildlife TRS the tables can be accessed through the online database (www.wildlifetransferdatabase.org).

CRwo-media values are presented by wildlife subcategory where possible. Subcategories

Extrapolation approaches

For screening assessments, there is a need to provide default CRwo-media values for many different radionuclide and wildlife groups. Existing models use a number of approaches to overcome the lack of CRwo-media values (e.g. Copplestone et al., 2003, Beresford et al., 2008a, Beresford et al., 2008b, Beresford et al., 2008c, USDOE, 2002). The CRwo-media tables in the Wildlife TRS only provide values where there are sufficient relevant data in the database. As the Wildlife TRS does not contain all

Discussion

The CRwo-media values compiled in IAEA (in-press) can be used to calculate the whole organism radionuclide activity concentration of wildlife in environmental risk assessments in three ways depending upon the requirements of the assessment:

  • a)

    generic average value using either the geometric or arithmetic mean;

  • b)

    conservative estimate using either the maximum value or applying the SD to derive an upper percentile to be decided by the assessor (e.g. 95th percentile);

  • c)

    probabilistic assessment using the

Acknowledgements

We would like to thank the many other contributors, acknowledged in the Wildlife TRS, in addition to the drafting group and major contributors listed here as authors, notably EMRAS WG5 participants. The contribution of CEH was supported under the Knowledge Exchange programme of the Natural Environment Research Council in the UK, grant no NE/H001417/1 - Radiation protection of the environment providing knowledge and skills to the user community.

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