Trajectories of technogenic tritium in the Rhône River (France).

Tritium 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 14-70 years and in 14-28 years respectively for the upstream and downstream part of the river.

Bioaccessibility of polycyclic aromatic compounds (PAHs, PCBs) and trace elements: Influencing factors and determination in a river sediment core.

Organic matter (OM), clays, sand or time are factors possibly influencing the bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) from sediments. An experimental design was performed to monitor and quantify this process. The bioaccessible fraction, linked to the rapidly-desorbing fraction (Frap) of contaminants, was assessed through a non-exhaustive extraction using a carboxymethyl-ß-cyclodextrin polymer. OM content was the most influential factor as regards Frap. Clay percentage was a slightly influential factor for PAHs while the interaction sand × OM was a slightly influential factor for PCBs. Frap was also determined in a sediment core collected from Martot's Pond (France). The higher the PAH/PCB concentration in this sediment, the higher the bioaccessible fraction. The relationship between a lower bioaccessibility and a higher number of PAHs cycles or PCB chlorines was linear. OM content impacted on Frap only for PAHs. Sequential extractions of some trace elements were also performed to evaluate their mobility. Cu, Cr, Pb, Ni were the less bioaccessible. A great part of As, Cd and Zn was found in the most bioaccessible sediment fractions. The 40-65 cm section might be considered as the most negatively impacting on the aquatic fauna, due to Cd and Zn high bioaccessible concentrations.

Combined spatial and retrospective analysis of fluoroalkyl chemicals in fluvial sediments reveal changes in levels and patterns over the last 40 years.

Bed sediments and a dated sediment core were collected upstream and downstream from the city of Lyon (France) to assess the spatial and temporal trends of contamination by per- and polyfluoroalkyl substances (PFASs) in this section of the Rhône River. Upstream from Lyon, concentrations of total PFASs (ΣPFASs) in sediments are low (between 0.19 and 2.6 ng g-1 dry weight - dw), being characterized by a high proportion of perfluorooctane sulfonate (PFOS). Downstream from Lyon, and also from a fluoropolymer manufacturing plant, ΣPFASs concentrations reach 48.7 ng g-1 dw. A gradual decrease of concentrations is reported at the coring site further downstream (38 km). Based on a dated sediment core, the temporal evolution of PFASs is reconstructed from 1984 to 2013. Prior to 1987, ΣPFASs concentrations were low (≤2 ng g-1 dw), increasing to a maximum of 51 ng g-1 dw in the 1990s and then decreasing from 2002 to the present day (∼10 ng g-1 dw). In terms of the PFAS pattern, the proportion of perfluoroalkyl sulfonic acids (PFSAs) has remained stable since the 1980s (∼10%), whereas large variations are reported for carboxylic acids (PFCAs). Long chain- (C > 8) PFCAs characterized by an even number of perfluorinated carbons represent about 74% of the total PFAS load until 2005. However, from 2005 to 2013, the relative contribution of long chain- (C > 8) PFCAs with an odd number of perfluorinated carbons reaches 80%. Such changes in the PFAS pattern likely highlight a major shift in the industrial production process. This spatial and retrospective study provides valuable insights into the long-term contamination patterns of PFAS chemicals in river basins impacted by both urban and industrial activities.