Tritium and radiocarbon levels in the Rhône river delta and along the French Mediterranean coastline.

The Rhône is characterised by a heavy concentration of nuclear-based industries including nuclear power stations and nuclear sites housing civilian and military facilities. Here, we report the results of a four-year survey (2010-2013) of tritium and radiocarbon levels in a variety of matrices within the Rhône delta and along the French Mediterranean coastline. The aim of the study is to create a spatial reference framework of environmental levels of these two radionuclides, which are the most prevalent in radioactive effluents from nuclear power stations. Although both tritium and radiocarbon levels in the samples analysed are very low and can only be detected using ultra-sensitive analytical techniques, they clearly show the influence of the tritium and radiocarbon discharges carried by the Rhône plume along the Mediterranean coast. The tritium content of suspended matter and sediments of the Rhône is a special case, which shows elevated tritium values not seen in other French rivers with similar nuclear facilities. The north-south spatial distribution of this tritium anomaly shows that these trace values are at their highest in the upper Rhône, close to the Swiss border and upstream of Creys Malville, the northernmost nuclear power station on the Rhône. This points to a legacy of past tritium releases by the watchmaking industry. A dedicated study would be needed to clearly identify the source and the exact nature of this contamination.

Modelling tritium flux from water to atmosphere: application to the Loire River.

Tritium (³H or T) is one of the major radionuclides released by nuclear power plants (NPP) into rivers. However, tritiated water (HTO) flux from water to air is seldom considered when assessing health effects of such releases. The aim of this paper is to present the result of a research program, called LORA, conducted on the Loire River (France). To improve our understanding of HTO flux from surface water to air, three field campaigns were organised during the NPP's radioactive releases to measure simultaneously the activity concentrations in air on the riverbank, using an innovative system, and in river water. The measurements showed that during radioactive releases, water vapour was enriched in ³H. These results were used to calibrate exchange velocities. The average of these estimated exchange velocities was more than one order of magnitude higher than those calculated in the literature from indoor experiments. The variability of these values was also larger, showing that outdoor studies cover a wide range of conditions influencing HTO flux. No correlation was observed between exchanges velocities and meteorological conditions. However, there was a significant difference between day and night with a higher value observed during the day. Two approaches used to calculate HTO evaporation from water (i.e. the approach based on water evaporation and the approach considering that HTO follows its own concentration gradient) were included in a hydrodynamic model, which was used to evaluate HTO air activity along the Loire River. In conclusion, only the approach considering that HTO follows its own gradient led to a good agreement between measurements and predictions. A one-year simulation was done to estimate the contribution of this process to the dose. Its contribution can be considered as negligible in this case compared to the other pathways such as ingestion of water or foodstuffs.

Carbon isotope ratio monitoring-gas chromatography mass spectrometric measurements in the marine environment: biomarker sources and paleoclimate applications.

Some applications in the use of compound-specific isotopic analyses (CSIA) for biomarker source elucidation in the marine environment and its potential applications to paleoclimatology are evaluated in the present study. The potential use of the carbon isotope ratios of marine biomarkers as recorders of CO2 levels has been considered. A significant correlation between delta 13C cholesterol of suspended particulates and seawater CO2 concentrations from the south Indian Ocean has been found. delta 13C composition in biomarkers of different functionalities from three photosynthetic organisms has been examined. Small variations within and between biosynthetically related compound classes have been observed in cyanobacteria. In algae, e.g. diatoms and dinoflagellates, significant differences between the average delta 13C composition of fatty acids and sterols were observed (7.5/1000 and 2/1000, respectively). These differences can be attributed to diverse isotope effects associated with different biosynthetic reactions. Isotopic variations among homologues of the same lipid class have also been observed. In diatoms, variations were up to 5/1000 within each class of fatty acids and sterols and in the dinoflagellate species, these variations were lower than 3/1000. These differences, and particularly the intra-specific shifts in delta 13C lipid composition, must be considered for the correct interpretation of changes in delta 13C molecular signatures in the marine environment.