Dynamic model for the assessment of radiological exposure to marine biota

Impact of medical radionuclide discharges on people and the environment

We present a novel methodology to dynamically calculate dose rates to people and wildlife from hospital-released radionuclides reaching the environment through water treatment plants (WTPs), using the biokinetic model D-DAT for aquatic wildlife, applied to 18F, 123I, 131I, 153Sm, 99mTc and 201Tl. We have also developed a method to calculate doses to WTP workers and to farmers from agricultural practices. This proof-of-concept study simulates a generic source term of radionuclide levels in the Belgian Molse Nete River during the year 2018, chosen because the river flow was very low during that year, which constitutes a very conservative, bounding case. The dose rates to wildlife calculated for this hypothetical scenario under conservative assumptions, are well below the ERICA predicted no effects dose rate to wildlife of 10 μGy h-1. Human exposures are also very low, in most cases not exceeding 10 μSv y-1. This work identifies important data gaps and areas of uncertainty in the assessment of radiopharmaceutical effluents. The study, which is part of the EC project SINFONIA, paves the way for a dynamic screening assessment methodology able to perform consistently assessments of the impact of radiopharmaceuticals on people and wildlife. This is particularly relevant since discharges of radiopharmaceuticals in rivers are on the increase and it is necessary to explicitly demonstrate that people and the environment are adequately protected.

Comparison of methods for the radiological impact assessment of aquatic releases to the waters in the low countries

Accurate assessment of the radiological impact of liquid discharges on the marine environment is challenging despite all developments in recent years. The lack of consensus on this type of assessment manifests itself even stronger when transborder issues are expected, such as in the Low Countries. Belgium and the Netherlands operate nuclear power plants with discharges in the shared estuary of the Western Scheldt, therefore if there are safety concerns, information on both sides of the border must be coherent. This work provides a comparison of two computational methods used for assessment of aquatic releases in the Western Scheldt estuary and the adjacent North Sea.The work demonstrates a fair degree of consistency in modelling the uptake and fate of key anthropogenic radionuclides. Nevertheless, there are also considerable differences found in sediment and sea species with concentrations ranging by over two orders of magnitude in some cases. These explainable differences are methodological in nature, occurring in codes that underwent extensive validation during development. Therefore, the outcomes of this work clearly demonstrate the need to produce explicit guidance that is specifically tailored to the (inter)national water system of concern. This should not be limited to releases from nuclear power plants, but also include other nuclear applications. For all these reasons, more intensive collaboration and model harmonisation across borders is essential, signalling the direction for future investigations.

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.

Concentration factors and biological half-lives for the dynamic modelling of radionuclide transfers to marine biota in the English Channel

The biokinetics of radionuclide transfers to biota in the marine environment can be modelled using two parameters, specific to both each element/radionuclide and biota. The Concentration Factor (CF) reflects the ratio between the activity concentrations in the biota and the surrounding seawater in steady state. The biological half-life (tb_1/2) characterizes depuration kinetics for the radionuclide from the biota. While recommended CF values can be found in the literature, no guidelines actually exist for tb_1/2 values. We used available time-series activity concentration measurements in biota in the English Channel, where controlled amounts of liquid radioactive waste are discharged by the ORANO La Hague reprocessing plant. We calculated the corresponding time-series activity concentrations in seawater for each biota dataset using an extensively-validated hydrodynamic model. We derived the values of CF and tb_1/2 from seawater and biota data, to model radionuclide transfers between the two compartments. To assess the performance of the model, we analyzed the residual between observed and calculated levels in the biota. Datasets for macroalgae, mollusks, crustaceans and fish yielded parameters (CF, tb_1/2) for H-3 (as body water and as organically bound tritium), C-14, Sb-125, Cs-137, I-129, Mn-54, Co-60, Zn-65 and Ru-106. After discussing the results and qualifying the model's reliability, we proposed recommendations for CF and tb_1/2 for the purposes of the operational modelling of radionuclide transfers to biota in the marine environment.

Using a chain of models to predict health and environmental impacts in Norway from a hypothetical nuclear accident at the Sellafield site

When a nuclear accident occurs, decision makers in the affected country/countries would need to act promptly to protect people, the environment and societal interests from harmful impacts of radioactive fallout. The decisions are usually based on a combination of model prognoses, measurements, and expert judgements within in an emergency decision support system (DSS). Large scale nuclear accidents would need predictive models for the atmospheric, terrestrial, freshwater, and marine ecosystems, for the connections between these in terms of radionuclide fluxes, and for the various exposure pathways to both humans and biota. Our study showed that eight different models and DSS modules could be linked to assess the total human and environmental consequences in Norway from a hypothetical nuclear accident, here chosen to be the Sellafield nuclear reprocessing plant. Activity concentrations and dose rates from ¹³⁷Cs for both humans and the environment via various exposure routes were successfully modelled. The study showed that a release of 1% of the total inventory of ¹³⁷Cs in the Highly Active Liquor Tanks at Sellafield Ltd is predicted to severely impact humans and the environment in Norway if strong winds are blowing towards the country at the time of an accidental atmospheric release. Furthermore, since the models did not have built-in uncertainty ranges when this Sellafield study was performed, investigations were conducted to identify the key factors contributing to uncertainty in various models and prioritise the ones to focus on in future research.

Fukushima 137Cs releases dispersion modelling over the Pacific Ocean. Comparisons of models with water, sediment and biota data

A number of marine radionuclide dispersion models (both Eulerian and Lagrangian) were applied to simulate ¹³⁷Cs releases from Fukushima Daiichi nuclear power plant accident in 2011 over the Pacific at oceanic scale. Simulations extended over two years and both direct releases into the ocean and deposition of atmospheric releases on the ocean surface were considered. Dispersion models included an embedded biological uptake model (BUM). Three types of BUMs were used: equilibrium, dynamic and allometric. Model results were compared with ¹³⁷Cs measurements in water (surface, intermediate and deep layers), sediment and biota (zooplankton, non-piscivorous and piscivorous fish). A reasonable agreement in model/model and model/data comparisons was obtained.

Exploring taxonomic and phylogenetic relationships to predict radiocaesium transfer to marine biota

One potentially useful approach to fill data gaps for concentration ratios, CRs, is based upon the hypothesis that an underlying taxonomic and/or phylogenetic relationship exists for radionuclide transfer. The objective of this study was to explore whether these relationships could be used to explain variation in the transfer of radiocaesium to a wide range of marine organisms. CR data for ¹³⁷Cs were classified in relation to taxonomic family, order, class and phylum. A Residual Maximum Likelihood (REML) mixed-model regression modelling approach was adopted. The existence of any patterns were then explored using phylogenetic trees constructed with mitochondrial COI gene sequences from various biota groups and mapping the REML residual means onto these trees. A comparison of the predictions made using REML with blind datasets allowed the efficacy of the procedure to be tested. The only significant correlation between predicted and measured activity concentrations was revealed at the taxonomic level of order when comparing REML analysis output with data from the Barents Sea Region. For this single case a correlation 0.80 (Spearman rank) was derived which was significant at the 0.01 level (1-tailed test) although this was not the case once a (Bonferroni) correction was applied. The application of the REML approach to marine datasets has met with limited success, and the phylogenetic trees illustrate complications of using predictions based on values from different levels of taxonomic organization, where predicted values for the order level can mask the values at lower taxonomic levels. Any influence of taxonomy and phylogeny on transfer is not immediately conspicuous and categorizing marine organisms in this way is limited in providing a potentially robust prognostic extrapolation tool. Other factors may plausibly affect transfer to a much greater degree in marine systems, such as quite diverse life histories and different diets, which may confound any phylogenetic pattern.

ALLIANCE perspectives on integration of humans and the environment into the system of radiological protection

Risks posed by the presence of radionuclides in the environment require an efficient, balanced, and adaptable assessment for protecting exposed humans and wildlife, and managing the associated radiological risk. Exposure of humans and wildlife originate from the same sources releasing radionuclides to the environment. Environmental concentrations of radionuclides serve as inputs to estimate the dose to man, fauna, and flora, with transfer processes being, in essence, similar, which calls for a common use of transport models. Dose estimates are compared with the radiological protection criteria for humans and wildlife, such as those developed by the International Commission on Radiological Protection. This indicates a similarity in the approaches for impact assessment in humans and wildlife, although some elements are different (e.g. the protection endpoint for humans is stochastic effects on individuals, whereas for wildlife, it is deterministic effects on species and ecosystems). Human and environmental assessments are consistent and complementary in terms of how they are conducted and in terms of the underlying databases (where appropriate). Not having an integrated approach may cause difficulties for operators and regulators, for communication to stakeholders, and may even hamper decision making. For optimised risk assessment and management, the impact from non-radiation contaminants and stressors should also be considered. Both in terms of the underlying philosophy and the application via appropriate tools, the European Radioecology Alliance (ALLIANCE) upholds that integration of human and ecological impact and risk assessment is recommended from several perspectives (e.g. chemical/radiological risks).

Whole organism to tissue concentration ratios derived from an Australian tropical dataset

Whole organism to tissue concentration ratios (CR_wo-tissue) were derived for six wildlife groups (freshwater birds, freshwater bivalves, freshwater fishes, freshwater reptiles, freshwater vascular plants and terrestrial mammals). The wildlife groups and data represented species common to tropical northern Australia. Values of CR_wo-tissue were derived for between 6 and 34 elements, depending upon wildlife group. The values were generally similar to international reference values. However, differences for some element-tissue combinations could affect radiation dose estimates for wildlife in certain environmental exposure situations, including uranium mining, where these data are intended to be applied.

Marine radioecology after the Fukushima Dai-ichi nuclear accident: Are we better positioned to understand the impact of radionuclides in marine ecosystems?

This paper focuses on how a community of researchers under the COMET (CO-ordination and iMplementation of a pan European projecT for radioecology) project has improved the capacity of marine radioecology to understand at the process level the behaviour of radionuclides in the marine environment, uptake by organisms and the resulting doses after the Fukushima Dai-ichi nuclear accident occurred in 2011. We present new radioecological understanding of the processes involved, such as the interaction of waterborne radionuclides with suspended particles and sediments or the biological uptake and turnover of radionuclides, which have been better quantified and mathematically described. We demonstrate that biokinetic models can better represent radionuclide transfer to biota in non-equilibrium situations, bringing more realism to predictions, especially when combining physical, chemical and biological interactions that occur in such an open and dynamic environment as the ocean. As a result, we are readier now than we were before the FDNPP accident in terms of having models that can be applied to dynamic situations. The paper concludes with our vision for marine radioecology as a fundamental research discipline and we present a strategy for our discipline at the European and international levels. The lessons learned are presented along with their possible applicability to assess/reduce the environmental consequences of future accidents to the marine environment and guidance for future research, as well as to assure the sustainability of marine radioecology. This guidance necessarily reflects on why and where further research funding is needed, signalling the way for future investigations.

Ecotracer: analyzing concentration of contaminants and radioisotopes in an aquatic spatial-dynamic food web model

Ecotracer is a tool in the Ecopath with Ecosim (EwE) software package used to simulate and analyze the transport of contaminants such as methylmercury or radiocesium through aquatic food webs. Ecotracer solves the contaminant dynamic equations simultaneously with the biomass dynamic equations in Ecosim/Ecospace. In this paper, we give a detailed description of the Ecotracer module and analyze the performance on two problems of differing complexity. Ecotracer was modified from previous versions to more accurately model contaminant excretion, and new numerical integration algorithms were implemented to increase accuracy and robustness. To test the mathematical robustness of the computational algorithm, Ecotracer was tested on a simple problem for which we know an analytical solution. These results demonstrated the effectiveness of the program numerics. A much more complex model, the release of the cesium radionuclide ¹³⁷Cs from the Fukushima Dai-ichi nuclear accident, was also modeled and analyzed. A comparison of the Ecotracer results to sampled ¹³⁷Cs measurements in the coastal ocean area around Fukushima show the promise of the tool but also highlight some important limitations.

On the divergences in assessment of environmental impacts from ionising radiation following the Fukushima accident

The accident at the Fukushima-Daiichi Nuclear Power Station on March 11, 2011, led to significant contamination of the surrounding terrestrial and marine environments. Whilst impacts on human health remain the primary concern in the aftermath of such an accident, recent years have seen a significant body of work conducted on the assessment of the accident's impacts on both the terrestrial and marine environment. Such assessments have been undertaken at various levels of biological organisation, for different species, using different methodologies and coming, in many cases, to divergent conclusions as to the effects of the accident on the environment. This article provides an overview of the work conducted in relation to the environmental impacts of the Fukushima accident, critically comparing and contrasting methodologies and results with a view towards finding reasons for discrepancies, should they indeed exist. Based on the outcomes of studies conducted to date, it would appear that in order to avoid the fractured and disparate conclusions drawn in the aftermath of previous accidents, radioactive contaminants and their effects can no longer simply be viewed in isolation with respect to the ecosystems these effects may impact. A combination of laboratory based and field studies with a focus on ecosystem functioning and effects could offer the best opportunities for coherence in the interpretation of the results of studies into the environmental impacts of ionising radiation.

Impacts on the marine environment in the case of a hypothetical accident involving the recovery of the dumped Russian submarine K-27, based on dispersion of 137Cs

There is increasing concern regarding the issue of dumped nuclear waste in the Arctic Seas and in particular dumped objects with Spent Nuclear Fuel (SNF). Amongst dumped objects in the Arctic, the dumped Russian submarine K-27 has received great attention as it contains two reactors with highly enriched fuel and lies at a depth of about 30 m under water. To address these concerns a health and environmental impact assessment has been undertaken. Marine dispersion of potentially released radionuclides as a consequence of different hypothetical accident scenarios was modelled using the model NAOSIM. The outputs from the dispersion modelling have been used as inputs to food-chain transfer and environmental dosimetry models. The annual effective doses for subsistence fishing communities of the Barents-Kara seas region do not exceed 0.6 mSv for hypothetical accidents located at Stepovogo fjord or the Barents Sea. For high rate consumers of fish in Norway, following a potential accident at the Gremikha Bay, annual effects doses would be at around 0.15 mSv. Accumulated doses (over 90 days) for various organisms and for all release scenarios considered were never in excess of 150 μGy. The levels of ¹³⁷Cs derived for marine organism in areas close to Norway were not values that would likely cause concern from a regulatory perspective although for subsistence fishing communities close to the considered accident locations, it is not inconceivable that some restrictions on fishing etc. would need to be introduced.

A tool for calculating concentration ratios from large environmental datasets

This paper presents a tool for calculating concentration ratios from a large and structured environmental dataset of radionuclide activity and metal concentrations. The tool has been developed in MS Excel™ and includes a simple user interface for setting up queries. The tool is capable of matching environmental media samples to biota samples based on user-defined spatial and temporal criteria to derive a representative estimate of the environmental exposure conditions of an organism and its accumulation. Some potential benefits and uses of the tool are discussed.

Impact of the Fukushima accident on marine biota, five years later

In a previous commentary written in 2011 in the aftermath of the Fukushima accident in Japan, I summarized what was then understood about the effects of accidental radioactive discharges to marine life and forecasted into the future how the marine environment would likely be affected. Since that time, several studies have been conducted on the impact of the accident on marine organisms, and radiation doses arising thereof. I developed a dynamic transfer model for studying the bioaccumulation of Fukushima radionuclides in marine biota and assessed the impact and likelihood of effects to marine life. In the present article, I highlight the lessons learned over the past 5 years. I address whether the environmental consequences in the marine environment are as significant as initially feared and, with respect to the current situation, what remains to be investigated as the radioactivity continues to spread in the marine environment. Integr Environ Assess Manag 2016;12:654-658. © 2016 SETAC.

Derivation of risk indices and analysis of variablility for the management of incidents involving the transport of nuclear materials in the Northern Seas

The transport of nuclear or radioactive materials and the presence of nuclear powered vessels pose risks to the Northern Seas in terms of potential impacts to man and environment as well socio-economic impacts. Management of incidents involving actual or potential releases to the marine environment are potentially difficult due to the complexity of the environment into which the release may occur and difficulties in quantifying risk to both man and environment. In order to address this, a state of the art oceanographic model was used to characterize the underlying variability for a specific radionuclide release scenario. The resultant probabilistic data were used as inputs to transfer and dose models providing an indication of potential impacts for man and environment This characterization was then employed to facilitate a rapid means of quantifying risk to man and the environment that included and addressed this variability. The radionuclide specific risk indices derived can be applied by simply multiplying the reported values by the magnitude of the source term and thereafter summing over all radionuclides to provide an indication of total risk.

Inter-comparison of dynamic models for radionuclide transfer to marine biota in a Fukushima accident scenario

We report an inter-comparison of eight models designed to predict the radiological exposure of radionuclides in marine biota. The models were required to simulate dynamically the uptake and turnover of radionuclides by marine organisms. Model predictions of radionuclide uptake and turnover using kinetic calculations based on biological half-life (TB1/2) and/or more complex metabolic modelling approaches were used to predict activity concentrations and, consequently, dose rates of (90)Sr, (131)I and (137)Cs to fish, crustaceans, macroalgae and molluscs under circumstances where the water concentrations are changing with time. For comparison, the ERICA Tool, a model commonly used in environmental assessment, and which uses equilibrium concentration ratios, was also used. As input to the models we used hydrodynamic forecasts of water and sediment activity concentrations using a simulated scenario reflecting the Fukushima accident releases. Although model variability is important, the intercomparison gives logical results, in that the dynamic models predict consistently a pattern of delayed rise of activity concentration in biota and slow decline instead of the instantaneous equilibrium with the activity concentration in seawater predicted by the ERICA Tool. The differences between ERICA and the dynamic models increase the shorter the TB1/2 becomes; however, there is significant variability between models, underpinned by parameter and methodological differences between them. The need to validate the dynamic models used in this intercomparison has been highlighted, particularly in regards to optimisation of the model biokinetic parameters.

Dynamic modelling of radionuclide uptake by marine biota: application to the Fukushima nuclear power plant accident

The dynamic model D-DAT was developed to study the dynamics of radionuclide uptake and turnover in biota and sediments in the immediate aftermath of the Fukushima accident. This dynamics is determined by the interplay between the residence time of radionuclides in seawater/sediments and the biological half-lives of elimination by the biota. The model calculates time-variable activity concentration of (131)I, (134)Cs, (137)Cs and (90)Sr in seabed sediment, fish, crustaceans, molluscs and macroalgae from surrounding activity concentrations in seawater, with which to derive internal and external dose rates. A central element of the model is the inclusion of dynamic transfer of radionuclides to/from sediments by factorising the depletion of radionuclides adsorbed onto suspended particulates, molecular diffusion, pore water mixing and bioturbation, represented by a simple set of differential equations coupled with the biological uptake/turnover processes. In this way, the model is capable of reproducing activity concentration in sediment more realistically. The model was used to assess the radiological impact of the Fukushima accident on marine biota in the acute phase of the accident. Sediment and biota activity concentrations are within the wide range of actual monitoring data. Activity concentrations in marine biota are thus shown to be better calculated by a dynamic model than with the simpler equilibrium approach based on concentration factors, which tends to overestimate for the acute accident period. Modelled dose rates from external exposure from sediment are also significantly below equilibrium predictions. The model calculations confirm previous studies showing that radioactivity levels in marine biota have been generally below the levels necessary to cause a measurable effect on populations. The model was used in mass-balance mode to calculate total integrated releases of 103, 30 and 3 PBq for (131)I, (137)Cs and (90)Sr, reasonably in line with previous estimates.

Making the most of what we have: application of extrapolation approaches in radioecological wildlife transfer models

We will never have data to populate all of the potential radioecological modelling parameters required for wildlife assessments. Therefore, we need robust extrapolation approaches which allow us to make best use of our available knowledge. This paper reviews and, in some cases, develops, tests and validates some of the suggested extrapolation approaches. The concentration ratio (CRproduct-diet or CRwo-diet) is shown to be a generic (trans-species) parameter which should enable the more abundant data for farm animals to be applied to wild species. An allometric model for predicting the biological half-life of radionuclides in vertebrates is further tested and generally shown to perform acceptably. However, to fully exploit allometry we need to understand why some elements do not scale to expected values. For aquatic ecosystems, the relationship between log10(a) (a parameter from the allometric relationship for the organism-water concentration ratio) and log(Kd) presents a potential opportunity to estimate concentration ratios using Kd values. An alternative approach to the CRwo-media model proposed for estimating the transfer of radionuclides to freshwater fish is used to satisfactorily predict activity concentrations in fish of different species from three lakes. We recommend that this approach (REML modelling) be further investigated and developed for other radionuclides and across a wider range of organisms and ecosystems. Ecological stoichiometry shows potential as an extrapolation method in radioecology, either from one element to another or from one species to another. Although some of the approaches considered require further development and testing, we demonstrate the potential to significantly improve predictions of radionuclide transfer to wildlife by making better use of available data.

Development of emergency response tools for accidental radiological contamination of French coastal areas

The Fukushima nuclear accident resulted in the largest ever accidental release of artificial radionuclides in coastal waters. This accident has shown the importance of marine assessment capabilities for emergency response and the need to develop tools for adequately predicting the evolution and potential impact of radioactive releases to the marine environment. The French Institute for Radiological Protection and Nuclear Safety (IRSN) equips its emergency response centre with operational tools to assist experts and decision makers in the event of accidental atmospheric releases and contamination of the terrestrial environment. The on-going project aims to develop tools for the management of marine contamination events in French coastal areas. This should allow us to evaluate and anticipate post-accident conditions, including potential contamination sites, contamination levels and potential consequences. In order to achieve this goal, two complementary tools are developed: site-specific marine data sheets and a dedicated simulation tool (STERNE, Simulation du Transport et du transfert d'Eléments Radioactifs dans l'environNEment marin). Marine data sheets are used to summarize the marine environment characteristics of the various sites considered, and to identify vulnerable areas requiring implementation of population protection measures, such as aquaculture areas, beaches or industrial water intakes, as well as areas of major ecological interest. Local climatological data (dominant sea currents as a function of meteorological or tidal conditions) serving as the basis for an initial environmental sampling strategy is provided whenever possible, along with a list of possible local contacts for operational management purposes. The STERNE simulation tool is designed to predict radionuclide dispersion and contamination in seawater and marine species by incorporating spatio-temporal data. 3D hydrodynamic forecasts are used as input data. Direct discharge points or atmospheric deposition source terms can be taken into account. STERNE calculates Eulerian radionuclide dispersion using advection and diffusion equations established offline from hydrodynamic calculations. A radioecological model based on dynamic transfer equations is implemented to evaluate activity concentrations in aquatic organisms. Essential radioecological parameters (concentration factors and single or multicomponent biological half-lives) have been compiled for main radionuclides and generic marine species (fish, molluscs, crustaceans and algae). Dispersion and transfer calculations are performed simultaneously on a 3D grid. Results can be plotted on maps, with possible tracking of spatio-temporal evolution. Post-processing and visualization can then be performed.

Radionuclide biological half-life values for terrestrial and aquatic wildlife

The equilibrium concentration ratio is typically the parameter used to estimate organism activity concentrations within wildlife dose assessment tools. Whilst this is assumed to be fit for purpose, there are scenarios such as accidental or irregular, fluctuating, releases from licensed facilities when this might not be the case. In such circumstances, the concentration ratio approach may under- or over-estimate radiation exposure depending upon the time since the release. To carrying out assessments for such releases, a dynamic approach is needed. The simplest and most practical option is representing the uptake and turnover processes by first-order kinetics, for which organism- and element-specific biological half-life data are required. In this paper we describe the development of a freely available international database of radionuclide biological half-life values. The database includes 1907 entries for terrestrial, freshwater, riparian and marine organisms. Biological half-life values are reported for 52 elements across a range of wildlife groups (marine = 9, freshwater = 10, terrestrial = 7 and riparian = 3 groups). Potential applications and limitations of the database are discussed.

Exposures and effects in the marine environment after the Fukushima accident

This paper does not necessarily reflect the views of the International Commission on Radiological Protection. Radiation doses to marine biota near the Fukushima Daiichi nuclear power plant have been estimated for the immediate aftermath and subsequent period of the accident. Dose estimations using monitoring data have been complemented by means of dynamic transfer modelling, improving on the more traditional equilibrium transfer approach. Earlier assessments using equilibrium transfer models overestimated the exposures in the immediate aftermath of the accident, whereas dynamic transfer modelling brings them more in line with the doses calculated from monitored activity concentrations in the biota. On that basis, marine biota populations in the vicinity of Fukushima do not seem to be at significant risk. The situation in the late post-accident period shows a tendency for lower exposures, but radiocaesium in sediments and biota persists to this day, with some organisms inhabiting local hotspots. Little is known about how long radionuclides will continue to remain in the local environment, or the long-term effects on populations due to limited knowledge on the effects of chronic radiation exposures to marine organisms. Therefore, the marine environment at Fukushima needs further study. The Fukushima nuclear accident remains an ongoing problem for marine radioecology, requiring constant re-evaluation of the cumulative extent of contamination and effects on the environment for years to come.

A dynamic model to estimate the activity concentration and whole body dose rate of marine biota as consequences of a nuclear accident

This paper describes a dynamic compartment model (K-BIOTA-DYN-M) to assess the activity concentration and whole body dose rate of marine biota as a result of a nuclear accident. The model considers the transport of radioactivity between the marine biota through the food chain, and applies the first order kinetic model for the sedimentation of radionuclides from seawater onto sediment. A set of ordinary differential equations representing the model are simultaneously solved to calculate the activity concentration of the biota and the sediment, and subsequently the dose rates, given the seawater activity concentration. The model was applied to investigate the long-term effect of the Fukushima nuclear accident on the marine biota using (131)I, (134)Cs, and, (137)Cs activity concentrations of seawater measured for up to about 2.5 years after the accident at two locations in the port of the Fukushima Daiichi Nuclear Power Station (FDNPS) which was the most highly contaminated area. The predicted results showed that the accumulated dose for 3 months after the accident was about 4-4.5Gy, indicating the possibility of occurrence of an acute radiation effect in the early phase after the Fukushima accident; however, the total dose rate for most organisms studied was usually below the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation)'s bench mark level for chronic exposure except for the initial phase of the accident, suggesting a very limited radiological effect on the marine biota at the population level. The predicted Cs sediment activity by the first-order kinetic model for the sedimentation was in a good agreement with the measured activity concentration. By varying the ecological parameter values, the present model was able to predict the very scattered (137)Cs activity concentrations of fishes measured in the port of FDNPS. Conclusively, the present dynamic model can be usefully applied to estimate the activity concentration and whole body dose rate of the marine biota as the consequence of a nuclear accident.

Using an Ecosystem Approach to complement protection schemes based on organism-level endpoints

Radiation protection goals for ecological resources are focussed on ecological structures and functions at population-, community-, and ecosystem-levels. The current approach to radiation safety for non-human biota relies on organism-level endpoints, and as such is not aligned with the stated overarching protection goals of international agencies. Exposure to stressors can trigger non-linear changes in ecosystem structure and function that cannot be predicted from effects on individual organisms. From the ecological sciences, we know that important interactive dynamics related to such emergent properties determine the flows of goods and services in ecological systems that human societies rely upon. A previous Task Group of the IUR (International Union of Radioecology) has presented the rationale for adding an Ecosystem Approach to the suite of tools available to manage radiation safety. In this paper, we summarize the arguments for an Ecosystem Approach and identify next steps and challenges ahead pertaining to developing and implementing a practical Ecosystem Approach to complement organism-level endpoints currently used in radiation safety.

The impact of the Fukushima nuclear accident on marine biota: retrospective assessment of the first year and perspectives

An international study under the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was performed to assess radiological impact of the nuclear accident at the Fukushima-Daiichi Nuclear Power Station (FDNPS) on the marine environment. This work constitutes the first international assessment of this type, drawing upon methodologies that incorporate the most up-to-date radioecological models and knowledge. To quantify the radiological impact on marine wildlife, a suite of state-of-the-art approaches to assess exposures to Fukushima derived radionuclides of marine biota, including predictive dynamic transfer modelling, was applied to a comprehensive dataset consisting of over 500 sediment, 6000 seawater and 5000 biota data points representative of the geographically relevant area during the first year after the accident. The dataset covers the period from May 2011 to August 2012. The method used to evaluate the ecological impact consists of comparing dose (rates) to which living species of interest are exposed during a defined period to critical effects values arising from the literature. The assessed doses follow a highly variable pattern and generally do not seem to indicate the potential for effects. A possible exception of a transient nature is the relatively contaminated area in the vicinity of the discharge point, where effects on sensitive endpoints in individual plants and animals might have occurred in the weeks directly following the accident. However, impacts on population integrity would have been unlikely due to the short duration and the limited space area of the initially high exposures. Our understanding of the biological impact of radiation on chronically exposed plants and animals continues to evolve, and still needs to be improved through future studies in the FDNPS marine environment.

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.

Predicting the environmental risks of radioactive discharges from Belgian nuclear power plants

An environmental risk assessment (ERA) was performed to evaluate the impact on non-human biota from liquid and atmospheric radioactive discharges by the Belgian Nuclear Power Plants (NPP) of Doel and Tihange. For both sites, characterisation of the source term and wildlife population around the NPPs was provided, whereupon the selection of reference organisms and the general approach taken for the environmental risk assessment was established. A deterministic risk assessment for aquatic and terrestrial ecosystems was performed using the ERICA assessment tool and applying the ERICA screening value of 10 μGy h(-1). The study was performed for the radioactive discharge limits and for the actual releases (maxima and averages over the period 1999-2008 or 2000-2009). It is concluded that the current discharge limits for the Belgian NPPs considered do not result in significant risks to the aquatic and terrestrial environment and that the actual discharges, which are a fraction of the release limits, are unlikely to harm the environment.

Time-dependent transfer of 137Cs, 85Sr and 65Zn to earthworms in highly contaminated soils

The transfer characteristics of (137)Cs, (85)Sr and (65)Zn to earthworms (Eisenia andrei) in soils with different amounts of the radionuclides have been investigated. The time-dependent whole-body concentration ratios (CR) were derived for worms in artificially contaminated soils with three different activity concentrations. Two parameters of a first order kinetic model, the equilibrium concentration ratio (CR(eq)) and the effective loss rate constant (k), were estimated by a comparison of experimental CR results with model predictions. The estimated CR(eq) (Bq/kg fresh worm per Bq/kg dry soil) ranged from 3.9 × 10(-4) to 4.1 × 10(-3) for (137)Cs, 1.39 × 10(-3) to 2.94 × 10(-2) for (85)Sr, and 1.39 × 10(-3) to 5.0 × 10(-2) for (65)Zn, and consistently decreased with increasing soil activity concentration but the trend was not statistically significant. The CR(eq) for (137)Cs was one to two orders of magnitude lower than previously reported CR(wo-soil) values (based on field data with much less contaminated soil), that for (85)Sr was comparable with other reported values and for (65)Zn was less two to three orders of magnitude lower than CR(wo-soil) values for stable zinc. The estimated k (d(-1)) values ranged from 9 × 10(-2) to 1.4 × 10(-1) for (137)Cs, 7 × 10(-2) to 2 × 10(-1) for (85)Sr, and 6 × 10(-2) to 1.8 × 10(-1) for (65)Zn, and did not show a relationship with soil activity concentration. The effect of CR(eq) on the total dose rate was insignificant for (137)Cs or (65)Zn because external dose rates to the soil dwelling earthworms due to these radionuclides were much greater than the internal dose rate. In contrast, the total dose from (90)Sr was determined by the internal dose rate and therefore proportional to the CR(eq).

TRS Cs CRwo-water values for the marine environment: analysis, applications and comparisons

A new TRS document on Transfer of radionuclides to Wildlife has compiled equilibrium CR(wo-media) values for a variety of radionuclides and ecosystems. Assessment tools such as the ERICA Tool use equilibrium whole organism concentration ratios (CR(wo-media)) to predict radionuclide activity concentrations in wildlife from those in media (e.g. water). The aim of this paper is to compare and contrast model predictions of doses from (137)Cs to marine organisms using three different approaches: (i) the ERICA Tool utilising the new TRS values to estimate internal and external doses to reference organisms for the Black sea and the Aegean Sea and for the sea close to the Fukushima Dai-ichi plant. (ii) a hydrodynamic site specific model for seawater for parts of the Aegean Sea, Greece which estimates radionuclide concentrations using site specific data and (iii) a biokinetic model for fish applied to the Fukushima releases to the Pacific. The advantages and limitations of these approaches are discussed with respect to determining doses to pelagic fish. The applicability of the three approaches will vary with the objective of an assessment. The site specific model can predict variation in (137)Cs with depth and uses site specific CR values. The application of the biokinetic model to predicted (137)Cs activity concentrations in seawater and fish due to near coastal inputs from Fukushima Dai-ichi showed that the maximum internal dose-rates in fish attributable to (137)Cs would be substantially lower than those determined using equilibrium assumptions in ERICA but the accumulative doses over 100 days were similar.

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.

Pre- and post-Chernobyl accident levels of 129I and 137Cs in the Southern Baltic Sea by brown seaweed Fucus vesiculosus

(129)I is a very long-lived radionuclide (T(1/2) = 15.7 × 10(6) years) that is present in the environment both because of natural and anthropogenic sources. In this work (129)I concentration and (129)I/(127)I ratio have been determined in seaweed Fucus vesiculosus collected in the Southern Baltic Sea during 1982 and 1986 (post-Chernobyl accident). The resulting data were evaluated in terms of (129)I concentrations, (129)I/(127)I and (129)I/(137)Cs ratios. (129)I concentrations were found to be in the order of (0.82-5.89) × 10(9) atoms g(-1) in 1982 and (1.33-38.83) × 10(9) atoms g(-1) in 1986. The (129)I/(127)I ratios ranged from (22.7-87.8) × 10(-10) for seaweed collected in 1982 and from (26.1-305.5) × 10(-10) for seaweed collected in 1986. Also a linear relationship was established for (127)I concentrations in seawater and salinity in this area, enabling the estimation of concentration factors for (127)I in F. vesiculosus. The high levels of (129)I and (129)I/(127)I in the Kattegat and their gradually decreasing trend to the Baltic Sea indicates that the most important contribution to the (129)I inventory in the Baltic Sea area comes from Sellafield and La Hague reprocessing plants. With respect to Chernobyl accident, (129)I concentrations in samples collected in 1986 were not much higher than those expected in less contaminated samples from 1982. This supports the view that the contribution of the Chernobyl accident to (129)I in the Baltic region was not significant.

Dose assessment for marine biota and humans from discharge of (131)I to the marine environment and uptake by algae in Sydney, Australia

Iodine-131 reaches the marine environment through its excretion to the sewer by nuclear medicine patients followed by discharge through coastal and deepwater out falls. 131I has been detected in macroalgae,which bio-accumulate iodine, growing near the coastal out fall of Cronulla sewage treatment plant (STP) since 1995. During this study, (131)I levels in liquid effluent and sludge from three Sydney STP's as well as in macroalgae (Ulva sp. and Ecklonia radiata) growing near their shoreline out falls were measured. Concentration factors of 176 for Ulva sp. and 526 for E. radiata were derived. Radiation dose rates to marine biota from (131)I discharged to coastal waters calculated using the ERICA dose assessment tool were below the ERICA screening level of 10 μGy/hr. Radiation dose rates to humans from immersion in seawater or consumption of Ulva sp. containing (131)I were three and two orders of magnitude below the IAEA screening level of 10 μSv/year, respectively.

Impact of nuclear accidents on marine biota

The accident at the Fukushima Daiichi nuclear power plant, precipitated by the earthquake and subsequent tsunami that struck the northeastern coast of Japan in March 2011, has raised concerns about the potential impact to marine biota posed by the release of radioactive water and radionuclide particles into the environment. The Fukushima accident is the only major nuclear accident that has resulted in the direct discharge of radioactive materials into a coastal environment. This article briefly summarizes what is currently understood about the effects of radioactive wastewaters and radionuclides to marine life.

An approach for the assessment of risk from chronic radiation to populations of phytoplankton and zooplankton

A conceptual model of the effects of chronic radiation on a population of phytoplankton and zooplankton in an oceanic nutrient layer is presented. The model shows that there are distinct threshold dose rates at which the different plankton populations become unsustainable. These are 10,400 microGy h(-1) for phytoplankton and 125 microGy h(-1) for zooplankton. Both these values are considerably greater than the current screening values for protection of 10 microGy h(-1). The model highlights the effects of predator-prey dynamics in predicting that when the zooplankton is affected by the radiation dose, the phytoplankton population can increase. In addition, the model was altered to replicate the dose rates to the plankton of a previous ERICA Irish Sea assessment (24 microGy h(-1) for zooplankton and 430 microGy h(-1) to phytoplankton). The results showed only a 10% decrease in the zooplankton population and a 15% increase in the phytoplankton population. Therefore, at this level of dose, the model predicts that although the dose rate exceeds the guideline value, populations are not significantly affected. This result highlights the limitations of a single screening value for different groups of organisms.

An approach to the assessment of risk from chronic radiation to populations of European lobster, Homarus gammarus (L.)

The basic principles underlying a four-discrete age group, logistic, growth model for the European lobster Homarus gammarus are presented and discussed at proof-of-concept level. The model considers reproduction, removal by predation, natural death, fishing, radiation and migration. Non-stochastic effects of chronic low linear energy transfer (LET) radiation are modelled with emphasis on (99)Tc, using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher dose rates, mortality. An allometric approach for the calculation of LD(50/30) as a function of the mass of each life stage is used in model calibration. The model predicts that at a dose rate of 1 Gy day(-1), lobster population reproduction and survival become severely compromised, leading eventually to population extinction. At 0.01 Gy day(-1), the survival rate of an isolated population is reduced by 10%, mainly through loss of fecundity, comparable to natural migration losses. Fishing is the main ecological stress and only dose rates in the range 0.03-0.1 Gy day(-1) can achieve discernible effects above it. On the balance of radiation and other ecological stresses, a benchmark value of 0.01 Gy day(-1) is proposed for the protection of lobster populations. This value appears consistent with available information on radiation effects in wildlife.

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.