Review of existing Australian radionuclide activity concentration data in non-human biota inhabiting uranium mining environments
|
|  Yüklə 0.94 Mb.
|
1.2Purpose and ScopeThis report provides a summary and evaluation of existing Australian radionuclide activity concentration data in non-human biota common to Australian uranium mining and milling environments. Sources reviewed include data published in peer-reviewed journals, internal government agency reports, data from uranium mining companies and other consultant’s reports that have been produced by a range of organisations over the past 40 years. Data was evaluated for its suitability for use in calculating whole-organism concentration ratios. Where possible, in the timeframes available to this project, a number of these whole-organism concentration ratios for terrestrial and freshwater wildlife groups have been calculated. An overview of these will be provided. Any significant data gaps or issues are discussed in order to assist with moving towards establishing a collection of Australian whole-organism concentration ratios. This will also assist with identification of appropriate Australian reference organisms and the implementation of a framework for assessment and protection of the environment, in an Australian context, which is compatible with international best practice.
1.3StructureThis report consists of four sections and four appendices. Following this introduction, Section 2 describes the concepts and approach taken in conducting this review. Section 3 outlines the data collection, review and evaluation process. Section 4 provides the conclusions and makes some recommendations for future work. Concepts and Approach1.4Terminologies1.4.1Non-human biota, non-human species or wildlife?The term used to refer to species other than humans has varied over the past 20 years. The ICRP use the term ‘non-human species’, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) use non-human biota, and the International Atomic Energy Agency (IAEA) have used a range of terms including, plants and animals (IAEA, 1992); non-human species (IAEA, 2010) and in their most recent document, which is still to be published (IAEA, in press), the IAEA will use the term ‘wildlife’ which relates to living species that are not domesticated and exist in natural habitats. In other publications ‘non-human biota’ has been used but this term is rarely used in ecotoxicology and other areas of environmental protection. It is noted that ARPANSA discussed non-human species in their previous publication on this topic (Doering, 2010) however in this current report the term non-human biota will be used, as agreed between DI and ARPANSA in 2011. Non-human biota includes any flora or fauna, endemic or introduced, that exists in natural habitats, and specifically in this report, Australian uranium mining or milling environments. This includes domesticated species such as sheep that graze on extensive areas of pastoral lease near uranium deposits or mining areas. Following the finalisation of this report it has been agreed that in the future environmental exposures of wildlife in the natural environment will be the terminology applied in the Australian radiation protection framework (ARPANSA, 2014). How data on domesticated species such as sheep are utilised when conducting environmental assessments in the future should be considered by the working group that is currently preparing the ARPANSA Safety Guide for Radiation Protection of the Environment under the direction of the Radiation Health Committee. 1.4.2Equilibrium concentration ratiosWhen undertaking radiological risk assessments one of the data components that is essential for such assessments are the organism-to-media concentration ratio (CR) values that are used to estimate whole-organism radionuclide activity concentrations in biota from those in environmental media. The CR values discussed in this report are all assumed to be in equilibrium in the environment between exposed biota and the environmental media which they inhabit. These CR values are particularly appropriate for assessments of long-term exposure scenarios. They are not appropriate for circumstances where there is variation in the radiological conditions (e.g. pulsed inputs of radionuclides or accidents) and alternative methods of quantifying transfer, including dynamic models should be considered. Given the aim of this project was to review existing Australian datasets for radionuclide activity concentrations in non-human biota inhabiting uranium mining environments and assess their use for calculating whole-organism CRs, it is important to understand the common approaches utilised within the international community to estimate whole-organism concentration ratios for non-human biota from a range of data sources. 1.4.2.1Whole-organism concentration ratiosThe whole-organism concentration ratio (CRWO-media) is a value used to quantify the equilibrium activity concentration between an environmental medium and the whole living organism. This may previously have been referred to as concentration factor or bioaccumulation factor. It generally does not include parts of the organism which might be contaminated by environmental media (soil, silt) such as the gut or pelt (IAEA, in press). The definitions of CRWO-media are as follows: For terrestrial biota:
Exceptions for terrestrial biota exist for chronic atmospheric releases of H-3, C-14, S-35 and radioisotopes of P, where: 
For aquatic biota: 
Additionally, in aquatic ecosystems, the distribution coefficient (Kd) describes the relative activity concentrations of radionuclides in sediment and water, where: 
The distribution coefficient can be used to predict radionuclide activity concentration in sediment from that in water, or vice versa, if data for either is lacking. During the course of this data review the relationship between sediment values and activity concentration in filtered water was not examined, nor applied to estimate radionuclide activity concentrations in either media if data was lacking. A summary of Kd values for Australian aquatic environments and their application to estimating media concentrations in the absence of data should be considered in the future.
1.4.2.2Tissue concentration ratiosThe tissue-media concentration ratio (CRtissue-media) is a value used to quantify the equilibrium activity concentration between an environmental medium and a specific biota tissue. Tissue-to-media CR should not be used in biota dose assessments in lieu of organism-to-media data. This is because radionuclide activity concentration (and thereby CR) for a specific tissue may be substantially less than, or greater than, that for the whole-body of the organism due to preferential uptake of certain radionuclides by certain tissues. Doering (2010) provided a short summary of existing CR data for Australian biota. These CRs were at the tissue-to-media level and came from a limited number of geographic regions, including the Alligator Rivers Region (Martin et al., 1998; Martin & Ryan 2004; Ryan et al., 2008; Bollhöfer et al., 2011), Maralinga (Giles et al., 1990) and some semi-arid regions of Australia (Johansen & Twining, 2010). It was expected during this review that much of the additional data would also be at the tissue-to-media level as the data was originally collected for the purpose of assessing ingestion dose to the ‘representative person’ consuming certain plant and animal tissues. Over recent years, at the international level, there has been a significant amount of work undertaken to assist in ‘unlocking’ some of this tissue data in order to facilitate the estimation of whole-organism-to-media CRs.
|
