Antioxidant and biotransformation responses in Liza aurata under environmental mercury exposure – Relationship with mercury accumulation and implications for public health S. Guilherme a, * , M. Va ´lega b , M.E. Pereira b , M.A. Santos a , M. Pacheco a a CESAM and Biology Department, Aveiro University, Campus de Santiago, 3810-193 Aveiro, Portugal b CESAM and Chemistry Department, Aveiro University, Campus de Santiago, 3810-193 Aveiro, Portugal Abstract This study was carried out in the Laranjo basin (Ria de Aveiro, Portugal), an area impacted by mercury discharges. Liza aurata oxi- dative stress and biotransformation responses were assessed in the liver and related to total mercury (Hg t ) concentrations. A seasonal fish survey revealed a sporadic increase in total glutathione (GSH t ) and elevated muscle Hg t levels, although Hg levels did not exceed the EU regulatory limit. As a complement study, fish were caged for three days both close to the bottom and on the water surface at three loca- tions, and displayed higher Hg t levels accompanied by increased GSH t content and catalase activity as well as EROD activity inhibition. The bottom group displayed higher hepatic Hg t and GSH t contents compared with the surface group. Globally, both wild and caged fish revealed that the liver accumulates higher Hg t concentrations than muscle and, thus, better reflects environmental contamination levels. The absence of peroxidative damage in the liver can be attributed to effective detoxification and antioxidant defense. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Oxidative stress; Biotransformation; Mercury; Liza sp.; Ria de Aveiro (Portugal) 1. Introduction Mercury is a toxic and hazardous metal that occurs nat- urally in the earth’s crust. Natural phenomena such as ero- sion and volcanic eruptions, as well as anthropogenic activities may lead to substantial contamination of the environment (Tchounwou et al., 2003). Increasing loads of mercury in the aquatic environment have resulted in greater accumulation of this metal in the tissues of fish and fish consumers (Gilbertson and Carpenter, 2004). Fish populations can be adversely affected by the pres- ence of mercury within their tissues, making it important to assess its distribution and subsequent retention. Mer- cury quantifications in tissues are, generally, the best way to gain a better understanding of the dynamics of this con- taminant in the fish body. The liver is targeted due to its role in detoxification and importance to individual fish health (Cizdziel et al., 2003). The mercury residue in fish muscle, which is recognized as the major route of human mercury exposure (Tchounwou et al., 2003), is mainly the most toxic form – methylmercury (MeHg). Despite numer- ous studies examining mercury quantification in fish tis- sues, scientific knowledge of the relationship between these levels and their effects on fish health remain scarce. Fish studies have demonstrated that antioxidant systems could provide relevant indices in explaining the sensitivity of some fish species to contaminants (Di Giulio et al., 1993; Lemaire and Livingstone, 1993). Antioxidants play a crucial role in maintaining cell homeostasis and, when these defenses are impaired or surmounted, oxidative stress products, namely reactive oxygen species (ROS), may induce DNA damage, enzymatic inactivation and peroxi- dation of cell constituents. To prevent damage caused by ROS, fish usually cope by increasing the levels of protective antioxidants enzymes, namely catalase (CAT), glutathione 0025-326X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2008.02.003 * Corresponding author. Tel.: +351 96 64 69 474. E-mail address: sofiaguilherme@bio.ua.pt (S. Guilherme). www.elsevier.com/locate/marpolbul Available online at www.sciencedirect.com Marine Pollution Bulletin 56 (2008) 845–859