Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Response of the freshwater mussel, Dreissena polymorpha to sub-lethal concentrations of samarium and yttrium after chronic exposure Houda Hanana ⁎ , Patrice Turcotte, Maxime Dubé, Christian Gagnon, François Gagné ⁎ Aquatic Contaminant Research Division, Environment and Climate Change Canada, 105 McGill, Montreal, Quebec, Canada H2Y 2E7 ARTICLE INFO Keywords: Rare earth elements Bioaccumulation Inflammation Genotoxicity Gene expression Mechanism of action ABSTRACT Samarium (Sm) and yttrium (Y) are commonly used rare earth elements (REEs) but there is a scarcity of in- formation concerning their biological effects in non-target aquatic organisms. The purpose of this study was to determine the bioavailability of those REEs and their toxicity on Dreissena polymorpha after exposure to in- creasing concentration of Sm and Y for 28 days at 15 °C. At the end of the exposure period, the gene expression of superoxide dismutase (SOD), catalase (CAT), metallothionein (MT), glutathione-S-transferase (GST), cytochrome c oxidase 1 (CO1) and cyclin D (Cyc D) were analysed. In addition, we examined lipid peroxidation (LPO), DNA strand breaks (DSB), GST and prostaglandin cyclooxygenase (COX) activities. Results showed a concentration dependent increase in the level of the REEs accumulated in the soft tissue of mussels. Both REEs decreased CAT but did not significantly modulated SOD and MT expressions. Furthermore, Sm 3+ up-regulated GST, CO1 and Cyc D, while Y 3+ increased and decreased GST and CO1 transcripts levels, respectively. Biomarker activities showed no oxidative damage as evidenced by LPO, while COX activity was decreased and DNA strand breaks levels were changed suggesting that Sm and Y exhibit anti-inflammatory and genotoxic effects. Factorial analysis revealed that the major impacted biomarkers by Sm were LPO, CAT, CO1 and COX, while GST gene expression, COX, Cyc D and CAT as the major biomarkers affected by Y. We conclude that these REEs display different mode of action but further investigations are required in order to define the exact mechanism involved in their toxicity. 1. Introduction Rare earth elements (REEs) consists of 17 elements and are classi- fied according to their ionic radii into light and heavy REEs (Fu et al., 2014). Contrary to their name, these elements are commonly found in the Earth's crust (Liang et al., 2014) and their concentrations are more abundant than those of mercury or silver (Environment Canada, 2012). This appellation refers to the lack of their concentration in pure ore deposits characteristic of other elements such as gold (Abhilash et al., 2015; Thomas et al., 2014). In the recent decades, REEs have under- gone a steady use in several industrial, medical and agriculture appli- cations (González et al., 2015; Pagano et al., 2015). Samarium (Sm) and Yttrium (Y) are among the most commonly used REEs (Chua, 1998). Y was the first REE discovered in 1794 (Hayashi et al., 2006) and is a promising element for high technology materials (Lobinger et al., 2005) such as electronic devices including television, computer, mis- cellaneous visual color displays (Rim et al., 2013), electrodes, electro- lytes, electronic filters and superconductors (Takahashi et al., 2012). However, Sm is the fifth most abundant of the REEs and is extensively used for agricultural fertilizer, magnets material synthesis and analgesic treatment for tumor patients (Zhang et al., 2014). As a consequence of industrial and agricultural practices large amounts of dissolved REEs have been discharged into the aquatic environment (Fu et al., 2014; Protano and Riccobono, 2002). It has been reported that nanomolar concentrations of the metals are usually measured in natural waters and micromolar concentrations can now be found near mining sites (Miekeley et al., 1992; Noack et al., 2014). Despite their widespread applications, there is a lack of key ecotoxicological data and only few studies have examined the long-term effects of REEs in aquatic organ- isms. Moreover, current literature on REE toxicity is mostly confined to reports on a few REE mainly Ce, La and Gd (Pagano et al., 2016). Therefore, there is a scarcity of information about the molecular in- teraction between most REEs and biological molecules in aquatic or- ganisms. Moreover, the results of toxicological studies performed with REE are controversial and the mechanisms of action and toxicity of those elements are still unknown. For this reason, monitoring of their toxicity will become crucial as REE mining activities become developed in Canada and others countries (Abhilash et al., 2015). In vivo studies on rats showed that Y exhibited cytotoxicity and promoted neuronal cell death by the induction of apoptotic pathways https://doi.org/10.1016/j.ecoenv.2018.09.047 Received 22 March 2018; Received in revised form 6 September 2018; Accepted 9 September 2018 ⁎ Corresponding authors. E-mail addresses: houda.hanana@canada.ca (H. Hanana), francois.gagne@canada.ca (F. Gagné). Ecotoxicology and Environmental Safety 165 (2018) 662–670 Available online 21 September 2018 0147-6513/ Crown Copyright © 2018 Published by Elsevier Inc. All rights reserved. T