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

C Aquatic systems Background levels Global fallout Regional scale a b s t r a c t 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 e2012) 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

In search of the authentic nation: landscape and national identity in Canada and Switzerland

While the study of nationalism and national identity has flourished in the last decade, little attention has been devoted to the conditions under which natural environments acquire significance in definitions of nationhood. This article examines the identity-forming role of landscape depictions in two polyethnic nation-states: Canada and Switzerland. Two types of geographical national identity are identified. The first – what we call the ‘nationalisation of nature’– portrays zarticular landscapes as expressions of national authenticity. The second pattern – what we refer to as the ‘naturalisation of the nation’– rests upon a notion of geographical determinism that depicts specific landscapes as forces capable of determining national identity. The authors offer two reasons why the second pattern came to prevail in the cases under consideration: (1) the affinity between wild landscape and the Romantic ideal of pure, rugged nature, and (2) a divergence between the nationalist ideal of ethnic homogeneity and the polyethnic composition of the two societies under consideration

Spatial and temporal variation of tritium concentrations during a dam flushing operation

International audienceTritium is a radionuclide commonly observed worldwide in riverine systems. In the Rhône River downstream the Lake Geneva (Switzerland and France), its occurrence is also related to its use for its luminescent properties in watchmaking paints. In fact, tritium is regularly observed at anomalous levels in this river and extreme events such as flushing operations might conduct to its transport downstream. In the Rhône River, characterized by 21 dams downstream the Geneva Lake, such operations are regularly organized to remove the sediments and limit problematic consequences such as siltation and increased flooding hazards. The consequences of dam flushing operations on tritium concentrations were thus investigated. Samples of Suspended Particulate Matter (SPM) and water were collected in the Rhone River downstream of Geneva in June 2012, during a planned flushing operation of three upstream reservoirs (Verbois, Chancy-Pougny and Génissiat). The concentrations of tritiated water (HTO) and organically bound Tritium (OBT) were measured and compared to reference concentrations. The flushing operations had no impact on the HTO concentration while the increases observed were related to the authorized releases of HTO from a nuclear power plant located downstream the dams. High increases of OBT concentrations were observed at two stations (Creys-Malville and Jons) without clear spatial or temporal trends. Since similarly high OBT concentrations had already been observed in suspended and deposited sediments during normal flow condition, these anomalous peaks could be explained by the heterogeneous spatial distribution of OBT in sediment sources that were resuspended during the flushing operations. The results highlight the need to investigate the amount of OBT currently stored in the upstream Rhone River as it might be significant

Characterizing the main sources of radiocesium using 135Cs/137Cs ratio

International audienceSeveral decades after the releases, man-made 137Cs still occurs in both the terrestrial and aquatic environments. Such a persistance is not only due to the radioactive period of this radionuclide (halflife = 30.08 y), but also to its strong retention by the clay minerals which makes radiocesium ubiquoulsy present in both the soils and the sediments. While the isotopic signatures of the actinides (e.g., uranium and plutonium) have been used successfully to distinguish the contributions of various sources of nuclides, radiocesium isotopic fingerprint has not yet been applied routinely for source identification. In the current work it is assumed that each anthropogenic source of 137Cs ischaracterized by a specific 135Cs/137Cs ratio and thereby this latter can be used in the frame of theenvironmental monitoring programs or the studies of the transfer in the environment.Thus the present work aims at determining the cesium isotopes ratios in some environmental samples representative of the main sources of 137Cs. The determination of the signatures of the main sources is of primary importance since they constitute the end-members of the mixing equationused to determine the proportion of each source.Before any environmental analysis, a selective radiochemical protocol to separate Cs fraction from the environmental samples (such as soils and sediments) and an innovative ICP-MS/MS method for the 135Cs/137Cs ratio measurement have been developed. Then radiocesium isotopes emmited in the atmosphere by the former nuclear weapons tests and the Chernobyl accident were characterized in the soils and the sediments taken in the central part of the Pyrenees (135Cs/137Cs = 4.29 decay corrected to 2022) and in the south of the Alps (135Cs/137Cs = 0.66) respectively, assuming a long range transport of radioactive contaminations in the atmosphere before deposition with rain/snow on the both studied areas. An attempt is also made to characterizea third source, namely radiocesium isotopes routinely released by the nuclear industry by analysing sediments and aquatic vegetals taken in the Rhine river which hosts four nuclear power plants, even if two of them are now shut-down

A brief history of origins and contents of Organically Bound Tritium (OBT) and 14C in the sediments of the Rhône watershed

(IF 5.59; Q1)International audienceTritium (3H) and Carbon-14 (14C) are radionuclides of natural (cosmogenic) origin that have also been introducedinto the environment by humans since the middle of the last century. They are therefore not compoundsthat have only recently been released into the environment and they do not pose a recognized health threat dueto their lowradiotoxicity. However, they hold an important placeamong current concerns because they are beingdischarged into the environment by the nuclear industry in large quantities compared to other radionuclides.Those both radionuclides partly integrate organic matter during metabolic processes (i.e., photosynthesis) leadingto organically bound forms that can be found in sediments. Organically bound tritium(OBT) analyses carriedout on the sediments of the Rhône and its tributaries indicate a significant and historical tritiumlabelling of sedimentaryparticles all along the Rhône river, aswell as in several northern tributaries, in particular the Ognon andthe Tille rivers (tributaries of the Saone), the Doubs River and the Loue River (a tributary of the Doubs) and theArve river. The recorded levels (10 to over 20,000 Bq/L) are very likely to be related to the presence of synthetictritiated particles (technogenic tritium),whichwere used in the past inwatchmakingworkshops. Although overallcontamination levels decrease from north to south in the Rhône watershed and fade over time, particularlydue to the radioactive decay of tritium, this contamination source of technogenic tritiumin the Rhônewatershedsis currently still not negligible. Carbon-14 analyses show that the Rhône sediments generally display 14C levelsclose to the atmospheric reference values (231 Bq·kg−1 of C in 2015) or even lower in most of cases, andshow sporadic and weak labelling near nuclear facilities. The low 14C levels in the Rhône sediments are mostlikely related to the solid contributions from tributaries draining areas that are rich in fossil organic matter,and therefore devoid of 14C. In the Rhône watershed, the presence in solid particles of tritium in a form organically bound to synthetic compounds and of petrogenic (fossil) organic carbon, can potentially alter the apparentassimilation rates to the food chain of these two radionuclides

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

Tritium and 14C currently are 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 is the case with 14C (Roussel-Bebet; 2014a, 2014b, Eyrolle-Boyer et al. 2014). 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 OBT activity of sediments in pristine rivers does not significantly differ today (2007-2012) from the mean HTO content on record for rainwater (2.4±0.6 Bq/L and 1.6±0.4 Bq/L, respectively), regional differences are expected based on the biomass inventories affected by atmospheric global fallout from nuclear testings and the recycling rate of organic matter within watersheds. The results obtained between 2007 and 2012 for 14C show that the levels vary 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 organic carbon. These ranges of values overall are below the mean baseline value for the terrestrial environment (232.0±1.8 Bq/kg of C in 2012, Roussel-Debet; 2014b) in relation with dilution by carbonates and/or fossil organic carbon present in aquatic systems. This emphasises yet again the value of establishing for these two radionuclides ranges of regional baseline values in order to account for paleoclimatic and lithological variations. We also show that sedimentary archives can be used to reconstruct past 14C and OBT levels. These results have made it possible to confirm delayed contamination of aquatic sediments by atmospheric fallout from past nuclear tests, as recently demonstrated (Eyrolle-Boyer et al., 2014). Lastly, our results show that the OBT and 14C levels within the suspended particles or sediments downstream of liquid discharges from nuclear facilities are affected by inputs from tributaries, and thus by hydrology, floods origin and chronologies

Tracing the origin of suspended sediment in a large Mediterranean river by combining continuous river monitoring and measurement of artificial and natural radionuclides

International audienceDelivery of suspended sediment from large rivers to marine environments has important environmental impacts on coastal zones. In France, the Rhone River (catchment area of 98,000 km2) is by far the main supplier of sediment to the Mediterranean Sea and its annual solid discharge is largely controlled by flood events. This study investigates the relevance of alternative and original fingerprinting techniques based on the relative abundances of a series of radionuclides measured routinely at the Rhone River outlet to quantify the relative contribution of sediment supplied by the main tributaries during floods. Floods were classified according to the relative contribution of the main subcatchments (i.e., Oceanic, Cevenol, extensive Mediterranean and generalised). Between 2000 and 2012, 221 samples of suspended sediment were collected at the outlet and were shown to be representative of all flood types that occurred during the last decade. Three geogenic radionuclides (i.e., 238U, 232Th and 40K) were used as fingerprints in a multivariate mixing model in order to estimate the relative contribution of the main subcatchment sources—characterised by different lithologies—in sediment samples collected at the outlet. Results showed that total sediment supply originating from Pre-Alpine, Upstream, and Cevenol sources amounted to 10, 7 and 2.10^6 tons, respectively. These results highlight the role of Pre-Alpine tributaries as the main sediment supplier (53%) to the Rhone River during floods. Other fingerprinting approaches based on artificial radionuclide activity ratios (i.e., 137Cs/239 + 240Pu and 238Pu/239 + 240Pu) were tested and provided a way to quantify sediment remobilisation or the relative contributions of the southern tributaries. In the future, fingerprinting methods based on natural radionuclides should be further applied to catchments with heterogeneous lithologies. Methods based on artificial radionuclides should be further applied to catchments characterised by heterogeneous post-Chernobyl 137Cs deposition or by specific releases of radioactive effluents

Trajectories of technogenic tritium in the Rhône River (France)

International audienceTritium is a radioisotope of hydrogen with a half-life of 12.32 years and was used for its luminescent properties by the watchmaking industry from 1962 to the 2008. Tritiated luminescent salts were integrated in the paints applied on the index and dial of watches and clocks. French and Swiss watchmaking workshops used more than 28 000 TBq of tritium over this period of time and produced almost 350 million watches. Despite the end of tritiated salts use in watchmaking workshops in 1992 in France and 2008 in Switzerland, high level of organically bound tritium (OBT) are still observed in sediments of the Rhône River downstream the Lake Geneva. Contamination of the Rhône River by tritiated hot particles since 1962 up to nowadays remains poorly documented. In order to assess the long term behavior and fate of technogenic tritium in this river and its trajectories in the river system, two sediment cores were collected at the upstream (UC) and downstream (DC) part of the Rhône River in France and OBT contents were determined. For both sedimentary cores, maximum OBT contents were registered over the 1980s when tritium was intensively used by watchmaking industries. These residual OBT contents are 1 000 to 10 000 fold higher than current natural background levels in riverine sediments. The OBT contents progressively decreased since 1989 with close effective half-life in upstream and downstream area (5 ± 2 years). The OBT contents were lower in DC than in UC due to the dilution by uncontaminated sediments delivered by tributaries not affected by the watchmaking industries. Trajectories analysis indicates that the resiliency of the Rhône River system in regards to this contamination would be reached in 14 to 70 years and in 14 to 28 years respectively for the upstream and downstream part of the river

Cultiver la ville

L’action de cultiver la ville, dont le renouveau est perceptible ces dernières années dans les villes du Nord comme dans celles des Suds, sous des formes multiples, s’inscrit dans une démarche de contes­tation des modèles de développement dominants. Elle se traduit par de nouvelles pratiques de la ville et par des formes originales d’appropriation de leur environnement par les citadins. Ainsi « l’agrarisation » de la ville, en renouvelant les modes de produire, de consommer et de vivre ensemble, dans un cadre de vie préservé, s’intègre dans une démarche que l’on peut qualifier de transition environnementale. Au-delà, en contribuant à réintroduire un peu de « nature » dans des quartiers d’où elle en était exclue, le jardinage s’inscrit dans la recherche d’une plus grande justice environnementale. Cultiver la ville participe par ailleurs de la transition vers des systèmes alimentaires plus durables et mobilise le concept de justice alimentaire. Quelle que soit sa forme, l’action de cultiver la ville, est associée à un mouvement social producteur de dynamiques territoriales spécifiques. (Re)conquête d’espaces délaissés ou marginalisés, réappro­priation d’un cadre de vie, lutte pour une plus grande justice environnementale et/ou alimentaire, participation active à la construction d’un projet territorial et/ou patrimonial… : ce numéro se pro­pose d’explorer ici et ailleurs un certain nombre de démarches citoyennes territorialisées qui s’appuient sur diverses formes de cultiver la ville