Abstract
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.
Highlights
Rare earth elements (REEs) comprise the 15 elements of the lanthanide family in addition to scandium and yttrium
We evaluated genotoxicity (DNA strand breaks), mRNA expression of a set of genes involved in oxidative stress, Fe3+ /divalent metal homeostatis, DNA repair, protein denaturation, cell growth/ proliferation and intermediary metabolism and biochemical markers of oxidative stress, inflammation, detoxification mechanisms, and labile zinc, which is a biomarker for metal exposure, in the gills and liver
The reported LC50 for the single REEs was included and revealed that Sm concentration in the mixture (1.36 mg/L) corresponded to the LC50 of Sm alone (1.6 mg/L) suggesting that toxicity was mainly samarium-driven in this mixture
Summary
Rare earth elements (REEs) comprise the 15 elements of the lanthanide family in addition to scandium and yttrium Demand for these chemicals is increasing, as they are essential for a number of technological products including smartphones and miscellaneous computer parts. REEs are considered contaminants of emerging interest, as mining efforts and subsequent release into the aquatic environment raise concerns about the ecotoxicological impacts to the aquatic environment This group of chemicals has already been detected in the marine (Moermond et al 2001), freshwater (Kulaksiz and Bau 2011), and soil environment (Tranchida et al 2011) as well as biota (Tu et al 1994; Bustamante and Miramand 2005; Hu et al 2006; Censi et al 2013; Fu et al 2014; Mayfield and Fairbrother 2015). Information on potential adverse toxicological effects and toxicity mechanisms is still scarce to date for this group of elements
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