Variations of anthropogenic gadolinium in rivers close to waste water treatment plant discharges.

Rare earth element (REE) concentrations were determined for 22 sites sampled during two water periods: high flow in winter and low flow in summer. Shale-normalized REE patterns of all samples displayed positive gadolinium (Gd) anomalies. They revealed a widespread contamination of anthropogenic Gd (Gdant) from waste water treatment plant (WWTP) outputs to catchment areas used for drinking water. No significant variations in Gdant were observed between the two flow water periods, but differences in the Gd anomalies were present. However, these differences seem to be associated rather with seasonal variations in the river flow rate than with the release of GdAnt from WWTPs. In proximity to WWTP discharges, strong GdAnt variations ranged from few nanograms per litre to more than 80 µg L-1 and rarely showed a repetitive pattern day after day during 14 days. These concentrations were diluted into the river stream and measured around 10 ng L-1 close to the catchment areas used for drinking water. A principal component analysis (PCA) using the GdAnt concentrations and some classical physicochemical parameters (pH, water temperature, total alkalinity (TA), total organic carbon (TOC), biochemical and chemical oxygen demand (BOD and COD), Cl-, NO3- and SO42-) allowed a site separation according to the level of Gd contamination, highlighting that the highest GdAnt concentrations were found in the north of the region Lorraine (France) where the population density is high and most of the MRI examinations are performed.

Bioaccumulation of gadolinium in freshwater bivalves.

In this study, the presence of anthropogenic gadolinium (Gd) was evaluated in rivers, close to wastewater treatment plant outputs. Then, one site was selected for in situ experiments to assess the bioaccumulation of Gd in the digestive gland and in the gills of two bivalves (Dreissena rostriformis bugensis and Corbicula fluminea). For both organisms, the results suggested that the bioaccumulation of Gd can be observed when organisms are exposed in a geogenic and anthropogenic Gd mixture. In order to observe if Gd can bioaccumulate in tissues of bivalves when the ion is only present as the main anthropogenic speciation of Gd, i.e., Gd-contrast agents (Gd-CAs), the gadoteric acid was used for a laboratory experiment. In this case, the presence of Gd was clearly detected in a significant amount in the digestive glands of D. rostriformis bugensis and C. fluminea while low concentrations are measured in the gills. For the first time, these results clearly showed that Gd can bioaccumulate in bivalve tissues even when it is only present as Gd-CAs. Biochemical activities were measured in the digestive gland and in the gills of the bivalves to assess the effects of Gd-CA bioaccumulation. No significant variations were observed in the gills. Concerning the digestive gland, after 7 days of exposure at 10 µg L-1 of Gd as Gd-CA speciation, GST activity in D. rostriformis bugensis and lipid hydroperoxide and mitochondrial electron transfer system in C. fluminea had increased. The results suggest an acclimation of the organisms to the presence of Gd-CAs in the medium within less than 21 days.