Gene expression changes and toxicity of selected rare earth elements in rainbow trout juveniles

Rare earth elements (REEs) are increasingly used in electronics industry and other areas of our economy and questions were raised about their impacts to the environment. The purpose of this study was to examine the lethal and sublethal toxicity of REEs in juvenile rainbow (Oncorhynchus mykiss) trout. The fish were exposed to increasing concentrations (0.064, 0.32, 1.6, 8 and 40 mg/L) of the following 7 REEs for 96 h at 15 °C: cerium (CeCl₃), erbium (ErCl₃), gadolinium (GdCl₃), lanthanum (LaCl₃), neodymium (NdCl₃), samarium (SmCl₃) and yttrium (YCl₃). The mortality were determined and in the surviving fish, 10 target gene transcripts were measured in the liver to track changes in oxidative stress, DNA repair, tissue growth/proliferation, protein chaperoning, xenobiotic biotransformation and ammonia metabolism. The data revealed that Y, Sm, Er and Gd formed a distinct group based on toxicity (mortality) and gene expression changes. Electronegativity was significantly correlated (r = -0.8, p < 0.01) with the lethal concentration (LC50). Gene expression changes occurred at concentration circa 120 times lower than the LC50 and the following transcripts in protein chaperoning (heat shock proteins), DNA repair (growth arrest DNA Damage) and CYP1A1 gene expression involved in the metabolism of coplanar aromatic hydrocarbons were involved. In conclusion, the study revealed that the more electronegative REEs were the most toxic to trout juveniles and produced sublethal effects at concentrations 2 orders of magnitude lower than the lethal concentrations. The toxicity of REEs depends on the elements were toxicity involves specific pathways at the gene expression level.