Seafood dose parameters: Updating 210Po retention factors for cooking, decay loss and mariculture.

210Po has been identified as one of the main contributors to ingestion doses to humans, particularly from the consumption of seafood. The amount of 210Po activity concentration data for various types of seafood has increased greatly in recent times. However, to provide realistic seafood dose assessments, most 210Po data requires correction to account for losses that can occur before the seafood is actually consumed. Here we develop generic correction factors for the main processes associated with reduction of 210Po in seafood - leaching during cooking, radioactive decay between harvest and consumption, and sourcing from mariculture versus wild-caught. When seafood is cooked, the overall mean fraction of 210Po retained is 0.74 for all cooking and seafood types, with the means for various seafood types and cooking categories ranging from 0.56 to 1.03. When considering radioactive decay during the period between harvest and consumption, the overall mean fraction remaining is 0.81 across all seafood preservation/packaging types, with estimates ranging from 0.50 (canned seafood) to 0.98 (fresh seafood). Regarding mariculture influence, the available limited data suggest marine fish and crustaceans raised with processed feed have about one order of magnitude lower (×0.10) 210Po muscle content than wild-caught seafood of the same or similar species, although this ratio varies. Overall, this study concludes that 210Po activity concentrations in seafood at the time of ingestion may be reduced to only about 55% compared to when it was harvested. Therefore, correction factors must be applied to any data derived from environmental monitoring in order to achieve realistic dose estimates. The data also suggest lower 210Po ingestion doses for consumers who routinely favour cooked, long shelf-life and farmed fish/crustaceans. However, more data is needed in some categories, especially for cooking of molluscs and seaweed, and for the 210Po content in all farmed seafood.

Numerical modelling of 137Cs content in the pelagic species of the Japanese Pacific coast following the Fukushima Dai-ichi Nuclear Power Plant accident using a size-structured food-web model.

As result of the great east Japan earthquake on March 2011 and the damages of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), huge amount of radionuclides, especially 137Cs, were released to the Japanese Pacific coast. By consequence, several marine species have been contaminated by direct uptake of radionuclides from seawater or through feeding on contaminated preys. In the present study we propose a novel radioecological modelling approach aiming to simulate the radionuclides transfer to pelagic marine species by giving to the organism body-size a key role in the model. We applied the model to estimate the 137Cs content in 14 commercially important species of the North-Western Pacific Ocean after the FDNPP accident. Firstly, we validated the model and evaluated its performance using various observed field data, and we demonstrated the importance of using such modelling approach in radioecological studies. Afterwards, we estimated some radioecological metrics, such as the maximum activity concentration, its corresponding time and the ecological half-life, which are important in assessment of the previous, current and future contamination levels of the studied species. Finally, we estimated the time duration required for each species to reach the pre-accident 137Cs activity concentrations. The results showed that the contamination levels in the planktivorous species have generally reached the pre-accident levels since about 5 years after the accident (since 2016). While in the case of the higher trophic level species, although the activity concentrations are much lower than the regulatory limit for radiocesium in seafood in Japan (100 Bq kg-1), these species still require another 6-14 years (2018-2026) to reach the pre-accident levels.

Platinum in sediments and mussels from the northwestern Mediterranean coast: Temporal and spatial aspects.

Platinum (Pt) is considered a Technology Critical Element (TCE) and an emerging metallic contaminant with increasing release into the environment. Gaps in knowledge and understanding of environmental levels, fate and effects of Pt still exist, especially in the marine environment. This work presents Pt concentrations in the northwestern Mediterranean coast including: (i) temporal variability from sediment cores and farmed mussels in the Toulon Bay (historically affected by intense human activities) and (ii) spatial distribution from recent wild mussels collected along ∼ 700 km coastline with contrasting ecosystems (including natural reserves), quantified using voltammetry and inductively coupled plasma-mass spectrometry. The historical (>100 years) record of Pt in sediments from the Toulon Bay suggests the existence of non-negligible Pt sources older than those related to vehicle emission devices, such as petrol industry and coal-fired activities. A strong Pt increase in more recent sediments (from ∼12 to 16 ng g-1) and mussels (8-fold increase from ∼0.12 to 0.80 ng g-1) covering the past 25 years reflect the overall evolution of Pt demand in Europe (∼20-fold increase for vehicle catalysts in 20 years). Spatial biomonitoring of Pt in mussels along the northwestern Mediterranean coast is assumed to reflect inter-site differences of Pt exposure (0.09-0.66 ng g-1) despite seasonal effect on tissue development. This study highlights the need for thorough and regular monitoring of Pt levels in sediments and biota from urbanized coastal areas in order to better assess the environmental impact of this TCE, including potential risks for marine organisms.

Tritium in river waters from French Mediterranean catchments: Background levels and variability.

Tritium background levels in various environmental compartments are deeply needed in particular to assess radiological impact, especially in river systems where most of releases from nuclear facilities are performed. The present study aims to identify the main environmental factors that influence tritium background levels in rivers at the regional scale. 41 samples were collected from 2014 to 2016 along 17 small rivers in the south of France. All were located out of the influence of direct releases from nuclear facilities. Tritiated water (HTO) concentrations measured in water samples ranged from 0.12±0.11 to 0.86±0.15BqL-1 and HTO concentrations in rains were modelled between 2015 and 2016 over the study period referring to time series acquired from 1963 to 2014 at Thonon-les-Bains monitoring station. The results of tritium concentrations in rivers studied present a significant variability and are more than twice lower than forecasted values in rain. Multiple linear regressions allowed identifying that HTO concentration in rains, watershed area and altitude were the main tested parameters that are linked to the variability of HTO concentrations in the studied rivers. Finally, HTO fluxes delivered to the Mediterranean Sea by French coastal rivers out of influence of nuclear releases were estimated. The results highlight that those account for around 1% of HTO exported while 99% are transferred by the nuclearized Rhone River.

An updated review on tritium in the environment.

Various studies indicated more or less recently that organically bound tritium (OBT) formed from gaseous or liquid tritium releases into the environment potentially accumulates in organisms contradicting hypotheses associated to methods used to assess the biological impact of tritium on humans (ASN, 2010). Increasing research works were then performed during the last decade in order to gain knowledge on this radionuclide expected to be increasingly released by nuclear installations in the near future within the environment. This review focusses on publications of the last decade. New unpublished observations revealing the presence of technogenic tritium in a sedimentary archive collected in the upper reaches of the Rhône river and findings from the Northwestern Mediterranean revealing in all likelihood the impact of terrigenous tritium inputs on OBT levels recorded in living organisms are also presented. Identifying and understanding the physicochemical forms of tritium and the processes leading to its persistence in environmental compartments would explain most observations regarding OBT concentrations in organisms and definitively excludes that tritium would "bio accumulate" within living organisms.

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.

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.

Apparent enrichment of organically bound tritium in rivers explained by the heritage of our past.

The global inventory of naturally produced tritium (3H) is estimated at 2.65 kg, whereas more than 600 kg have been released during atmospheric nuclear tests (NCRP, 1979; UNSCEAR, 2000) constituting the main source of artificial tritium throughout the Anthropocene. The behaviour of this radioactive isotope in the environment has been widely studied since the 1950s, both through laboratory experiments and, more recently, through field observations (e.g., Cline, 1953; Kirchmann et al., 1979; Daillant et al., 2004; McCubbin et al., 2001; Kim et al., 2012). In its "free" forms, [i.e. 3H gas or 3H hydride (HT); methyl 3H gas (CH3T); tritiated H2O or 3H-oxide (HTO); and Tissue Free Water 3H (TFWT)], tritium closely follows the water cycle. However, 3H bound with organic compounds, mainly during the basic stages of photosynthesis or through weak hydrogen links, is less exchangeable with water, which explains its persistence in the carbon cycle as re underlined recently by Baglan et al. (2013), Jean-Batiste and Fourré (2013), Kim et al. (2013a,b). In this paper, we demonstrate that terrestrial biomass pools, historically contaminated by global atmospheric fallout from nuclear testing, have constituted a significant delayed source of organically bound tritium (OBT) for aquatic systems, resulting in an apparent enrichment of OBT as compared to HTO. This finding helps to explain concentration factors (tritium concentration in biota/concentration in water) greater than 1 observed in areas that are not directly affected by industrial radioactive wastes, and thus sheds light on the controversies regarding tritium 'bioaccumulation'. Such apparent enrichment of OBT is expected to be more pronounced in the Northern Hemisphere where fallout was most significant, depending on the nature and biodegradability of terrestrial biomass at the regional scale. We further believe that OBT transfers from the continent to oceans have been sufficient to affect tritium concentrations in coastal marine biota (i.e., near river inputs). Our findings demonstrate that the persistence of terrestrial organic (3)H explains imbalances between organically bound tritium and free (3)H in most river systems in particular those not impacted by releases from nuclear facilities.

Differential biomagnification of PCB, PBDE, Hg and Radiocesium in the food web of the European hake from the NW Mediterranean.

Consumption of marine organisms represents one of the main exposure sources of contaminants for human populations. To obtain a global view of the contamination in commercial fish in the NW Mediterranean Sea, we analysed four types of priority contaminants (PCBs, PBDEs, Hg and (137)Cs) in the European hake, Merluccius merluccius, from the Gulf of Lions in relation with organism's trophic level (δ(15)N). All contaminants presented a significant increase in concentration in hake muscle with trophic level. However, obvious differences between contaminants were evidenced. Biomagnification factors (BMF and FWMF) along the hake food web were higher for Hg and CB-153 than for BDE-47 and (137)Cs, and increase in contaminant concentration with trophic level occurred at different rates depending on contaminants. Such differences of biomagnification patterns can be related to physico-chemical properties of the different contaminants.

(210)Po and (210)Pb in the tissues of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen field (Mid-Atlantic Ridge).

The hydrothermal deep-sea vent fauna is naturally exposed to a highly specific environment enriched in potentially toxic species such as sulfides, metals and natural radionuclides due to the convective seawater circulation inside the oceanic crust and its interaction with basaltic or ultramafic host rocks. However, data on radionuclides in biota from such environment are very limited. An investigation was carried out on tissue partitioning of (210)Po and (210)Pb, two natural radionuclides within the (238)U decay chain, in Bathymodiolus azoricus specimens from the Mid-Atlantic Ridge (Menez Gwen field). These two elements showed different distributions with high (210)Pb levels in gills and high (210)Po levels in both gills and especially in the remaining parts of the body tissue (including the digestive gland). Various factors that may explain such partitioning are discussed. However, (210)Po levels encountered in B. azoricus were not exceptionally high, leading to weighted internal dose rate in the range 3 to 4 µGy h⁻¹. These levels are slightly higher than levels characterizing coastal mussels (~1 µGy h⁻¹).

High levels of natural radioactivity in biota from deep-sea hydrothermal vents: a preliminary communication.

Hydrothermal deep-sea vent fauna is naturally exposed to a peculiar environment enriched in potentially toxic species such as sulphides, heavy metals and natural radionuclides. It is now well established that some of the organisms present in such an environment accumulate metals during their lifespan. Though only few radionuclide measurements are available, it seems likely that hydrothermal vent communities are exposed to high natural radiation doses. Various archived biological samples collected on the East Pacific Rise and the Mid-Atlantic Ridge in 1996, 2001 and 2002 were analysed by ICP-MS in order to determine their uranium contents ((238)U, (235)U and (234)U). In addition (210)Po-Pb were determined in 2 samples collected in 2002. Vent organisms are characterized by high U, and Po-Pb levels compared to what is generally encountered in organisms from outside hydrothermal vent ecosystems. Though the number of data is low, the results reveal various trends in relation to the site, the location within the mixing zone and/or the organisms' trophic regime.

Plutonium isotopes in the lower reaches of the River Rhône over the period 1945-2000: fluxes towards the Mediterranean Sea and sedimentary inventories.

Plutonium isotopes in the Rhône River originate from both the weathering of the catchment basin contaminated by global atmospheric fallout, and the liquid effluents released from the Marcoule reprocessing plant since 1961. Due to a new treatment process applied to the liquid effluents, a decrease of two orders of magnitude in the industrial plutonium discharged into the River Rhône has been registered from 1991. Today, 238Pu industrial inputs to the River Rhône are still about 10 times higher than those derived from global fallout, while 239+240Pu inputs from industrial and global fallout sources are of similar importance, i.e. 1 GBq y(-1). Our results indicate that the river sedimentary compartment act either as a sink or a delayed-source term of plutonium for the freshwaters depending on the hydraulic regime and flood events. This compartment may then represent an important industrial delayed-source term for the River Rhône freshwaters in the coming years as the Marcoule reprocessing plant is being dismantled. These results were obtained from samples collected from the lower course of the River Rhône over the 1987-1998 period and analysed for 238Pu and 239+240Pu activities. Both river sedimentary inventories of plutonium isotopes and effective outputs from the River Rhône towards the Gulf of Lions have been estimated for each year over the 1945-2000 period. Regarding 239+240Pu, the sedimentary inventory accumulated since 1945 is estimated to be 172+/-35 GBq. If mobile, this amount represents a significant delayed-source term of plutonium on the scale of the Rhône watershed.

Importance of colloids in the transport within the dissolved phase (<450 nm) of artificial radionuclides from the Rhône river towards the Gulf of Lions (Mediterranean Sea).

The significance of colloidal fractions regarding the transport of artificial radionuclides in natural water systems is underlined by using sequential ultrafiltration both in the Rhône freshwater and the marine area under and outside the influence of the river outflow. Indeed, the Rhodanian aquatic system represents an interesting test site as various artificial radionuclides are released into the Rhône river by several nuclear installations. We focused our study on (137)Cs, (106)Ru, (60)Co, (238)Pu and (239+240)Pu. Our results show that Fe, Al and Organic carbon (OC) are the main components of colloidal matter. Colloids represent about 15% of dissolved (<450 nm) OC and 25% of dissolved Fe and Al exported towards the sea. Within the dissolved (< 450 nm) phase, these colloidal compounds are shown to account for the transport of 40% for both Co and Ru, 60% for (238)Pu and (239+240)Pu and have no significance on (137)Cs flux.