Does the use of reference organisms in radiological impact assessments provide adequate protection of all the species within an environment?

Non-human biota in radiological risk assessment is typically evaluated using Reference Organisms (ROs) or Reference Animals and Plants (RAPs), for all exposure situations. However, it still remains open whether the use of an increased number of species would improve the ability to demonstrate protectiveness of the environment. In this paper, the representativeness of a broader list of fauna is tested in terms of the geometrical characteristics and habits for radiological risk assessments in the case of routine discharges from a nuclear installation: the Cadarache centre. A list of terrestrial animal species, compiled from ecological inventories carried out around it was evaluated. A first survey around the centre inventoried >400 terrestrial fauna species, which were then filtered to reduce the number to 28 species for which dose assessments were carried out. Despite the differences between geometries for those site-specific species and the ROs (including RAPs), the absorbed dose rates calculated for both were very close (within a factor of two). Regardless of the studied organism, the absorbed dose rates calculated for the discharge scenario were mainly related to internal exposure, particularly for tritium (3H) and carbon 14 (14C), showing that there would be an acceptable dose rates difference between species from the same organism group. Additionally, sensitivity analyses were conducted to determine if the use of generic, predefined ROs was enough to assure an adequate protection of endangered species. It was observed that for every radionuclide the difference between assessments for site-specific species and ROs are unlikely to exceed a factor of 3. Hence, the result of this evaluation indicates that the use of generic ROs for non-human biota radiological risk assessment covers sufficiently other species, including endangered ones.

Prevention of Invasive Aspergillus Fungal Infections with the Suspension and Delayed-Release Tablet Formulations of Posaconazole in Patients with Haematologic Malignancies.

Posaconazole is a triazole antifungal used to prevent invasive fungal infections (IFIs) in patients receiving chemotherapy or haemotopoietic stem cell transplantation. Due to highly variable bioavailability of the oral suspension formulation, a delayed-release tablet was developed which showed improved bioavailability. A minimal target posaconazole plasma concentration of 0.7 mg/L is recommended for prophylaxis of IFIs. However, the relationship between plasma concentration of posaconazole and its efficacy against IFIs remains unclear. We analysed trough posaconazole concentrations and response against IFIs in 50 and 104 patients with haematologic malignancies receiving prophylactic posaconazole as the tablet or suspension formulation, respectively. Mean plasma concentration of posaconazole was 1.91 ± 1.06 mg/L and 0.82 ± 0.57 mg/L in the tablet and the oral suspension group, respectively (p < 0.0001). The percentage of patients reaching the minimal target concentration of 0.7 mg/L was 92.0% and 47.1% in the tablet and oral suspension groups, respectively (p < 0.0001). Emergent aspergillosis occurred in 9 (8.7%) patients in the suspension group and in none of the patients taking the tablet formulation (p = 0.032). Our results show a relationship between plasma concentrations of posaconazole and its prophylactic efficacy in patients with haematologic malignancies. Target posaconazole concentrations are reached more efficiently with the tablet than with the suspension formulation.

Tritium and 14C background levels in pristine aquatic systems and their potential sources of variability.

Tritium and (14)C are currently the two main radionuclides discharged by nuclear industry. Tritium integrates into and closely follows the water cycle and, as shown recently the carbon cycle, as does (14)C (Eyrolle-Boyer et al., 2014a, b). As a result, these two elements persist in both terrestrial and aquatic environments according to the recycling rates of organic matter. Although on average the organically bound tritium (OBT) activity of sediments in pristine rivers does not significantly differ today (2007-2012) from the mean tritiated water (HTO) content on record for rainwater (2.4 ± 0.6 Bq/L and 1.6 ± 0.4 Bq/L, respectively), regional differences are expected depending on the biomass inventories affected by atmospheric global fallout from nuclear testing and the recycling rate of organic matter within watersheds. The results obtained between 2007 and 2012 for (14)C show that the levels varied between 94.5 ± 1.5 and 234 ± 2.7 Bq/kg of C for the sediments in French rivers and across a slightly higher range of 199 ± 1.3 to 238 ± 3.1 Bq/kg of C for fish. This variation is most probably due to preferential uptake of some organic carbon compounds by fish restraining (14)C dilution with refractory organic carbon and/or with old carbonates both depleted in (14)C. Overall, most of these ranges of values are below the mean baseline value for the terrestrial environment (232.0 ± 1.8 Bq/kg of C in 2012, Roussel-Debet, 2014a) in relation to dilution by the carbonates and/or fossil organic carbon present in aquatic systems. This emphasises yet again the value of establishing regional baseline value ranges for these two radionuclides in order to account for palaeoclimatic and lithological variations. Besides, our results obtained from sedimentary archive investigation have confirmed the delayed contamination of aquatic sediments by tritium from the past nuclear tests atmospheric fallout, as recently demonstrated from data chronicles (Eyrolle-Boyer et al., 2014a,b). Thus Sedimentary archives can be successfully used to reconstruct past (14)C and OBT levels. Additionally, sediment repositories potentially represent significant storages of OBT that may account for in case of further remobilisation. We finally show that floods can significantly affect the OBT and (14)C levels within suspended particles or sediments depending on the origin of particles reinforcing the need to acquire baseline value range at a regional scale.

Andra Environmental Specimen Bank: archiving the environmental chemical quality for long-term monitoring.

Andra Environmental Specimen Bank (ESB) was established in 2010 as a part of the Perennial Observatory of the Environment (OPE), ongoing Long-Term Environmental Research Monitoring and Testing System located next to the Underground Research Laboratory (URL) at Bure, Meuse/Haute-Marne, France. The URL is used to study the deep geological disposal of high and intermediate level radioactive waste. Andra ESB is designed to archive during at least 100 years samples collected to define the initial state of environmental quality of the local area before the construction of industrial facilities and to ensure the traceability of long-term series of samples collected by the OPE ( http://www.andra.fr/ope ), using safe long-term conservation practices. Samples archived in the bank include some local food chain products (milk, cheese, honey, cereals, grass, cherry plum…) and specimen usually archived internationally to monitor the environmental quality (soil, sediment, water, fish, tree leaves, wild life, etc.). Regarding the different samples and analytical issues, three conservation modalities and facilities were designed: dry conservation under controlled temperature and humidity, cryopreservation in liquid nitrogen (LN2) vapor phase freezers (-150 °C) and in deep-freezing at -80 °C for temporary storage and raw samples before preparation. Andra ESB is equipped with a sample preparation clean room, certified ISO Class 5, dedicated to cryopreservation. This paper describes this first French experiment of long-term chemical quality monitoring and samples cryopreservation of different ecosystems and environmental compartments.

Influence of forest trees on the distribution of mineral weathering-associated bacterial communities of the Scleroderma citrinum mycorrhizosphere.

In acidic forest soils, availability of inorganic nutrients is a tree-growth-limiting factor. A hypothesis to explain sustainable forest development proposes that tree roots select soil microbes involved in central biogeochemical processes, such as mineral weathering, that may contribute to nutrient mobilization and tree nutrition. Here we showed, by combining soil analyses with cultivation-dependent analyses of the culturable bacterial communities associated with the widespread mycorrhizal fungus Scleroderma citrinum, a significant enrichment of bacterial isolates with efficient mineral weathering potentials around the oak and beech mycorrhizal roots compared to bulk soil. Such a difference did not exist in the rhizosphere of Norway spruce. The mineral weathering ability of the bacterial isolates was assessed using a microplaque assay that measures the pH and the amount of iron released from biotite. Using this microplate assay, we demonstrated that the bacterial isolates harboring the most efficient mineral weathering potential belonged to the Burkholderia genus. Notably, previous work revealed that oak and beech harbored very similar pHs in the 5- to 10-cm horizon in both rhizosphere and bulk soil environments. In the spruce rhizosphere, in contrast, the pH was significantly lower than that in bulk soil. Because the production of protons is one of the main mechanisms responsible for mineral weathering, our results suggest that certain tree species have developed indirect strategies for mineral weathering in nutrient-poor soils, which lie in the selection of bacterial communities with efficient mineral weathering potentials.

Assessing the fate of radioactive nickel in cultivated soil cores.

Parameters regarding fate of (63)Ni in the soil-plant system (soil: solution distribution coefficient, K(d) and soil plant concentration ratio, CR) are mostly determined in controlled pot experiments or from simple models involving a limited set of soil parameters. However, as migration of pollutants in soil is strongly linked to the water migration, variation of soil structure in the field and seasonal variation of evapotranspiration will affect these two parameters. The aim of this work was to explore to what extent the downward transfer of (63)Ni and its uptake by plants from surface-contaminated undisturbed soil cores under cultivation can be explained by isotopic dilution of this radionuclide in the pool of stable Ni of soils. Undisturbed soil cores (50 cm x 50 cm) were sampled from a brown rendzina (Rendzic Leptosol), a colluvial brown soil (Fluvic Cambisol) and an acidic brown soil (Dystric Cambisol) using PVC lysimeter tubes (three lysimeters sampled per soil type). Each core was equipped with a leachate collector. Cores were placed in a greenhouse and maize (DEA, Pioneer) was sown. After 44 days, an irrigation was simulated at the core surfaces to supply 10 000 Bq (63)NiCl(2). Maize was harvested 135 days after (63)Ni input and radioactivity determined in both vegetal and water samples. Effective uptake of (63)Ni by maize was calculated for leaves and kernels. Water drainage and leaching of (63)Ni were monitored over the course of the experiment. Values of K(d) in surface soil samples were calculated from measured parameters of isotopic exchange kinetics. Results confirmed that (63)Ni was strongly retained at the soil surface. Prediction of the (63)Ni downward transfer could not be reliably assessed using the K(d) values, since the soil structure, which controls local water fluxes, also affected both water and Ni transport. In terms of (63)Ni plant uptake, the effective uptake in undisturbed soil cores is controlled by isotope dilution as previously shown at the pot experiment scale.

The role of analogues in radioecology.

If no data are available for a specific radionuclide its analogue could be used in radioecological models. They might be used not only in the frame of screening modelling. Relevant processes and features have to be known, such as time scales of these processes, physical, chemical and biological properties of the environment and relevant media. An analogue could only be proven to be valid by comparing its behaviour in the conditions of interest, while confidence in the validity of an analogue will increase as the quality of the justification increases, there will always be some residual uncertainty. Several main types of analogy can be used when measured or recommended values are not available: the same parameter obtained for another isotope of the same element; the same parameter obtained for another element; a different parameter obtained for the same element. There are several cases, when analogues might be applied as indicators of the determining processes in the radioecological studies.

Impact of ectomycorrhizosphere on the functional diversity of soil bacterial and fungal communities from a forest stand in relation to nutrient mobilization processes.

The ectomycorrhizal symbiosis alters the physicochemical and biological conditions in the surrounding soil, thus creating a particular environment called ectomycorrhizosphere, which selects microbial communities suspected to play a role in gross production and nutrient cycling. To assess the ectomycorrhizosphere effect on the structure of microbial communities potentially involved in the mobilization of nutrients from the soil minerals in a poor-nutrient environment, we compared the functional diversity of soil and ectomycorrhizosphere bacterial communities in a forest stand. Two hundred and sixty-four bacterial strains and 107 fungal strains were isolated from the bulk soil of an oak (Quercus petraea) stand and from oak-Scleroderma citrinum ectomycorrhizosphere and ectomycorrhizae, in two soil organo-mineral horizons (0 to 3 cm and 5 to 10 cm). They were characterized using two in vitro tests related to their capacities to mobilize iron and phosphorus. We demonstrated that the oak-S. citrinum ectomycorrhizosphere significantly structures the culturable bacterial communities in the two soil horizons by selecting very efficient strains for phosphorus and iron mobilization. This effect was also observed on the diversity of the phosphate-solubilizing fungal communities in the lower soil horizon. A previous study already demonstrated that Laccaria bicolor-Douglas fir ectomycorrhizosphere structures the functional diversity of Pseudomonas fluorescens population in a forest nursery soil. Comparing to it, our work highlights the consistency of the mycorrhizosphere effect on the functional diversity of bacterial and fungal communities in relation to the mineral weathering process, no matter the fungal symbiont, the age and species of the host tree, or the environment (nursery vs forest). We also demonstrated that the intensity of phosphorus and iron mobilization by the ectomycorrhizosphere bacteria isolated from the lower soil horizon was significantly higher compared to that which was isolated from the upper horizon. This reveals for the first time a stratification of the functional diversity of the culturable soil bacterial communities as related to phosphorus and iron mobilization.