Ensuring robust radiological risk assessment for wildlife: insights from the International Atomic Energy Agency EMRAS and MODARIA programmes

In response to changing international recommendations and national requirements, a number of assessment approaches, and associated tools and models, have been developed over the last circa 20 years to assess radiological risk to wildlife. In this paper, we summarise international intercomparison exercises and scenario applications of available radiological assessment models for wildlife to aid future model users and those such as regulators who interpret assessments. Through our studies, we have assessed the fitness for purpose of various models and tools, identified the major sources of uncertainty and made recommendations on how the models and tools can best be applied to suit the purposes of an assessment. We conclude that the commonly used tiered or graded assessment tools are generally fit for purpose for conducting screening-level assessments of radiological impacts to wildlife. Radiological protection of the environment (or wildlife) is still a relatively new development within the overall system of radiation protection and environmental assessment approaches are continuing to develop. Given that some new/developing approaches differ considerably from the more established models/tools and there is an increasing international interest in developing approaches that support the effective regulation of multiple stressors (including radiation), we recommend the continuation of coordinated international programmes for model development, intercomparison and scenario testing.

Towards an ecological modelling approach for assessing ionizing radiation impact on wildlife populations

The emphasis of the international system of radiological protection of the environment is to protect populations of flora and fauna. Throughout the MODARIA programmes, the United Nations' International Atomic Energy Agency (IAEA) has facilitated knowledge sharing, data gathering and model development on the effect of radiation on wildlife. We present a summary of the achievements of MODARIA I and II on wildlife dose effect modelling, extending to a new sensitivity analysis and model development to incorporate other stressors. We reviewed evidence on historical doses and transgenerational effects on wildlife from radioactively contaminated areas. We also evaluated chemical population modelling approaches, discussing similarities and differences between chemical and radiological impact assessment in wildlife. We developed population modelling methodologies by sourcing life history and radiosensitivity data and evaluating the available models, leading to the formulation of an ecosystem-based mathematical approach. This resulted in an ecologically relevant conceptual population model, which we used to produce advice on the evaluation of risk criteria used in the radiological protection of the environment and a proposed modelling extension for chemicals. This work seeks to inform stakeholder dialogue on factors influencing wildlife population responses to radiation, including discussions on the ecological relevance of current environmental protection criteria. The area of assessment of radiation effects in wildlife is still developing with underlying data and models continuing to be improved. IAEA's ongoing support to facilitate the sharing of new knowledge, models and approaches to Member States is highlighted, and we give suggestions for future developments in this regard.

Protection of the environment

The International Commission on Radiological Protection's (ICRP) system to protect the living components of the environment is designed to provide a broad and practical framework across different exposure situations. The framework recognises the need to be able to demonstrate an adequate level of protection in relation to planned exposure situations, whilst also providing an ability to manage existing and emergency situations in an appropriate way. In all three exposure situations, the release of radionuclides into the natural environment leads to exposures of non-human biota (wildlife), as well as having the potential for exposures of the public. How the key principles of the ICRP system of radiological protection apply in each of these exposure situations will be discussed. Using examples, we will demonstrate how the overall approach provides a mechanism for industry to assess and demonstrate compliance with the environmental protection objectives of relevant (national) legislation, and to meet stakeholder expectations that radiological protection of the environment is taken into consideration in accordance with international best practice. However, several challenges remain, and these will be discussed in the context of the need for additional guidance on the protection of the environment.

Characterising radium-226 particles from legacy contamination to support radiation dose assessments

Radioactive particles are physically discrete sources of radioactivity that have been released into the environment as a result of past emergencies, events and practices. As the release of radioactive particles is often unplanned, the source term has not been characterised, and the potential radiation doses have not been prospectively assessed. If a plausible exposure pathway exists, radioactive particles in the environment may present a hazard to the public depending on their radiological, physical and chemical characteristics. Given their physically discrete nature, standard assessment approaches such as dispersion and transfer modelling of liquid and gaseous radioactive releases, are not appropriate for radioactive particles. The challenge for national regulatory authorities is to calculate potential radiation doses from unplanned releases of radioactive particles into the environment, assess whether the doses are relevant to radiological protection and decide whether actions are required to reduce potential doses. To address this challenge, this paper presents the approach being adopted to radiologically, physically and chemically characterise Ra-226 particles from a contaminated legacy site using gamma spectrometry, optical macroscopy and SEM-EDS. The use of particle characterisation data to support radiation dose assessments is discussed and consideration is given to radioactive particles in the context of radiological protection.

Field effects studies in the Chernobyl Exclusion Zone: Lessons to be learnt

In the initial aftermath of the 1986 Chernobyl accident there were detrimental effects recorded on wildlife, including, mass mortality of pine trees close to the reactor, reduced pine seed production, reductions in soil invertebrate abundance and diversity and likely death of small mammals. More than 30 years after the Chernobyl accident there is no consensus on the longer-term impact of the chronic exposure to radiation on wildlife in what is now referred to as the Chernobyl Exclusion Zone. Reconciling this lack of consensus is one of the main challenges for radioecology. With the inclusion of environmental protection in, for instance, the recommendations of the International Commission on Radiological Protection (ICRP), we need to be able to incorporate knowledge of the potential effects of radiation on wildlife within the regulatory process (e.g. as a basis on which to define benchmark dose rates). In this paper, we use examples of reported effects on different wildlife groups inhabiting the Chernobyl Exclusion Zone (CEZ) as a framework to discuss potential reasons for the lack of consensus, consider important factors influencing dose rates organisms receive and make some recommendations on good practice.

ICRP Publication 136: Dose Coefficients for Non-human Biota Environmentally Exposed to Radiation

Abstract –

The diversity of non-human biota is a specific challenge when developing and applying dosimetric models for assessing exposures of flora and fauna from radioactive sources in the environment. Dosimetric models, adopted in Publication 108, provide dose coefficients (DCs) for a group of reference entities [Reference Animals and Plants (RAPs)]. The DCs can be used to evaluate doses and dose rates, and to compare the latter with derived consideration reference levels (DCRLs), which are bands of dose rate where some sort of detrimental effect in a particular RAP may be expected to occur following chronic, long-term radiation exposure, as outlined in Publication 124. These dosimetric models pragmatically assume simple body shapes with uniform composition and density, homogeneous internal contamination, limited sets of idealised sources of external exposure to ionising radiation for aquatic and terrestrial animals and plants, and truncated radioactive decay chains. This pragmatic methodology is further developed and systematically extended in this publication, which supersedes the DC values of Publication 108. Significant methodological changes since Publication 108 include: implementation of a new approach for external exposure of terrestrial animals with an extended set of environmental radioactive sources in soil and in air; considering an extended range of organisms and locations in contaminated terrain; transition to the contemporary radionuclide database of Publication 107; assessment-specific consideration of the contribution of radioactive progeny to DCs of parent radionuclides; and use of generalised allometric relationships in the estimation of biokinetic or metabolic parameter values. These methodological developments result in changes to previously published tables of DCs for RAPs, and revised values are provided in this publication. This publication is complemented by a new software tool, called ‘BiotaDC’, which enables the calculation of DCs for internal and external exposures of organisms with user-defined masses, shapes, and locations in the environment and for all radionuclides in Publication 107.

Implementation of the integrated approach in different types of exposure scenarios

The International Commission on Radiological Protection (ICRP) recognises three types of exposure situations: planned, existing, and emergency. In all three situations, the release of radionuclides into the natural environment leads to exposures of non-human biota, as well as the potential for exposures of the public. This paper describes how the key principles of the ICRP system of radiological protection apply to non-human biota and members of the public in each of these exposure situations. Current work in this area within ICRP Task Group 105 is highlighted. For example, how simplified numeric criteria may be used in planned exposure situations that are protective of both the public and non-human biota. In emergency exposure situations, the initial response will always be focused on human protection; however, understanding the potential impacts of radionuclide releases on non-human biota will likely become important in terms of communication as governments and the public seek to understand the exposures that are occurring. For existing exposure situations, there is a need to better understand the potential impacts of radionuclides on animals and plants, especially when deciding on protective actions. Understanding the comparative impacts from radiological, non-radiological, and physical aspects is often important in managing the remediation of legacy sites. Task Group 105 is making use of case studies of how exposure situations have been managed in the past to provide additional guidance and advice for the protection of non-human biota.

Protection of the environment in existing exposure situations

The International Commission on Radiological Protection (ICRP) described its approach to the protection of the environment and how it should be applied in Publication 124 The report expanded on the Commission's objectives for environmental protection, and how the Derived Consideration Reference Levels (DCRLs) apply within different exposure situations. DCRLs relate radiation effects to doses over and above their normal local background radiation levels, and consider different potential pathways of exposure for animals and plants. This paper will describe how the DCRLs may be used within existing exposure situations to better understand the potential impacts on animals and plants. In these circumstances, the Commission recommends that the aim be to reduce exposures to levels that are within the DCRL bands (or even below, depending upon the potential cost/benefits), but with full consideration of the radiological and non-radiological consequences of doing so. Using examples, this paper will demonstrate how this may be achieved in practice, bearing in mind the potential exposure of humans, animals and plants during and following any remediation attempted.

A new version of the ERICA tool to facilitate impact assessments of radioactivity on wild plants and animals

A new version of the ERICA Tool (version 1.2) was released in November 2014; this constitutes the first major update of the Tool since release in 2007. The key features of the update are presented in this article. Of particular note are new transfer databases extracted from an international compilation of concentration ratios (CRwo-media) and the modification of 'extrapolation' approaches used to select transfer data in cases where information is not available. Bayesian updating approaches have been used in some cases to draw on relevant information that would otherwise have been excluded in the process of deriving CRwo-media statistics. All of these efforts have in turn led to the requirement to update Environmental Media Concentration Limits (EMCLs) used in Tier 1 assessments. Some of the significant changes with regard to EMCLs are highlighted.

ICRP's approach to protection of the living environment under different exposure situations

The International Commission on Radiological Protection's (ICRP) system to protect the living components of the environment is designed to provide a broad and practical framework across all exposure situations. The objectives of ICRP are therefore also set in fairly broad terms, recognising that national and local environmental protection requirements may need to be set within them. The framework recognises the need to be able to demonstrate an adequate level of protection in relation to planned exposure situations, whilst also providing an ability to manage existing situations and accidents, as well as emergency situations, in a rational way. The objects of protection are always real biota in real exposure situations, and the scientific basis for their protection needs to be based on data originating from studies on the relationships between exposure and dose, dose and effects, and effects and consequences in real animals and plants. The framework that has been developed has therefore had to take such realities into account to make the optimum use of the data currently available, whilst being sufficiently flexible to accommodate new scientific information as it arises without having to alter the framework as a whole.

A method for estimating (41)Ar, (85)(,88)Kr and (131m,133)Xe doses to non-human biota

A method is presented for estimating (41)Ar, (85,88)Kr and (131m,133)Xe dose rates to terrestrial wildlife without having to resort to comparisons with analogue radionuclides. The approach can be used to calculate the dose rates arising from external exposures to given ambient air concentrations of these isotopes. Dose conversion coefficient (DCC) values for a range of representative organisms are calculated, using a Monte Carlo approach to generate absorbed fractions based on representing animals as reference ellipsoid geometries. Plume immersion is the main component of the total DCC. DCC values calculated for a human-sized organism are compared with human dose conversion factors from ICRP Publication 119, demonstrating the consistency of the biota approach with that for humans. An example of application is provided for hypothetical nuclear power plant atmospheric discharges with associated exposures to birds and insects. In this example, the dose rates appear to be dominated by (133)Xe and (88)Kr, respectively. The biota considered would be protected from the effects of noble gas radiation from a population protection perspective.

Transfer parameters for ICRP reference animals and plants collected from a forest ecosystem

The International Commission on Radiological Protection (ICRP) have suggested the identification of a series of terrestrial, marine and freshwater sites from which samples of each Reference animal and plant (RAP) could be systematically collected and analysed. We describe the first such study in which six of the eight terrestrial RAPs, and associated soil samples, were collected from a site located in a managed coniferous forestry plantation in north-west England. Adult life stages of species representing six of the terrestrial RAPs (Wild grass, Pine tree, Deer, Rat, Earthworm and Bee) were sampled and analysed to determine concentrations of 60 elements and gamma-emitting radionuclides. The resultant data have been used to derive concentration ratios (CR(wo-soil)) relating element/radionuclide concentrations in the RAPs to those in soil. This paper presents the first-reported transfer parameters for a number of the RAP-element combinations. Where possible, the derived CR(wo-soil) values are compared with the ICRPs-recommended values and any appreciable differences discussed.

ICRP Publication 124: Protection of the Environment under Different Exposure Situations

In this report, the Commission describes its framework for protection of the environment and how it should be applied within the Commission’s system of protection. The report expands upon its objectives in relation to protection of the environment, in so far as it relates to the protection of animals and plants (biota) in their natural environment, and how these can be met by the use of Reference Animals and Plants (RAPs); their Derived Consideration Reference Levels (DCRLs), which relate radiation effects to doses over and above their normal local background natural radiation levels; and different potential pathways of exposure. The report explains the different types of exposure situations to which its recommendations apply; the key principles that are relevant to protection of the environment; and hence how reference values based on the use of DCRLs can be used to inform on the appropriate level of effort relevant to different exposure situations. Further recommendations are made with regard to how the Commission’s recommendations can be implemented to satisfy different forms of environmental protection objectives, which may require the use of representative organisms specific to a site, and how these may be compared with the reference values. Additional information is also given with regard to, in particular, communication with other interested parties and stakeholders. Issues that may arise in relation to compliance are also discussed, and the final chapter discusses the overall implications of the Commission’s work in this area to date. Appendices A and B provide some numerical information relating to the RAPs. Annex C considers various existing types of environmental protection legislation currently in place in relation to large industrial sites and practices, and the various ways in which wildlife are protected from various threats arising from such sites.

Establishing a database of radionuclide transfer parameters for freshwater wildlife

Environmental assessments to evaluate potentials risks to humans and wildlife often involve modelling to predict contaminant exposure through key pathways. Such models require input of parameter values, including concentration ratios, to estimate contaminant concentrations in biota based on measurements or estimates of concentrations in environmental media, such as water. Due to the diversity of species and the range in physicochemical conditions in natural ecosystems, concentration ratios can vary by orders of magnitude, even within similar species. Therefore, to improve model input parameter values for application in aquatic systems, freshwater concentration ratios were collated or calculated from national grey literature, Russian language publications, and refereed papers. Collated data were then input into an international database that is being established by the International Atomic Energy Agency. The freshwater database enables entry of information for all radionuclides listed in ICRP (1983), in addition to the corresponding stable elements, and comprises a total of more than 16,500 concentration ratio (CRwo-water) values. Although data were available for all broad wildlife groups (with the exception of birds), data were sparse for many organism types. For example, zooplankton, crustaceans, insects and insect larvae, amphibians, and mammals, for which there were CRwo-water values for less than eight elements. Coverage was most comprehensive for fish, vascular plants, and molluscs. To our knowledge, the freshwater database that has now been established represents the most comprehensive set of CRwo-water values for freshwater species currently available for use in radiological environmental assessments.

An international database of radionuclide concentration ratios for wildlife: development and uses

A key element of most systems for assessing the impact of radionuclides on the environment is a means to estimate the transfer of radionuclides to organisms. To facilitate this, an international wildlife transfer database has been developed to provide an online, searchable compilation of transfer parameters in the form of equilibrium-based whole-organism to media concentration ratios. This paper describes the derivation of the wildlife transfer database, the key data sources it contains and highlights the applications for the data.

Evaluating summarised radionuclide concentration ratio datasets for wildlife

Concentration ratios (CR(wo-media)) are used in most radioecological models to predict whole-body radionuclide activity concentrations in wildlife from those in environmental media. This simplistic approach amalgamates the various factors influencing transfer within a single generic value and, as a result, comparisons of model predictions with site-specific measurements can vary by orders of magnitude. To improve model predictions, the development of 'condition-specific' CR(wo-media) values has been proposed (e.g. for a specific habitat). However, the underlying datasets for most CR(wo-media) value databases, such as the wildlife transfer database (WTD) developed within the IAEA EMRAS II programme, include summarised data. This presents challenges for the calculation and subsequent statistical evaluation of condition-specific CR(wo-media) values. A further complication is the common use of arithmetic summary statistics to summarise data in source references, even though CR(wo-media) values generally tend towards a lognormal distribution and should, therefore, be summarised using geometric statistics. In this paper, we propose a statistically-defensible and robust method for reconstructing underlying datasets to calculate condition-specific CR(wo-media) values from summarised data and deriving geometric summary statistics. This method is applied to terrestrial datasets from the WTD. Statistically significant differences in sub-category CR(wo-media) values (e.g. mammals categorised by feeding strategy) were identified, which may justify the use of these CR(wo-media) values for specific assessment contexts. However, biases and limitations within the underlying datasets of the WTD explain some of these differences. Given the uncertainty in the summarised CR(wo-media) values, we suggest that the CR(wo-media) approach to estimating transfer is used with caution above screening-level assessments.

Exploring methods to prioritise concentration ratios when estimating weighted absorbed dose rates to terrestrial Reference Animals and Plants

The ICRP and IAEA have recently reported Concentration Ratio values (CRwo-media--equilibrium radionuclide activity concentration in whole organism divided by that in media) for Reference Animals and Plants (RAPs) and a wide range of organism groups, respectively, based on a common online database. Given the large number of data gaps in both publications, there is a need to develop methods for identifying the relative importance of improving currently available CR(wo-media) values. A simple, transparent approach involving the derivation and comparison of predicted internal and external weighted absorbed dose rates for radionuclides considered by ICRP (2009) for terrestrial RAPs is presented. Using the approach of applying a reference value of CR(wo-soil) = 1 or using the maximum reported values where CR(wo-soil) >1, we provisionally identify terrestrial radionuclide RAP combinations which could be considered low priority, notably: Ca, Cr and Ni consistently; Mn for all RAPs except Deer and Pine Tree; and Tc for all RAPs but Wild Grass. Equally, we can systematically identify high priority elements and radioisotopes, which largely, but not exclusively, consist of alpha-emitters (especially isotopes of Ra and Th, but also consistently Am, Cf, Cm, Np, Pa, Po, Pu, U). The analysis highlights the importance of the radiation weighting factor default assumption of 10 for alpha-emitters in the ERICA Tool when comparing the magnitude of the internal dose and trying to identify high priority RAP-isotope combinations. If the unweighted Dose Conversion Coefficient (DCC) values are considered, those for alpha-emitters are often one order of magnitude higher than those due to some beta-gamma emitters for terrestrial RAPs, whereas with the radiation weighting factor applied they are two orders of magnitude higher.

The radium legacy: Contaminated land and the committed effective dose from the ingestion of radium contaminated materials

The manufacture and use of radium in the early to mid-20th century within industrial, medicinal and recreational products have resulted in a large number of contaminated sites across a number of countries with notable examples in the USA and Europe. These sites, represent a significant number of unregulated sources of potential radiological exposure that have collectively and hitherto not been well characterised. In 2007, the Radioactive Contaminated Land (RCL) Regulations came into force in the UK, providing the statutory guidance for regulators to classify and deal with RCL. Here we report on results derived from digestion experiments to estimate committed effective dose, a key aspect of the RCL Regulations, from the ingestion of radium contaminated sources that can be found in the environment. This case study includes particles, clinker and artefacts that arise from past military activities on a site that was once an airfield at Dalgety Bay on the Firth of Forth, UK. Since 2011 the number of radium contaminated finds has increased by one order of magnitude on the foreshore areas of Dalgety Bay. The increase in finds may in large part be attributed to a change in monitoring practice. A subsample of sixty sources was selected, on the basis of their activity and dimensions, and subjected to digestion in simulated stomach and lower intestine solutions. The study demonstrated that more radium-226 ((226)Ra) and lead-210 ((210)Pb; driven by Polonium solubility) are dissolved from sources in artificial 'stomach' solutions compared with 'lower intestine' solutions. The combined 'gut' solubility for (226)Ra and apparent (210)Pb varied from less than 1% to up to 35% ICRP 72 conversion factors were used to convert the activities measured in solution to committed effective dose. A little over 10% of the sources tested dissolved sufficient radioactivity to result in 100mSv committed effective dose to an infant. Using the solubility of 35% as a worst case, minimum source activities necessary to deliver 100mSv to the full age range of users of the foreshore were estimated. All the estimated activities have been detected and recovered through routine monitoring.

The IAEA handbook on radionuclide transfer to wildlife

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.

Observations of Fukushima fallout in Great Britain

Following the Fukushima accident in March 2011, grass samples were collected from 42 sites around Great Britain during April 2011. Iodine-131 was measurable in grass samples across the country with activity concentrations ranging from 10 to 55 Bq kg(-1) dry matter. Concentrations were similar to those reported in other European countries. Rainwater and some foodstuffs were also analysed from a limited number of sites. Of these, (131)I was only detectable in sheep's milk (c. 2 Bq kg(-1)). Caesium-134, which can be attributed to releases from the Fukushima reactors, was detectable in six of the grass samples (4-8 Bq kg(-1) dry matter); (137)Cs was detected in a larger number of grass samples although previous release sources (atmospheric weapons test and the 1986 Chernobyl and 1957 Windscale accidents) are likely to have contributed to this.

Exposure of burrowing mammals to 222Rn

Estimates of absorbed dose rates to wildlife from exposure to natural background radionuclides are required to put estimates of dose rates arising from regulated releases of radioactivity and proposed benchmarks into context. Recent review papers have estimated dose rates to wildlife from (40)K, and (238)U and (232)Th series radionuclides. However, only one study previous has considered the potential dose rates to burrowing animals from inhaled (222)Rn and its daughter products. In this paper we describe a study conducted at seven sites in northwest England. Passive track etch detectors were used to measure the (222)Rn concentrations in artificial burrows over a period of approximately one year. Results suggest that absorbed dose rates to burrowing mammals as a consequence of exposure to (222)Rn are likely to be at least an order of magnitude higher than those suggested in previous evaluations of natural background exposure rates which had omitted this radionuclide and exposure pathway. Dose rates in some areas of Great Britain will be considerably in excess of incremental no-effects benchmark dose rates suggested for use as screening levels. Such advised benchmark dose rates need to be better put into context with background dose rates, including exposure to (222)Rn, to ensure credibility; although the context will be determined by the purpose of the benchmark and the assessment level.

Allometric methodology for the assessment of radon exposures to terrestrial wildlife

A practical approach to calculate (222)Rn daughter dose rates to terrestrial wildlife is presented. The method scales allometrically the relevant parameters for respiration in different species of wildlife, allowing inter-species calculation of the dose per unit radon concentration in air as simple base-and-exponent power functions of the mass. For plants, passive gas exchange through the leaf surface is assumed, also leading to specific power relationships with mass. The model generates conservative predictions in which the main contributor to the dose rate of target tissues of the respiratory system is from α radiation arising from (222)Rn daughters. Tabulated (222)Rn DPURn values are given for 69 species used by the England & Wales Environment Agency for habitats assessments. The approach is then applied to assess the authorised discharges of (222)Rn from sites in England, demonstrating that, from a whole-body dose perspective, the biota considered are protected from effects at the population level.

Effects of chronic exposure in populations of Koeleria gracilis Pers. from the Semipalatinsk nuclear test site, Kazakhstan

Morphological and cytogenetic abnormalities were examined in crested hairgrass (Koeleria gracilis Pers.) populations inhabiting the Semipalatinsk nuclear test site (STS), Kazakhstan. Sampling of biological material and soil was carried out during 3 years (2005-2007) at 4 sites within the STS. Activity concentrations of 10 radionuclides and 8 heavy metals content in soils were measured. Doses absorbed by plants were estimated and varied, depending on the plot, from 4 up to 265 mGy/y. The frequency of cytogenetic alterations in apical meristem of germinated seeds from the highly contaminated plot significantly exceeded the level observed at other plots with lower levels of radioactive contamination during all three years of the study. A significant excess of chromosome aberrations, typical for radiation exposure, as well as a dependence of the frequency of these types of mutations on dose absorbed by plants were revealed. The results indicate the role radioactive contamination plays in the occurrence of cytogenetic effects. However, no radiation-dependent morphological alterations were detected in the progeny of the exposed populations. Given that the crested hairgrass populations have occupied the radioactively contaminated plots for some 50 years, adaptation to the radiation stress was not evident. The findings obtained were in agreement with the benchmark values proposed in the FASSET and ERICA projects to restrict radiation impacts on biota.

Model-derived dose rates per unit concentration of radon in air in a generic plant geometry

A model for the derivation of dose rates per unit radon concentration in plants was developed in line with the activities of a Task Group of the International Commission on Radiological Protection (ICRP), aimed at developing more realistic dosimetry for non-human biota. The model considers interception of the unattached and attached fractions of the airborne radon daughters by plant stomata, diffusion of radon gas through stomata, permeation through the plant's epidermis and translocation of deposited activity to plant interior. The endpoint of the model is the derivation of dose conversion coefficients relative to radon gas concentration at ground level. The model predicts that the main contributor to dose is deposition of (214)Po α-activity on the plant surface and that diffusion of radon daughters through the stomata is of relatively minor importance; hence, daily variations have a small effect on total dose.

The estimation of absorbed dose rates for non-human biota: an extended intercomparison

An exercise to compare 10 approaches for the calculation of unweighted whole-body absorbed dose rates was conducted for 74 radionuclides and five of the ICRP's Reference Animals and Plants, or RAPs (duck, frog, flatfish egg, rat and elongated earthworm), selected for this exercise to cover a range of body sizes, dimensions and exposure scenarios. Results were analysed using a non-parametric method requiring no specific hypotheses about the statistical distribution of data. The obtained unweighted absorbed dose rates for internal exposure compare well between the different approaches, with 70% of the results falling within a range of variation of ±20%. The variation is greater for external exposure, although 90% of the estimates are within an order of magnitude of one another. There are some discernible patterns where specific models over- or under-predicted. These are explained based on the methodological differences including number of daughter products included in the calculation of dose rate for a parent nuclide; source-target geometry; databases for discrete energy and yield of radionuclides; rounding errors in integration algorithms; and intrinsic differences in calculation methods. For certain radionuclides, these factors combine to generate systematic variations between approaches. Overall, the technique chosen to interpret the data enabled methodological differences in dosimetry calculations to be quantified and compared, allowing the identification of common issues between different approaches and providing greater assurance on the fundamental dose conversion coefficient approaches used in available models for assessing radiological effects to biota.

An international model validation exercise on radionuclide transfer and doses to freshwater biota

Under the International Atomic Energy Agency (IAEA)'s EMRAS (Environmental Modelling for Radiation Safety) programme, activity concentrations of (60)Co, (90)Sr, (137)Cs and (3)H in Perch Lake at Atomic Energy of Canada Limited's Chalk River Laboratories site were predicted, in freshwater primary producers, invertebrates, fishes, herpetofauna and mammals using eleven modelling approaches. Comparison of predicted radionuclide concentrations in the different species types with measured values highlighted a number of areas where additional work and understanding is required to improve the predictions of radionuclide transfer. For some species, the differences could be explained by ecological factors such as trophic level or the influence of stable analogues. Model predictions were relatively poor for mammalian species and herpetofauna compared with measured values, partly due to a lack of relevant data. In addition, concentration ratios are sometimes under-predicted when derived from experiments performed under controlled laboratory conditions representative of conditions in other water bodies.

Assessment of risk to wildlife from ionising radiation: can initial screening tiers be used with a high level of confidence?

A number of models are being used to assess the potential environmental impact of releases of radioactivity. These often use a tiered assessment structure whose first tier is designed to be highly conservative and simple to use. An aim of using this initial tier is to identify sites of negligible concern and to remove them from further consideration with a high degree of confidence. In this paper we compare the screening assessment outputs of three freely available models. The outputs of these models varied considerably in terms of estimated risk quotient (RQ) and the radionuclide-organism combinations identified as being the most limiting. A number of factors are identified as contributing to this variability: values of transfer parameters (concentration ratios and K(d)) used; organisms considered; different input options and how these are utilised in the assessment; assumptions as regards secular equilibrium; geometries and exposure scenarios. This large variation in RQ values between models means that the level of confidence required by users is not achieved. We recommend that the factors contributing to the variation in screening assessments be subjected to further investigation so that they can be more fully understood and assessors (and those reviewing assessment outputs) can better justify and evaluate the results obtained.

Protection of the environment from ionising radiation in a regulatory context--an overview of the PROTECT coordinated action project

The outcome of the PROTECT project (Protection of the Environment from Ionising Radiation in a Regulatory Context) is summarised, focusing on the protection goal and derivation of dose rates which may detrimentally affect wildlife populations. To carry out an impact assessment for radioactive substances, the estimated dose rates produced by assessment tools need to be compared with some form of criteria to judge the level of risk. To do this, appropriate protection goals need to be defined and associated predefined dose rate values, or benchmarks, derived and agreed upon. Previous approaches used to estimate dose rates at which there may be observable changes in populations or individuals are described and discussed, as are more recent derivations of screening benchmarks for use in regulatory frameworks. We have adopted guidance and procedures used for assessment and regulation of other chemical stressors to derive benchmarks. On the basis of consultation with many relevant experts, PROTECT has derived a benchmark screening dose rate, using data on largely reproductive effects to derive species sensitivity distributions, of 10 microGy h(-1) which can be used to identify situations which are below regulatory concern with a high degree of confidence.

Predicting the radiation exposure of terrestrial wildlife in the Chernobyl exclusion zone: an international comparison of approaches

There is now general acknowledgement that there is a requirement to demonstrate that species other than humans are protected from anthropogenic releases of radioactivity. A number of approaches have been developed for estimating the exposure of wildlife and some of these are being used to conduct regulatory assessments. There is a requirement to compare the outputs of such approaches against available data sets to ensure that they are robust and fit for purpose. In this paper we describe the application of seven approaches for predicting the whole-body ((90)Sr, (137)Cs, (241)Am and Pu isotope) activity concentrations and absorbed dose rates for a range of terrestrial species within the Chernobyl exclusion zone. Predictions are compared against available measurement data, including estimates of external dose rate recorded by thermoluminescent dosimeters attached to rodent species. Potential reasons for differences between predictions between the various approaches and the available data are explored.

Considerations for the integration of human and wildlife radiological assessments

A number of tools and approaches have been developed recently to allow assessments of the environmental impact of radiation on wildlife to be undertaken. The International Commission on Radiological Protection (ICRP) has stated an intention to provide a more inclusive protection framework for humans and the environment. Using scenarios, which are loosely based on real or predicted discharge data, we investigate how radiological assessments of humans and wildlife can be integrated with special consideration given to the recent outputs of the ICRP. We highlight how assumptions about the location of the exposed population of humans and wildlife, and the selection of appropriate benchmarks for determining potential risks can influence the outcome of the assessments. A number of issues associated with the transfer component and numeric benchmarks were identified, which need to be addressed in order to fully integrate the assessment approaches. A particular issue was the lack of comparable benchmark values for humans and wildlife. In part this may be addressed via the ICRP's recommended derived consideration reference levels for their 12 Reference Animals and Plants.

A multi-criteria weight of evidence approach for deriving ecological benchmarks for radioactive substances

Dose rate benchmarks are required in the tiered approaches used to screen out benign exposure scenarios in radiological ecological risk assessment. Such screening benchmarks, namely the predicted no-effect dose rates (PNEDR), have been derived by applying, as far as possible, the European guidance developed for chemicals. To derive the ecosystem level (or generic) PNEDR, radiotoxicity EDR(10) data (dose rates giving a 10% effect in comparison with the control) were used to fit a species sensitivity distribution (SSD) and estimate the HDR(5) (the hazardous dose rate affecting 5% of species with a 10% effect). Then, a multi-criteria approach was developed to justify using an assessment factor (AF) to apply to the HDR(5) for estimating a PNEDR value. Several different statistical data treatments were considered which all gave reasonably similar results. The suggested generic screening value of 10 microGy h(-1) (incremental dose rate) was derived using the lowest available EDR(10) value per species, an unweighted SSD, and an AF of 2 applied to the estimated HDR(5). Consideration was also given to deriving screening benchmark values for organism groups but this was not thought to be currently appropriate due to few relevant data being currently available.

Exposure of birds to radionuclides and other contaminants in Special Protection Areas (SPAs) in North-West England

There has been a decline in the population of some bird species at Morecambe Bay and the Solway Firth Special Protected Areas in North-West England during the last fifty years. It was suggested that the declines were caused, in part, by contaminants in the food and environment, primarily from the radioactive effluent discharge from the Sellafield Ltd nuclear fuel reprocessing plant in Cumbria. This study analysed bird feathers and tissues, vegetation and sediment for radionuclides, metals and persistent organic compounds. The non-radionuclide results were all low compared to relevant action limits. The ERICA model was used with field data to estimate the radiological dose to birds from exposure to (137)Cs and (241)Am with results between 1.26 to 3.83 microGy h(-1), below the ERICA screening level of 10 microGy h(-1) and within the IAEA 40 microGy h(-1) guideline value below which potential adverse impacts on biota are unlikely. The study showed no link between bird population decline and anthropogenic discharges to the SPAs.

ICRP Publication 114. Environmental protection: transfer parameters for reference animals and plants

In Publication 103 (ICRP, 2007), the Commission included a section on the protection of the environment, and indicated that it would be further developing its approach to this difficult subject by way of a set of Reference Animals and Plants (RAPs) as the basis for relating exposure to dose, and dose to radiation effects, for different types of animals and plants. Subsequently, a set of 12 RAPs has been described in some detail (ICRP, 2008), particularly with regard to estimation of the doses received by them, at a whole-body level, in relation to internal and external radionuclide concentrations; and what is known about the effects of radiation on such types of animals and plants. A set of dose conversion factors for all of the RAPs has been derived, and the resultant dose rates can be compared with evaluations of the effects of dose rates using derived consideration reference levels (DCRLs). Each DCRL constitutes a band of dose rates for each RAP within which there is likely to be some chance of the occurrence of deleterious effects. Site-specific data on Representative Organisms (i.e. organisms of specific interest for an assessment) can then be compared with such values and used as a basis for decision making. It is intended that the Commission's approach to protection of the environment be applied to all exposure situations. In some situations, the relevant radionuclide concentrations can be measured directly, but this is not always possible or feasible. In such cases, modelling techniques are used to estimate the radionuclide concentrations. This report is an initial step in addressing the needs of such modelling techniques. After briefly reviewing the basic factors relating to the accumulation of radionuclides by different types of biota, in different habitats, and at different stages in the life cycle, this report focuses on the approaches used to model the transfer of radionuclides through the environment. It concludes that equilibrium concentration ratios (CRs) are most commonly used to model such transfers, and that they currently offer the most comprehensive data coverage. The report also reviews the methods used to derive CRs, and describes a means of summarising statistical information from empirical data sets. Emphasis has been placed on using data from field studies, although some data from laboratory experiments have been included for some RAPs. There are, inevitably, many data gaps for each RAP, and other data have been used to help fill these gaps. CRs specific to each RAP were extracted from a larger database, structured in terms of generic wildlife groups. In cases where data were lacking, values from taxonomically-related organisms were used to derive suitable surrogate values. The full set of rules which have been applied for filling gaps in RAP-specific CRs is described. Statistical summaries of the data sets are provided, and CR values for 39 elements and 12 RAP combinations are given. The data coverage, reliance on derived values, and applicability of the CR approach for each of the RAPs is discussed. Finally, some consideration is given to approaches where RAPs and their life stages could be measured for the elements of interest under more rigorously controlled conditions to help fill the current data gaps.

Radionuclide transfer to invertebrates and small mammals in a coastal sand dune ecosystem

International intercomparisons of models to assess the impact of ionising radiation on wildlife have identified radionuclide transfer assumptions as a significant source of uncertainty in the modelling process. There is a need to improve the underpinning data sets on radionuclide transfer to reduce this uncertainty, especially for poorly-studied ecosystems such as coastal sand dunes. This paper presents the results of the first published study of radionuclide transfer to invertebrates and small mammals in a coastal sand dune ecosystem. Activity concentrations of (137)Cs, (238)Pu, (239+240)Pu and (241)Am are reported for detritivorous, herbivorous, carnivorous and omnivorous biota. Differences in activity concentrations measured in the sand dune biota are related to the trophic level of the organisms and the influence of sea-to-land transfer is apparent in the food chain transfer observed at the site. There are notable differences in the concentration ratios (CRs) calculated for the sand dune biota compared to other terrestrial ecosystems, especially for the small mammals which have CRs that are two orders of magnitude lower than the generic terrestrial ecosystem CRs published by the recent EC EURATOM ERICA project. The lower CRs at the sand dunes may be due to the influence of other cations from the marine environment (e.g. K and Na) on the net radionuclide transfer observed, but further research is required to test this hypothesis.

Inter-comparison of models to estimate radionuclide activity concentrations in non-human biota

A number of models have recently been, or are currently being, developed to enable the assessment of radiation doses from ionising radiation to non-human species. A key component of these models is the ability to predict whole-organism activity concentrations in a wide range of wildlife. In this paper, we compare the whole-organism activity concentrations predicted by eight models participating within the IAEA Environmental Modelling for Radiation Safety programme for a range of radionuclides to terrestrial and freshwater organisms. In many instances, there was considerable variation, ranging over orders of magnitude, between the predictions of the different models. Reasons for this variability (including methodology, data source and data availability) are identified and discussed. The active participation of groups responsible for the development of key models within this exercise is a useful step forward in providing the transparency in methodology and data provenance required for models which are either currently being used for regulatory purposes or which may be used in the future. The work reported in this paper, and supported by other findings, demonstrates that the largest contribution to variability between model predictions is the parameterisation of their transfer components. There is a clear need to focus efforts and provide authoritative compilations of those data which are available.

Issues and practices in the use of effects data from FREDERICA in the ERICA Integrated Approach

The ERICA Integrated Approach requires that a risk assessment screening dose rate is defined for the risk characterisation within Tiers 1 and 2. At Tier 3, no numerical screening dose rate is used, and the risk characterisation is driven by methods that can evaluate the possible effects of ionising radiation on reproduction, mortality and morbidity. Species sensitivity distribution has been used to derive the ERICA risk assessment predicted no-effect dose rate (PNEDR). The method used was based on the mathematical processing of data from FRED (FASSET radiation effects database merged with the EPIC database to form FREDERICA) and resulted in a PNEDR of 10 microGy/h. This rate was assumed to ascribe sufficient protection of all ecosystems from detrimental effects on structure and function under chronic exposure. The value was weighed against a number of points of comparison: (i) PNEDR values obtained by application of the safety factor method, (ii) background levels, (iii) dose rates triggering effects on radioactively contaminated sites and (iv) former guidelines from literature reviews. In Tier 3, the effects analysis must be driven by the problem formulation and is thus highly case specific. Instead of specific recommendations on numeric values, guidance on the sorts of methods that may be applied for refined effect analysis is provided and illustrated.

Derivation of transfer parameters for use within the ERICA Tool and the default concentration ratios for terrestrial biota

An ability to predict radionuclide activity concentrations in biota is a requirement of any method assessing the exposure of biota to ionising radiation. Within the ERICA Tool fresh weight whole-body activity concentrations in organisms are estimated using concentration ratios (the ratio of the activity concentration in the organism to the activity concentration in an environmental media). This paper describes the methodology used to derive the default terrestrial ecosystem concentration ratio database available within the ERICA Tool and provides details of the provenance of each value for terrestrial reference organisms. As the ERICA Tool considers 13 terrestrial reference organisms and the radioisotopes of 31 elements, a total of 403 concentration ratios were required for terrestrial reference organisms. Of these, 129 could be derived from literature review. The approaches taken for selecting the remaining values are described. These included, for example, assuming values for similar reference organisms and/or biogeochemically similar elements, and various simple modelling approaches.

Background exposure rates of terrestrial wildlife in England and Wales

It has been suggested that, when assessing radiation impacts on non-human biota, estimated dose rates due to anthropogenically released radionuclides should be put in context by comparison to dose rates from natural background radiation. In order to make these comparisons, we need data on the activity concentrations of naturally occurring radionuclides in environmental media and organisms of interest. This paper presents the results of a study to determine the exposure of terrestrial organisms in England and Wales to naturally occurring radionuclides, specifically (40)K, (238)U series and (232)Th series radionuclides. Whole-body activity concentrations for the reference animals and plants (RAPs) as proposed by the ICRP have been collated from literature review, data archives and a targeted sampling campaign. Data specifically for the proposed RAP are sparse. Soil activity concentrations have been derived from an extensive geochemical survey of the UK. Unweighted and weighted absorbed dose rates were estimated using the ERICA Tool. Mean total weighted whole-body absorbed dose rates estimated for the selected terrestrial organisms was in the range 6.9 x 10(-2) to 6.1 x 10(-1) microGy h(-1).

Addressing uncertainties in the ERICA Integrated Approach

Like any complex environmental problem, ecological risk assessment of the impacts of ionising radiation is confounded by uncertainty. At all stages, from problem formulation through to risk characterisation, the assessment is dependent on models, scenarios, assumptions and extrapolations. These include technical uncertainties related to the data used, conceptual uncertainties associated with models and scenarios, as well as social uncertainties such as economic impacts, the interpretation of legislation, and the acceptability of the assessment results to stakeholders. The ERICA Integrated Approach has been developed to allow an assessment of the risks of ionising radiation, and includes a number of methods that are intended to make the uncertainties and assumptions inherent in the assessment more transparent to users and stakeholders. Throughout its development, ERICA has recommended that assessors deal openly with the deeper dimensions of uncertainty and acknowledge that uncertainty is intrinsic to complex systems. Since the tool is based on a tiered approach, the approaches to dealing with uncertainty vary between the tiers, ranging from a simple, but highly conservative screening to a full probabilistic risk assessment including sensitivity analysis. This paper gives on overview of types of uncertainty that are manifest in ecological risk assessment and the ERICA Integrated Approach to dealing with some of these uncertainties.

The development and purpose of the FREDERICA radiation effects database

Any system for assessing the impact of a contaminant on the environment requires an analysis of the possible effects on the organisms and ecosystems concerned. To facilitate this, the FREDERICA radiation effects database has been developed to provide an online search of the known effects of ionising radiation on non-human species, taken from papers in the scientific peer reviewed literature. The FREDERICA radiation effects database has been produced by merging the work done on radiation effects under two European funded projects (FASSET and EPIC) and making the database available online. This paper highlights applications for the database, gaps in the available data and explains the use of quality scores to help users of the database determine which papers may benefit their research in terms of techniques and reproducibility.

Decision-making in environmental radiation protection: using the ERICA Integrated Approach

The ERICA Integrated Approach and its associated tool and databases provide a method by which the likely impact of radioactive discharges on the environment can be evaluated, see Fig. 1. The various factors, which should be taken into account when making decisions both during and after an assessment has been made, are discussed for each stage in the assessment process for a hypothetical case study. The assessment will demonstrate the issues associated with the decision-making process at Tiers 1 and 2 within the ERICA Tool and how they may vary. The case study, set in England, evaluates the environmental impact of radioactive substances released under authorisation in response primarily to conservation legislation, because of the need to demonstrate that no adverse impacts will occur on Natura 2000 sites as a result of the release of an authorised substance.

The ERICA Tool

The ERICA Tool is a computerised, flexible software system that has a structure based upon the ERICA Integrated Approach to assessing the radiological risk to biota. The Tool guides the user through the assessment process, recording information and decisions and allowing the necessary calculations to be performed to estimate risks to selected animals and plants. Tier 1 assessments are media concentration based and use pre-calculated environmental media concentration limits to estimate risk quotients. Tier 2 calculates dose rates but allows the user to examine and edit most of the parameters used in the calculation including concentration ratios, distribution coefficients, percentage dry weight soil or sediment, dose conversion coefficients, radiation weighting factors and occupancy factors. Tier 3 offers the same flexibility as Tier 2 but allows the option to run the assessment probabilistically if the underling parameter probability distribution functions are defined. Results from the Tool can be put into context using incorporated data on dose-effects relationships and background dose rates.

Application of the ERICA Integrated Approach to the Drigg coastal sand dunes

The EC-funded project 'Environmental Risks from Ionising Contaminants: Assessment and Management' (ERICA) developed an 'Integrated Approach' for assessing the impact of ionising radiation on ecosystems. This paper presents the application of the ERICA Integrated Approach, supported by a software programme (the ERICA Tool) and guidance documentation, to an assessment of the Drigg coastal sand dunes (Cumbria, UK). Targeted sampling provided site-specific data for sand dune biota, including amphibians and reptiles. Radionuclides reported included (90)Sr, (99)Tc, (137)Cs, (238)Pu, (239+240)Pu and (241)Am. Site-specific data were compared to predictions derived using the ERICA Tool. Some under- and over-predictions of biota activity concentrations were identified but can be explained by the specific ecological characteristics and contamination mechanism of the dunes. Overall, the results indicated no significant impact of ionising radiation on the sand dune biota and the Integrated Approach was found to be a flexible and effective means of conducting a radiation impact assessment.

Estimating the exposure of small mammals at three sites within the Chernobyl exclusion zone--a test application of the ERICA Tool

An essential step in the development of any modelling tool is the validation of its predictions. This paper describes a study conducted within the Chernobyl exclusion zone to acquire data to conduct an independent test of the predictions of the ERICA Tool which is designed for use in assessments of radiological risk to the environment. Small mammals were repeatedly trapped at three woodland sites between early July and mid-August 2005. Thermoluminescent dosimeters mounted on collars were fitted to Apodemus flavicollis, Clethrionomys glareolus and Microtus spp. to provide measurements of external dose rate. A total of 85 TLDs were recovered. All animals from which TLDs were recovered were live-monitored to determine (90)Sr and (137)Cs whole-body activity concentrations. A limited number of animals were also analysed to determine (239,240)Pu activity concentrations. Measurements of whole-body activity concentrations and dose rates recorded by the TLDs were compared to predictions of the ERICA-Tool. The predicted (90)Sr and (137)Cs mean activity concentrations were within an order of magnitude of the observed data means. Whilst there was some variation between sites in the agreement between measurements and predictions this was consistent with what would be expected from the differences in soil types at the sites. Given the uncertainties of conducting a study such as this, the agreement observed between the TLD results and the predicted external dose rates gives confidence to the predictions of the ERICA Tool.

Inter-comparison of absorbed dose rates for non-human biota

A number of approaches have been proposed to estimate the exposure of non-human biota to ionizing radiation. This paper reports an inter-comparison of the unweighted absorbed dose rates for the whole organism (compared as dose conversion coefficients, or DCCs) for both internal and external exposure, estimated by 11 of these approaches for selected organisms from the Reference Animals and Plants geometries as proposed by the International Commission on Radiological Protection. Inter-comparison results indicate that DCCs for internal exposure compare well between the different approaches, whereas variation is greater for external exposure DCCs. Where variation among internal DCCs is greatest, it is generally due to different daughter products being included in the DCC of the parent. In the case of external exposures, particularly to low-energy beta-emitters, variations are most likely to be due to different media densities being assumed. On a radionuclide-by-radionuclide basis, the different approaches tend to compare least favourably for (3)H, (14)C and the alpha-emitters. This is consistent with models with different source/target geometry assumptions showing maximum variability in output for the types of radiation having the lowest range across matter. The intercomparison demonstrated that all participating approaches to biota dose calculation are reasonably comparable, despite a range of different assumptions being made.

Seasonal variations in activity concentrations of 99Tc and 137Cs in the edible meat fraction of crabs and lobsters from the central Irish Sea

Discharges of most radionuclides into the Irish Sea from the BNFL site at Sellafield have decreased over the past 20 years or so. For a few radionuclides, however, discharges have peaked more recently. Notably, operation of the Enhanced Actinide Removal Plant (EARP) since 1994 has led to an increase in discharges of (99)Tc, as a result of the treatment of previously stored waste, with consequent increases in (99)Tc activity concentrations in a number of marine species, particularly in crustaceans such as lobsters. Previous research has considered the significance of factors such as sex and body weight on radionuclide concentrations. The current project set out to investigate whether seasonal variations in radionuclide concentrations in crabs and lobsters occur, with particular emphasis on the dynamics of (99)Tc and (137)Cs. Organisms were obtained from a site off the Isle of Man, where radionuclide concentrations were measurable but the site was sufficiently distant from Sellafield that the radionuclides were well mixed in the water column and not likely to be influenced by the pulsed nature of discharges of (99)Tc. Crab and lobster samples were collected monthly, between February 2000 and February 2001. Fifteen or 16 individuals (evenly split as male and female) of each species were collected on each occasion. Seawater samples were also collected over the 12-month period. Activity concentrations of (99)Tc in the edible meat fraction (both brown and white meat) ranged from 0.23 to 2.46 Bq kg(-1) (fresh weight (fw)) in crabs and 124 to 216 Bq kg(-1) (fw) in lobsters, with no observed seasonal variations. Activity concentrations of (137)Cs in both crab and lobster were lower, ranging from <0.16 to 0.85 Bq kg(-1) for crab meat (fw) and <0.3 to 3.3 Bq kg(-1) for lobster meat (fw). A statistically significant increase in activity concentrations of (137)Cs in the meat was observed in the summer months for both crab and lobster. The cause has not been investigated but may be related to the laying down of energy reserves during the active feeding period over the summer. At all times, uptake of (99)Tc is higher in the brown meat fraction of both crabs and lobsters, whilst (137)Cs is more uniformly distributed. These results are used to discuss the implications for sampling and monitoring programmes.