Metal detoxification and gene expression regulation after a Cd and Zn contamination: An experimental study on Danio rerio A. Arini, P.Y. Gourves, P. Gonzalez, M. Baudrimont ⇑ University of Bordeaux 1, Laboratoire d’Ecotoxicologie Aquatique, UMR CNRS 5805, Place du Dr. Peyneau, Arcachon 33120, France highlights  This study aimed to demonstrate the recovery potential of Danio rerio after Cd and Zn contaminations.  The 75-day decontamination failed to completely eliminate Cd whereas Zn was quickly depurated.  Cd induced over-expressions of genes involved in detoxification and against oxidative stress.  Zn binary contamination with Cd provided protective effects on Cd-induced toxicity in Danio rerio.  After 14–30 d of depuration, genes were no longer over expressed in response to Cd. article info Article history: Received 23 July 2014 Received in revised form 9 January 2015 Accepted 14 January 2015 Handling Editor: A. Gies Keywords: Depuration Cadmium Zinc Metallothionein Gene expression Danio rerio abstract This study aimed to demonstrate the recovery potential of Danio rerio after Cd and Zn contaminations. Fish demonstrated high accumulation capacities of Cd with concentrations reaching 3716.4 ± 578.6 lg Cd/kg FW in gills after 15 d of contamination. The 75-day decontamination failed to completely eliminate Cd (93.4% and 82.2% eliminated respectively in the gills of fish exposed to Cd and Cd/Zn) whereas Zn, poorly accumulated, was quickly depurated. The fast Cd depuration in the gills likely resulted from a metal transfer to the liver. MT response was clearly correlated to the Zn contamination, while genetic responses were more pronounced in case of Cd contamination. Cd induced over-expressions of genes involved against oxidative stress (sod, sodmt), and involved in detoxification mechanisms (mt1, mt2), mitochondrial mechanisms (cox1) and DNA repair (rad51 and gadd45). Zn binary contamination with Cd was demonstrated to provide protective effects on Cd-induced toxicity in D. rerio. Results highlighted that the genetic response was metal- and tissue-dependent. The brain and the muscles showed very few genetic responses, probably due to the low bioaccumulations measured in these tissues. Conversely, genes expressed in gills and liver of fish exposed to Cd were strongly affected (sod  3 and  12, mt1  11 and 30 at T3 respectively in gills and liver). However, after 14–30 d of depuration, genes were no longer over expressed in response to Cd contamination in gills and liver of fish exposed to Cd and Cd/ Zn conditions, suggesting an gene expression regulation of fish to the residual Cd contamination. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Cadmium (Cd), a non-essential metal, is widely distributed in the environment as a result of natural and anthropogenic activities. Because of its low rate of excretion from the body, Cd exhibits long biological half-lives in aquatic organisms (Baudrimont et al., 2003; Kraemer et al., 2005; Serafim and Bebianno, 2007) and accumulates over time in several organs such as gills, liver, and kidney (Yang and Chen, 1996; De Conto Cinier et al., 1999). Cd is known for its effects at cellular level with the inhibition of the mitochondrial electron transfer chain and the induction of reactive oxygen species (ROS) (Risso-De Faverney et al., 2004; Wang et al., 2004). Metals, such as Cd and Zinc (Zn), are often present as mix- tures in aquatic environments (Wicklund Glynn, 2001). As an essential metal for life, Zn, in contrast to Cd, is a well-established antioxidant, since it is an essential component of Cu/Zn-SOD and it leads to the induction of metallothioneins (MT). This sequestra- tion protein, which provides thiol groups, is able to scavenge met- als such as Cd and also hydroxyl radicals and singlet oxygen (Dondero et al., 2005). Highlighted in the 1970s, the Riou-Mort River (South-West France) is part of hydrosystems affected by metal pollution, as by-products of Zn and lead mining. This watershed is draining a waste area of a factory previously specialized in Zn ore treatment (from 1842 to 1987). Despite a remediation process started in http://dx.doi.org/10.1016/j.chemosphere.2015.01.022 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +33 (0)556223926; fax: +33 (0)556 54 93 83. E-mail address: m.baudrimont@epoc.u-bordeaux1.fr (M. Baudrimont). Chemosphere 128 (2015) 125–133 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere