Bioscience Methods 2024, Vol.15, No.4, 173-183 http://bioscipublisher.com/index.php/bm 174 Bioaccumulation of heavy metals in different tissues and at different levels in aquatic animals have been reported by several researches (Yu et al., 2021; Salami et al., 2023). This accumulation is never without a consequence at organismal and suborganismal levels of the exposed level. Ni et al., (2020) reported an acute toxic effect of hexavalent chromium on the liver of marine medaka (Oryzias melastigma). The presence of toxic heavy metals above tolerable limits in aquatic habitats has been reported to cause significant redox imbalance in the resident organisms (Galli et al., 2005; Pujalté et al., 2011; Raeeszadeh et al., 2023). Oxidative stress, which is a condition characterized by an imbalance between the production of reactive oxygen species (ROS) and the ability of cells to scavenge the excess ROS results in damage to biomolecular structures like lipids, proteins, and DNA (Adeyemi et al., 2013; Adeyemi, 2014; Xu et al., 2018; Chen et al., 2020). However, there is a scarcity of information on the effects of hexavalent chromium on the redox homeostasis of periwinkles at sublethal concentrations, which is considered to be important for the ecological risk assessment of hexavalent chromium in aquatic environments. This study hypothesizes that exposure to sublethal concentrations of Cr6+ disrupts redox homeostasis in T. fuscatus. Therefore, the present study investigated the effects of exposure to hexavalent chromium on the activities of antioxidant enzymes and the levels of lipid peroxidation and reduced glutathione, which are important biomarkers of oxidative stress in aquatic animals. 2Results The activity of superoxide dismutase (SOD) in periwinkles exposed to sublethal concentrations of hexavalent chromium is revealed in Figure 1. The activity of superoxide dismutase was significantly higher, in a concentration-dependent manner in periwinkles that were exposed to Cr6+ compared to the control (F3, 28 = 39.93; p ˂ 0.0001). The SOD activity was significantly lower in the animals exposed to 0.42 mg/L Cr6+ compared to those exposed to 0.84 and 4.2 mg/L Cr6+ in which the SOD activity was statistically similar. The control experiment produced the least activity of SOD, signifying that the control animals were the least stressed when compared to the other animals exposed to different concentrations of Cr6+. Figure 1 Superoxide dismutase activity in the soft tissue of T. fuscatus exposed to various sublethal concentrations of hexavalent chromium. Each bar represents the mean ± standard deviation of three replicates (n=8). Bars with different letters are significantly different There was a significant difference in the catalase activity among the groups (F3, 28=74.72; p ˂ 0.0001). Catalase activity was significantly higher in periwinkles that were exposed to hexavalent chromium compared to the control (Figure 2). The catalase activity was lowest in the animals that were exposed to 0.42 mg/L while there was no significant difference in the catalase activity between those exposed to 0.84 and 4.2 mgl/L Cr6+ (Figure 2). The activity of glutathione peroxidase (GPx) differed significantly among the groups (F3,28 = 6.55; p = 0.015). The GPx activity was significantly higher in the animals that were exposed to higher concentrations of Cr6+ (0.84 and 4.2 mg/L) compared to the control and those exposed to 0.42 mg/L Cr6+ in which the GPx activity was statistically similar. Also, the GPx activity was statistically similar between the 0.84 and 4.2 mg/L exposure groups (Figure 3).
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