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

Best practices for predictions of radionuclide activity concentrations and total absorbed dose rates to freshwater organisms exposed to uranium mining/milling.

This is the final version. Available from Elsevier via the DOI in this record.Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisions on the implementation of mitigation measures. The objective of this study was to identify how dose rate modelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, we modelled the activity concentrations of 210Pb, 210Po, 226Ra, 230Th, and 238U downstream of uranium mines and mills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwater food chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentration ratio values from one model to another and including all or only some 238U decay daughters in the dose rate assessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At the initial planning stage, the best-practice approach recommend using conservative site-specific baseline activity concentrations in water, sediments and organisms and predict conservative incremental activity concentrations in these media by selecting concentration ratios based on species similarity and similar water quality conditions to reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practice approach recommends relying on measured activity concentrations in water, sediment, fish tissue and whole-body of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow for more realistic but still conservative dose assessments when evaluating impacts from uranium mining projects and making decision on adequate controls of releases

A boom‐or‐bust approach — the ‘Glass Cannon’ hypothesis in host microbiomes

In Focus: Dunphy, CM, Vollmer, SV, Gouhier, TC. (2021) Host–microbial systems as glass cannons: Explaining microbiome stability in corals exposed to extrinsic perturbations. Journal of Animal Ecology, 90, 1044–1057. The importance of symbiotic microbial communities for the functioning of animal hosts is now well‐documented; however, the interactions between host microbiomes and stress are less well‐understood. Dunphy et al. used a common garden experiment to show that host–microbiomes vary in their resilience across different coral species. The authors then used mathematical modelling to provide novel evidence that species with microbiomes that are regulated by host processes are robust to perturbation from stressors, but that robustness comes at a higher cost to the host. Conversely, species with microbiomes that are regulated by microbial processes are generally much more resilient and cheaper to support, but when disrupted by external stressors, the communities break down entirely—these latter species are termed ‘glass cannons’. This novel hypothesis has important implications for how host microbiomes function in a rapidly changing world that exposes animal hosts to multiple biotic and abiotic perturbations

The assumption of heterogeneous or homogeneous radioactive contamination in soil/sediment Does it matter in terms of the external exposure of fauna?

International audienceThe classical approach to environmental radioprotection is based on the assumption of homogeneously contaminated media. However, in soils and sediments there may be a significant variation of radioactivity with depth. The effect of this heterogeneity was investigated by examining the external exposure of various sediment and soil organisms, and determining the resulting dose rates, assuming a realistic combination of locations and radionuclides. The results were dependent on the exposure situation, i.e., the organism, its location, and the quality and quantity of radionuclides. The dose rates ranged over three orders of magnitude. The assumption of homogeneous contamination was not consistently conservative (if associated with a level of radioactivity averaged over the full thickness of soil or sediment that was sampled). Dose assessment for screening purposes requires consideration of the highest activity concentration measured in a soil/sediment that is considered to be homogeneously contaminated. A more refined assessment (e.g., higher tier of a graded approach) should take into consideration a more realistic contamination profile, and apply different dosimetric approaches. © 2014 Elsevier Ltd

Transformation of measurements into input data for a river model

Before running a calculation code, it is necessary to collect and select the required entry data, data being a fundamental element upon which reasoning as well as research are based. In order to be rigorous, these practical elements should be managed in parallel with the modelling activities, aiming at common targets. For example, such a view is necessary for building relevant experimental designs. Indeed such methods require the collection of measurements through formalised protocols meeting the needs of the code. Such measurements could then define, for given space and duration, relevant data sets to "feed" the code. However, the calculation codes are frequently supplied a posteriori on the basis of measurements collected for other purposes. At first, the corresponding raw information must be collected and then adapted to the model needs, meaning a transformation of measurements into elaborated data. At this stage three kinds of problem exist: access to data, quality of data and quantity of available data. These issues are exposed here as part of the CASTEAUR project (simplified calculation of radionuclides transfer in receiving waterways), actually developed at the IPSN

Effects of soil water content on the external exposure of fauna to radioactive isotopes

International audienceWithin a recent model intercomparison about radiological risk assessment for contaminated wetlands, the influence of soil saturation conditions on external dose rates was evidenced. This issue joined concerns of assessors regarding the choice of the soil moisture value to input in radiological assessment tools such as the ERICA Tool. Does it really influence the assessment results and how? This question was investigated under IAEA's Modelling and Data for Radiological Impacts Assessments (MODARIA) programme via 42 scenarios for which the soil water content varied from 0 (dry soil) to 100% (saturated soil), in combination with other parameters that may influence the values of the external dose conversion coefficients (DCCs) calculated for terrestrial organisms exposed in soil. A set of α, β, and γ emitters was selected in order to cover the range of possible emission energies. The values of their external DCCs varied generally within a factor 1 to 1.5 with the soil water content, excepted for β emitters that appeared more sensitive (DCCs within a factor of about 3). This may be of importance for some specific cases or for upper tiers of radiological assessments, when refinement is required. But for the general purpose of screening assessment of radiological impact on fauna and flora, current approaches regarding the soil water content are relevant. © 2015 Elsevier Ltd

CASTEAUR: A tool for operational assessments of radioactive nuclides transfers in river ecosystems

CASTEAUR (french acronym for Simplified CAlculation of radioactive nuclides Transfer in Receiving WATERways) is an operational tool to assess the impact on fluvial ecosystems of both accidental and routine radioactive releases. This code is organised over a simplified representation of the hydrographic network, on which simplification was applied to the five domains : hydraulics, sedimentary dynamics, ecology and radioecology. The ecosystem could be described by six components which are water, suspended and settled matters, primary producers, first order consumers and fish. According to time and space and with the possibility to take into account four kinds of radioactive releases, from pulse to continuous pollution, CASTEAUR assesses the radioactive nuclides concentrations in these components. These concepts are formalised in a prototype, which offers the possibility to combine the different kind of releases, pollutants and ecosystem components. This paper presents these concepts (hypothesis, models and functionalities) and some application example

Évaluation comparée du risque chimique et du risque radiologique pour l'environnement

The environmental protection is today a global issue that concerns all the human activities. The challenge is to be able to prove their compatibility with the protection of the natural environment, but also if required to manage adequately a potential or established risk, generally in the context of ever strict regulations. Regarding the chemical aspects, known methods are available for the assessment of the associated risk for the environment. From the radiological point of view, the necessity to have such tools recently became more apparent, in order to justify for the public and with a full transparency the release of radioactive substances into the environment, to meet the requirements of the new regulations in terms of environmental protection and finally to harmonize the approaches between human and environmental radioprotection as well as between chemical and radioactive pollutants, simultaneously present for example in routine releases from nuclear power plants. At this end of harmonization, the assessment methodologies of the environmental risk linked to radionuclides or chemical substances are exposed from the theory to their comparative application, a new approach under development from which the first results are summarised. © 2007 EDP Sciences.Protéger l’environnement est aujourd’hui une problématique globale qui concerne toutes les activités de l’homme. Il s’agit donc d’être capable de démontrer la compatibilité de ces activités avec la protection des milieux naturels, mais aussi si nécessaire d’agir pour pallier à un risque potentiel ou avéré, et ce généralement dans le cadre d’une réglementation de plus en plus stricte. Dans le domaine chimique, la prise en compte de cette problématique se traduit par l’existence de méthodes dédiées à l’évaluation du risque environnemental. Dans le domaine radiologique, la nécessité de disposer de tels outils s’est accentuée récemment, afin de pouvoir justifier aux yeux du public et en toute transparence le rejet de substances radioactives dans l’environnement, de répondre aux exigences des nouvelles réglementations en matière de protection de l’environnement et enfin d’harmoniser les approches entre radioprotection humaine et radioprotection de l’environnement, mais aussi entre polluants chimiques et radioactifs, simultanément présents par exemple dans les rejets de routine des centres nucléaires de production d’électricité. Dans cette optique d’harmonisation, les démarches d’évaluation du risque à l’environnement lié à la présence de radionucléides ou de substances chimiques sont présentées depuis les concepts théoriques jusqu’à leur mise en œuvre comparative, approche nouvelle en cours de développement dont les premiers résultats sont présentés

Distribution coefficient Kd of transuranics in soils: Experimental determination and consequences for dose assessment

The distribution coefficient (or Kd) of 241Am between soil and soil solution was estimated on the basis of experiments carried out under controlled conditions for soils displaying pH and organic matter content (which are the relevant parameters for transuranic nuclides sorption ability) found in cultivated soils. In these experiments, designed with five experimental units (batches) per studied contact time, 10 g of dry soil are contaminated with 50 mL of osmosed water containing proper concentrations of the radionuclide. The tracer, initially in nitric form, is neutralized prior to addition with the water, to ensure a constant ionic strength and avoid disturbance of the soil chemistry. After shaking and sedimentation, for each batch, the supernatant is sampled and analyzed by either liquid scintillation or alpha spectrometry. The sorption-desorption kinetic time necessary to reach apparent equilibrium is evaluated (> 10 days). Fixation curves, e.g. activity of the soil vs activity of the solution are established, after measurements, for a single delay representative of the equilibrium, and for a range of several orders of magnitude for radionuclide concentrations. On the basis of several assumptions, Kd values are evaluated by simple linear adjustment. A numerical application to retention half lives in soil is made. Finally, the weight of using site-specific Kd values instead of default parameters, on the doses due to ingestion of terrestrial foodstuffs is discussed for different scenarios