Toxicity of representative mixture of five rare earth elements in juvenile rainbow trout ( Oncorhynchus mykiss) juveniles

Rare earth elements (REEs) are contaminants of increasing interest due to intense mining activities for commercial purposes and ultimately released in the environment. We exposed juvenile rainbow trout (Oncorhynchus mykiss) to a representative mixture of the five most abundant REEs for 96 h at concentrations similar found in lakes contaminated by mining activities at 0.1, 1, 10, and 100X whereas the 1x mixture contained cerium (Ce, 280 μg/L), lanthanum (La, 140 μg/L), neodymium (Nd, 120 μg/L), praseodymium (Pr, 28 μg/L), and samarium (Sm, 23 μg/L). We investigated the expression of 14 genes involved in oxidative stress, DNA repair, tissue growth/proliferation, protein chaperoning, xenobiotic biotransformation, and ammonia metabolism in the liver. In addition, DNA damage, oxidative stress (lipid peroxidation or LPO), inflammation (cyclooxygenase or COX activity), detoxification mechanisms (glutathione-S-transferase activity or GST), and labile zinc were determined in gills. The data revealed that genes involved in oxidative stress-catalase (cat), heat shock proteins 70 (hsp70), and glutamate dehydrogenase (glud) were upregulated while glutathione S-transferase (gst) and metallothionein (mt) gene expressions were downregulated. The mixture was genotoxic and increased labile Zn in gills of exposed trout. These changes occurred at concentrations 600 times lower than the LC50 for this mixture indicating effects below the 1X concentration. Based on principal component analysis and concentration-dependent reponses, the following sublethal effects were considered the most important/significant: DNA strand breaks (genotoxicity), labile Zn, cat, gst, hsp70, sparc, mt, and glud. These effects of fish juveniles are likely to occur in environments under the influence of mining activities.