Ecotoxicity of a Representative Urban Mixture of Rare Earth Elements to Hydra vulgaris

The aquatic toxicity of realistic mixtures of rare earth elements (REE) is less understood. The purpose of this study was to examine the sublethal and lethal toxicity of an environmentally realistic mixture of five REE in Hydra vulgaris. The REE mixture was composed of 5 elements (Gd, Ce, Nd, Yb and Dy with a total REE loading of 13.7 µg/L) that were found in 6 municipal effluents at the same concentration ratios (1X). The organisms were exposed to increasing concentrations (0.5, 1, 5, 10, 25, 50 and 100X) of the mixture for 96 h at 20oC. The lethal and sublethal toxicity was evaluated by morphological changes and the gene expression (mRNA) involved in oxidative stress, damaged protein salvaging (autophagy), regeneration, neural activity and oxidated DNA repair. The data revealed that the total REE concentration of the environmental mixture was well below the potential toxicity of REE, which occurs generally at concentrations > 200 ug/L. At the gene expression levels, effects occurred at concentrations below those reported in municipal effluents suggesting that these REEs could produce toxic effects on the long-term in hydra close to municipal effluent discharges.