Exploring new frontiers in marine radioisotope tracing - adapting to new opportunities and challenges

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cresswell, T., Metian, M., Fisher, N. S., Charmasson, S., Hansman, R. L., Bam, W., Bock, C., & Swarzenski, P. W. Exploring new frontiers in marine radioisotope tracing - adapting to new opportunities and challenges. Frontiers in Marine Science, 7, (2020): 406, doi:10.3389/fmars.2020.00406.Radioisotopes have been used in earth and environmental sciences for over 150 years and provide unique tools to study environmental processes in great detail from a cellular level through to an oceanic basin scale. These nuclear techniques have been employed to understand coastal and marine ecosystems via laboratory and field studies in terms of how aquatic organisms respond to environmental stressors, including temperature, pH, nutrients, metals, organic anthropogenic contaminants, and biological toxins. Global marine issues, such as ocean warming, deoxygenation, plastic pollution, ocean acidification, increased duration, and intensity of toxic harmful algal blooms (HABs), and coastal contamination are all impacting marine environments, thereby imposing various environmental and economic risks. Being able to reliably assess the condition of coastal and marine ecosystems, and how they may respond to future disturbances, can provide vital information for society in the sustainable management of their marine environments. This paper summarizes the historical use of radiotracers in these systems, describes how existing techniques of radioecological tracing can be developed for specific current environmental issues and provides information on emerging issues that would benefit from current and new radiotracer methods. Current challenges with using radioecological tracers and opportunities are highlighted, as well as opportunities to maximize the application of these methods to greatly increase the ability of environmental managers to conduct evidence-based management of coastal and marine ecosystems.The IAEA is grateful for the support provided to its Environment Laboratories by the Government of the Principality of Monaco. This contribution was made within the framework of the IAEA CRP on “Applied radioecological tracers to assess coastal and marine ecosystem health” (K41019)

Fukushima Daiichi-derived radionuclides in the ocean: Transport, fate, and impacts

The events that followed the Tohoku earthquake and tsunami on March 11, 2011, included the loss of power and overheating at the Fukushima Daiichi nuclear power plants, which led to extensive releases of radioactive gases, volatiles, and liquids, particularly to the coastal ocean. The fate of these radionuclides depends in large part on their oceanic geochemistry, physical processes, and biological uptake. Whereas radioactivity on land can be resampled and its distribution mapped, releases to the marine environment are harder to characterize owing to variability in ocean currents and the general challenges of sampling at sea. Five years later, it is appropriate to review what happened in terms of the sources, transport, and fate of these radionuclides in the ocean. In addition to the oceanic behavior of these contaminants, this review considers the potential health effects and societal impacts

Sunlight-Exposed Biofilm Microbial Communities Are Naturally Resistant to Chernobyl Ionizing-Radiation Levels

BACKGROUND: The Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well. METHODOLOGY/PRINCIPAL FINDINGS: To test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates. CONCLUSIONS/SIGNIFICANCE: Our results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation

(CS)-C-137 inventory in sediment near the Rhone mouth: role played by different sources

The low tidal range of the Mediterranean Sea and the high sediment load of the Rhone induce the formation of an important submarine delta. The Cs-137 inventory in sediment on a 480 km(2) area near the Rhone mouth reached 19.6 TBq in 1990. The spatial distribution of both sediment accumulation rates and (CS)-C-137 concentrations in this area confirm the existence of a spatially well-delimited zone, i.e. the prodelta, where both parameters are the highest. Thus, 40% of the total amount of Cs-137 stored in this 480 km(2) area was found within the prodelta (30 km(2)) in the close vicinity of the river mouth. This attests to the efficiency of the (CS)-C-137 trapping by the prodelta sediments. A study on the part the different (CS)-C-137 sources in the Mediterranean Sea play in contributing to this inventory has been carried out. These sources are (i) direct deposition from both global fallout and the Chernobyl accident, (ii) indirect inputs arising from the erosion of surface soils of the Rhone catchment area that were also contaminated by the previous fallout, (iii) liquid effluents from the nuclear industry into the Rhone waters. Assuming that direct deposition is evenly distributed over the study area (480 km(2)) and that the particulate Cs-137 input from the Rhone is entirely trapped in this same area, these sources account for about 50% of the inventory. These hypotheses are unlikely in a coastal area subject to various physical disturbances but they are conservative enough to assess the lower limit of the nuclear liquid releases contribution to this inventory to be 50%.Le faible marnage en mer Méditerranée et les apports solides élevés du Rhône contribuent à la formation d’un important delta sous-marin. L’inventaire en 137Cs dans les sédiments sur une aire de 480 km2 près de l’embouchure du Rhône atteignait 19,6 TBq en 1990. Les distributions spatiales des taux d’accumulation sédimentaire ainsi que des concentrations en 137Cs confirment l’existence d’une zone bien délimitée, le prodelta, où ces deux paramètres sont les plus élevés. Ainsi, 40% de la quantité totale de 137Cs stockée dans cette zone de 480 km2 sont trouvés dans le prodelta (30 km2) au voisinage immédiat de l’embouchure. Ceci atteste de l’efficacité du piégeage du 137Cs dans les sédiments du prodelta. Une étude sur la contribution à cet inventaire des différentes sources de 137Cs en mer Méditerranée est réalisée. Ces sources sont (i) les dépôts directs dus aux retombées globales ainsi qu’aux retombées de l’accident de Tchernobyl, (ii) les apports indirects par le drainage du bassin versant marqué également par ces deux types de retombées, (iii) les rejets liquides des diverses installations nucléaires rhodaniennes. Si l’on suppose une distribution homogène des dépôts directs sur l’aire étudiée (480 km2) et que les apports en 137Cs particulaires par le Rhône sont restés confinés dans cette même zone, ces sources contribuent pour 50% à l’inventaire. Ces hypothèses sont improbables dans une aire côtière soumise à des perturbations variées mais elles sont suffisamment majorantes pour évaluer la contribution minimale des rejets liquides des installations nucléaires à cet inventaire, à savoir 50%

Ecosystem model-based approach for modeling the dynamics of 137Cs transfer to marine plankton populations: Application to the western North Pacific Ocean after the Fukushima nuclear power plant accident

International audienceHuge amounts of radionuclides, especially 137Cs, were released into the western North Pacific Ocean after the Fukushima nuclear power plant (FNPP) accident that occurred on 11 March 2011, resulting in contamination of the marine biota. In this study we developed a radioecological model to estimate 137Cs concentrations in phytoplankton and zooplankton populations representing the lower levels of the pelagic trophic chain. We coupled this model to a lower trophic level ecosystem model and an ocean circulation model to take into account the site-specific environmental conditions in the area. The different radioecological parameters of the model were estimated by calibration, and a sensitivity analysis to parameter uncertainties was carried out, showing a high sensitivity of the model results, especially to the 137Cs concentration in seawater, to the rates of accumulation from water and to the radionuclide assimilation efficiency for zooplankton. The results of the 137Cs concentrations in planktonic populations simulated in this study were then validated through comparison with the data available in the region after the accident. The model results have shown that the maximum concentrations in plankton after the accident were about 2 to 4 orders of magnitude higher than those observed before the accident, depending on the distance from FNPP. Finally, the maximum 137Cs absorbed dose rate for phyto-and zooplankton populations was estimated to be about 5 × 10-2 μGy h-1, and was, therefore, lower than the predicted no-effect dose rate (PNEDR) value of 10 μGy h-1 defined in the ERICA assessment approach. © 2016 Author(s)

Perturbations spatio-temporelles anthropiques sur l'ecosysteme marseillais

A chronological analysis of the disturbances caused to a pelagical ecosystem by domestic and industrial outfalls discharged on the surface of the coastal waters is done. Chronological series of various sampled parameters give evidence two fundamental components, a daily one (the trend) and the other one characterized by a periodicity of about 6 h, both linked to the different phases of human activities. Cross spectral analysis applied to salinity and phytoplankton series has pointed out a 50 min delay in the answer of phytoplankton communities to the periodical salinity variations. The use of the spectral principal components analysis allowed a description of the "hydrological" structure of the studied pelagical environment associated with 3 different frequencies and, on the hand, to reveal the leading part played by mixing processes

Pb-210 and caesium accumulation in the Rhone delta sediments

Pb-210, Cs-137 and Cs-134 profiles were determined on 13 box-cores from the Rhone submarine delta (north-western Mediterranean Sea). Maximum accumulation rates were estimated using the Pb-210 dating method or the evolution of the Cs-137/Cs-134 activity ratio with depth in the sediment. Rates ranged from more than 20 cm year(-1) near the river mouth to 0.2 cm year(-1) on the shelf, decreasing rapidly seawards with a preferential S-SW direction from the mouth in relation to the spreading of surface and bottom nepheloid layers in this area. Mixing and diffusion processes were evidenced by Cs-137 that penetrated to greater depths than expected from the Pb-210 derived accumulation rates. The delta area is an important sink for the riverine inputs. The Cs-137 inventory over the studied area (480 km(2)) was estimated to be 19.6 TBq in 1990, of which more than 40% was found in the prodelta (30 km(2)), in the vicinity of the river mouth. This inventory appears to be well in excess (50%) of both direct and indirect Cs-137 inputs arising from Chernobyl and weapons test fallout in this region. If it is assumed that this excess is due only to liquid discharges by nuclear installations on the Rhone fiver, it represents 20% of the Cs-137 cumulative discharges by the various nuclear power plants and the Marcoule reprocessing giant released between 1961 to 1990. The Pb-210 budget shows that the sediments are also efficient to scavenge elements transported by advection or diffusion on the shelf. The Rhone delta, and more particularly the prodelta area, is thus an effective sink for particle-reactive elements and pollutants

Potential plutonium remobilisation linked to marine sediment resuspension: First estimates based on flume experiments

In coastal environments, resuspension is a key issue regarding contaminant remobilisation from the sediments. A first attempt to quantify both sedimentary bed erosion and related plutonium isotope remobilisation from eroded particles was carried out through flume experiments. Erosion fluxes under controlled hydrodynamic stresses and their resulting plutonium remobilisation were measured for cohesive sediments sampled at several locations (8 to 97 m depth) near the Rhone river mouth (North-western Mediterranean Sea). Surface sediments were characterised in terms of plutonium content (238Pu and 239,240Pu) and particle size distribution. Laboratory resuspension experiments were performed under realistic hydrodynamic conditions close to those prevailing in coastal zones. Critical shear stresses of erosion ranged between 0.068 and 0.087 N m− 2 whereas erosion rate varied within a factor of 3 (57-176 g m− 2 h− 1). After 1 hour of resuspension, the plutonium activity increased in the seawater particulate phase by factors ranging from 2 to 14, depending on the site at which the sediment was sampled. Plutonium fluxes ranged between 2 and 56 mBq m− 2 h− 1 for 239,240Pu depending on location. The highest fluxes were measured for sediments from the deepest site, where the highest Pu activities and mud content were found. During our resuspension experiments, no significant increase was found in dissolved Pu activities. These laboratory experiments have provided a unique opportunity to investigate the behaviour of plutonium at the sediment-water interface in a coastal environment. They emphasised the importance of sediment resuspension in plutonium remobilisation and its possible dispersion on continental shelves