Bioscience Methods 2024, Vol.15, No.4, 173-183 http://bioscipublisher.com/index.php/bm 176 The levels of thiobarbituric acid reactive substances (TBARS) in the tissue homogenates of the periwinkles differed significantly (F3,24 = 32.18; p ˂ 0.0001). The TBARS levels were significantly lower in the periwinkles exposed to 0.84 and 4.2 mg/L Cr6+ compared to the control, while the TBARS levels were significantly higher in the animals exposed to 0.42 mg/L Cr6+ compared to the control and the other exposure groups (0.84 and 4.2 mg/L) (Figure 5). Figure 5 The levels of thiobarbituric acid reactive substances (TBARS) 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 3 Discussion Oxidative stress resulting from perturbation of redox homeostasis is a physiological disturbance that has been linked to exposure to toxic elements in several aquatic organisms (Lee et al., 2019; Nowicka, 2022; Saç and Yeltekin, 2023). The focus of the present study was oxidative stress effects in periwinkles due to exposure to sublethal concentrations of hexavalent chromium. The results obtained show a significant oxidative stress effect in the exposed periwinkles along concentration gradients, which are consistent with the findings of previous studies that have reported oxidative stress effects in aquatic organisms that were exposed to hexavalent chromium (Lushchak et al., 2009; Lushchak 2011; Aliu et al., 2023). Changes in the activity of antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase have been used as indices of oxidative stress in aquatic animals (Niki, 2008; Adeyemi, 2014; Aliu et al., 2023). The changes in the activity of antioxidant enzymes were due to the action of the enzymes to scavenge the reactive oxygen species produced in the cells in response to exposure to toxicants. Natural antioxidants level has also been reported to increase against reactive oxygen species produced by cadmium toxicity (Unsal et al., 2020; Huchzermeyer et al., 2022). Superoxide dismutase is an antioxidant enzyme involved in the conversion of toxic superoxide anions to hydrogen peroxide and molecular oxygen. Since hydrogen peroxide is equally toxic to cells, it is further acted upon by other enzymes such as catalase and glutathione peroxidase, which reduce it to water and molecular oxygen (Unsal et al., 2020; Huchzermeyer et al., 2022). The lack of significant difference in the activities of the antioxidant enzymes between the control and the animals exposed to 0.42 mg/L Cr6+ is an indication that the rate of production of ROS at this concentration was within the range that can be detoxified by the enzymes, thus preventing oxidative stress. On the other hand, the significantly higher activities of SOD, CAT, and GPx in the periwinkles exposed to 0.84 and 4.2 mg/L is an indication that the rate of production of ROS within these concentration ranges overwhelmed the scavenging activities of the antioxidant enzymes. This submission is similar to the submission of Schiebar and Chandel (2014) who reported that response to ROS is usually insignificant at low concentration of xenobiotic. Furthermore, hormesis can also set in, a rear condition in which lower concentration of stressor will produce more oxidative stress than higher concentration of same stressor. Aliu et al., (2023) also reported a significant increase in SOD activity in hexavalent chromium exposed catfish along exposure concentration gradient.
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