Aquatic Toxicology 169 (2015) 10–18 Contents lists available at ScienceDirect Aquatic Toxicology j o ur na l ho me pag e: www.elsevier.com/locate/aquatox Tissue specific responses to cadmium-based quantum dots in the marine mussel Mytilus galloprovincialis Thiago Lopes Rocha a , Tânia Gomes a,b , Nélia C. Mestre a , Cátia Cardoso a , Maria João Bebianno a,∗ a CIMA, Faculty of Science and Technology, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal b Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, NO-0349 Oslo, Norway a r t i c l e i n f o Article history: Received 7 July 2015 Received in revised form 8 September 2015 Accepted 2 October 2015 Available online 8 October 2015 Keywords: Nanomaterials Metal-based nanoparticle CdTe quantum dots Ecotoxicology Oxidative stress a b s t r a c t In recent years, Cd-based quantum dots (QDs) have generated interest from the life sciences community due to their potential applications in nanomedicine, biology and electronics. However, these engineered nanomaterials can be released into the marine environment, where their environmental health haz- ards remain unclear. This study investigated the tissue-specific responses related to alterations in the antioxidant defense system induced by CdTe QDs, in comparison with its dissolved counterpart, using the marine mussel Mytilus galloprovincialis. Mussels were exposed to CdTe QDs and dissolved Cd for 14 days at 10 gCd L −1 and biomarkers of oxidative stress [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (total, Se-independent and Se-dependent GPx) and glutathione-S-transferase (GST) activities] were analyzed along with Cd accumulation in the gills and digestive gland of mussels. Results show that both Cd forms changed mussels’ antioxidant responses with distinct modes of action (MoA). There were tissue- and time-dependent differences in the biochemical responses to each Cd form, wherein QDs are more pro-oxidant when compared to dissolved Cd. The gills are the main tissue affected by QDs, with effects related to the increase of SOD, GST and GPx activities, while those of dissolved Cd was associated to the increase of CAT activity, Cd accumulation and exposure time. Digestive gland is a main tissue for accumulation of both Cd forms, but changes in antioxidant enzyme activities are smaller than in gills. A multivariate analysis revealed that the antioxidant patterns are tissue dependent, indicating nano-specific effects possibly associated to oxidative stress and changes in redox homeostasis. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Quantum dots (QDs) are engineered semiconductor nanocrys- tals with a nanometer diameter (2–10 nm) comprising a metalloid core usually coated with a shell or ligands, which enhances its optical and electronic properties while reducing metal leaching. Cd-based QDs have been used in different nanotechnologies includ- ing biomedical imaging, cancer detection, targeted drug delivery, electronics, pharmacy and as chemosensors in analytical chem- istry (Michalet et al., 2005; Rizvi et al., 2010). The increasing production and use of these engineered nanoparticles (ENPs) will likely increase their release into the aquatic environment. Although QDs concentrations in the environment are unavailable, there are increasing concerns about their possible ecological risks and toxi- city to human health (Hardman, 2006; Rocha et al., 2014, 2015a). ∗ Corresponding author. Fax: +351 289800069. E-mail address: mbebian@ualg.pt (M.J. Bebianno). Ecotoxicological impact of Cd-based QDs in aquatic organisms has been reported in several studies using in vitro and in vivo expo- sure (Gagné et al., 2008a; Peyrot et al., 2009; Katsumiti et al., 2014; Rocha et al., 2014,2015a; Buffet et al., 2015). However, the mecha- nisms of QD-mediated toxicity are not well established and depend on size, chemical composition, surface coating and exposure con- ditions. Many studies suggest that the QD toxicity is mainly related to QD dissolution and extra- and intracellular release of Cd 2+ ions (Peyrot et al., 2009; Domingos et al., 2011; Katsumiti et al., 2014). On the other hand, other studies indicate that the generation of free radicals or reactive oxygen species (ROS) associated with oxida- tive damage are the major mode of action (MoA) of Cd-based QDs (Gagné et al., 2008a; Buffet et al., 2015). QDs are efficient energy donors and have the ability to generate ROS in aqueous solutions under exposure to ultraviolet or visi- ble electromagnetic radiation (Ipe et al., 2005). In this condition, QDs can promote the delocalization of an electron (e − ) from the valence band (v b ) to conduction band (c b ) creating an electron–hole pair (e cb − + h vc + ), which can undergo redox reactions with surface http://dx.doi.org/10.1016/j.aquatox.2015.10.001 0166-445X/© 2015 Elsevier B.V. All rights reserved.