Rapid communicationEffects of salinity on biomarker responses in Crassostrea rhizophorae (Mollusca, Bivalvia) exposed to diesel oil
Introduction
Coastal regions are frequently impacted by human exploration of natural resources. Many foreign organic and inorganic compounds may enter the marine environment through discharge of domestic sewage and industrial effluents, harbor activities, and application of biocides, deteriorating the quality of the aquatic environment. Polycyclic aromatic hydrocarbons (PAHs) are present in the marine environment due to their widespread occurrence in petroleum, coal, soot, air pollutants, and oil spillages (Walker et al., 1996), and carcinogenic properties have been associated with the exposure to these compounds (Reynaud et al., 2002).
The impact of these contaminants in biological systems can be evaluated through biomarkers related to xenobiotic biotransformation and excretion mechanisms. Biotransformation of xenobiotics may enhance the production of reactive oxygen species (ROS) and electrophilic intermediates derived from the parent chemical. These intermediates can be conjugated with endogenous molecules such as reduced glutathione (GSH) through the action of glutatione S-transferase (GST) (Livingstone, 1985). This conjugation mechanism produces more hydrophilic xenobiotics yielding expellable metabolites (Mannervik and Danielson, 1988). Cellular antioxidant defenses, such as the enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase, and free radical scavengers, such as vitamins C and E, carotenoids, and GSH among others (Stegeman et al., 1992), protect the cell against oxidative stress, inactivating the produced ROS and/or repairing oxidized biomolecules. Glucose-6-phosphate dehydrogenase (G6PDH) is a regulatory enzyme of the pentose phosphate shunt, which produces NADPH for xenobiotic biotransformation and to recycle oxidized glutathione (GSSG) to its reduced form (GSH) through a reaction catalyzed by glutathione reductase (GR). Acetylcholinesterase (AChE) is a serine hydrolase found in neuromuscular junctions that decomposes acetylcholine in the synaptic cleft (Galloway et al., 2002). AChE activity has been widely used as a biomarker of exposure to and effects of organophosphates and carbamates in aquatic organisms. Payne et al. (1996) showed that AChE is inhibited by aromatic hydrocarbons and suggested the use of the activity of this enzyme to monitor the exposure of aquatic organisms to these compounds.
The International Council for the Exploration of the Sea (ICES) has proposed the use of antioxidant and biotransformation enzymes and the inhibition of AChE as biomarkers of exposure to xenobiotics. These parameters have been studied in mussels (Livingstone et al., 1985; Le Pennec and Le Pennec, 2003) and oysters (Alves et al., 2002; Niyogi et al., 2001a). Bivalves are sessile, filter-feeding organisms found in coastal and estuarine zones, which bioaccumulate chemical compounds present in the surrounding seawater; this is the reason that they are used as sentinel organisms in biomonitoring programs (Viarengo and Canesi, 1991; Bainy et al., 2000; Cheung et al., 2001; Oliver et al., 2001; Gowland et al., 2002).
The mangrove oyster Crassostrea rhizophorae is a euryhaline osmo-conformer bivalve widely distributed along the Brazilian coast that has been proposed as a relevant biomonitor of environmental contamination in tropical systems (Nascimento et al., 1998; Wallner-Kersanach et al., 2000; Monserrat et al., 2002; Rebelo et al., 2003). They are found attached to mangrove roots and coastal rocks (Queiroz and Júnior, 1990) where drastic changes of salinity may occur, determining their distribution and affecting their structural and functional properties (Dame, 1996). Therefore, examining the effects of salinity on the toxicity of water-borne contaminants is essential in assessing the risk of exposure of estuarine organisms to these compounds (Wang et al., 2001).
The aim of this study was to assess the effects of salinity on the activities of GST, G6PDH, CAT, and AChE in digestive glands of C. rhizophorae exposed to diesel oil.
Section snippets
Animals
Mangrove oysters, C. rhizophorae (average length between 60 and 80 mm), were sampled at an oyster farming area at Sambaqui beach (Laboratório de Moluscos Marinhos, Departamento de Aquicultura, CCA, UFSC) in Florianópolis, Santa Catarina State, Brazil. The animals were collected, cleaned, and transported to the laboratory where the experiments were carried out. No sex identification was performed for these organisms.
Experimental exposure of the oysters
The oysters were divided into 16 20-L aquaria, containing filtered seawater
Results
Oyster mortality was observed only in the group exposed to the highest diesel oil concentration (1 ml L−1). Four oysters kept at salinity 35 ppt died during the oil exposure, two died during the 24-h depuration period, and three died during the 7-day depuration period. At salinity 15 ppt, one oyster died during the exposure period. No mortality was observed in the oysters exposed to diesel oil and further depurated in salinities 9 and 25 ppt.
Fig. 1 shows the GST activity in the digestive gland of
Discussion
The influence of salinity in biomarker responses is especially relevant in euryhaline mollusks, such as C. rhizophorae, which has been proposed as sentinel organism in biomonitoring programs in mangrove and estuarine zones (Nascimento et al., 1998; Wallner-Kersanach et al., 2000; Monserrat et al., 2002; Rebelo et al., 2003). Frequently these areas receive contaminant inputs associated to domestic and industrial effluent discharges and elevated stormwater runoff. In addition, these factors under
Acknowledgments
This work was supported by grants from Brazilian Agency CNPq-CTPetro No. 474513/01-7 and Plano Sul de Pesquisa e Pós-Graduação No. 520741/99-4. A.B. is a research fellow from CNPq. The authors thank Dr. Paulo S.M. Carvalho for revising the manuscript and the two anonymous referees for the excellent suggestions to improve the quality of the manuscript.
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2021, AquacultureCitation Excerpt :Our results are in agreement with such findings since the CAT activity of four strains decreased at the lowest salinity (15 and 20 psu) and increased significantly at 25 psu. In contrast, the bivalve C. rhizophorae increased biotransformation (GSTs) activity under low salinities (9–15 psu) and control pH, while CAT activity was maintained under different salinities (9, 15, 25 and 35 psu) (da Silva et al., 2005). Similarly, the CAT and glutathione S-transferase activities in C. gigas gills did not change when exposed to salinity fluctuations of between 9 and 35 psu (Zanette et al., 2011).