Bioscience Methods 2024, Vol.15, No.4, 173-183 http://bioscipublisher.com/index.php/bm 177 Like the actions of antioxidant enzymes, reduced glutathione (GSH) played an important role in redox homeostasis of aquatic animals (Mello et al., 2015; Samuel et al., 2022). The thiol group of the GSH binds to ROS to form oxidized glutathione (GSSG), thus the cellular levels of GSH and the ratio of GSSG to GSH have been employed as biomarkers of oxidative stress in animals (Forman et al., 2009; RajRai et al., 2021). The significantly low levels of GSH in periwinkles exposed to higher concentrations of hexavalent chromium is an indication of oxidative stress in which GSH binds to ROS thus resulting in the depletion of cellular levels of GSH. This report is similar to the submission of Liu et al. (2022) who reported an imbalance in ROS/GSH in stressed organism and depletion in GSH level in an environment where ROS production is excessive One consequence of elevated production of reactive oxygen species in living cells is the oxidative damage to biomolecules e.g. peroxidation of lipid molecules (Dorts et al., 2009). Lipid peroxidation has been quantified in aquatic organisms by measuring the tissue levels of thiobarbituric acid reactive substances, which is a red- or pink-coloured final product of lipid peroxidation (Samuel et al., 2022; Osagie and Morayo, 2023). The significantly higher level of TBARS in periwinkles exposed to 0.42 mg/L Cr6+ is evidence of oxidative stress at the low exposure concentrattion. Notwitstanding, the activities of antioxidant enzymes did not support oxidative stress at the exposure concentration. However, the levels of TBARS were significantly low at higher exposure concentrations (0.84 and 4.2 mg/L) in this study. This could be as a result of increased activity of antioxidant enzymes at high exposure concentrations, which helped to scavenge the deleterious ROS, thus minimizing lipid peroxidation (Barata et al., 2005). 4 Conclusion The findings from the study indicate that the exposure to sublethal concentrations of hexavalent chromium resulted in oxidative stress in periwinkles as demonstrated by significant high activity of antioxidant enzymes and depletion of GSH level, especially at higher exposure concentrations (0.84 and 4.2 mg/L Cr6+). Although, the activity of the antioxidant enzymes did not suggest the incidence of oxidative stress in periwinkles exposed to a low concentration of Cr6+ (0.42 mg/L), however, the results of the lipid peroxidation revealed chromium-induced oxidative stress. This could be an indication that measuring the level of thiobarbituric acid reactive substances is a sensitive biomarker of oxidative stress at low exposure concentrations. The proper understanding of the oxidative stress patterns in aquatic animals like periwinkles can be used as biomarkers for early warning signals of environmental stress and potential ecological harm, even before visible effects like mortality or population decline play out. 5 Materials and Method 5.1 Collection of periwinkles The experimental periwinkles were got from marine water in Abealala, Ilaje Local Government, Ondo State, Nigeria (6o21′18″ N4o66′10″ E). The ambient salinity of the marine water at the collection point was found to be 7.9 ppt. The periwinkles collected where for this experiment were of table size of shell lengths between 4 and 5 cm and the mean body weight of 4.2 ± 0.8 g. After collecting water and sufficient periwinkles from the location, the samples were transported to the Postgraduate Research Laboratory of the Department of Biology, Federal University of Technology, Akure, Nigeria, in pristine plastic containers. Before the exposure of the periwinkles to hexavalent chromium, the organisms were given fourteen days to acclimate to the laboratory conditions and were fed water leaves (Talinum triangulare) during the period of laboratory acclimation. Using atomic absorption spectrophotometry, the total chromium concentration of the brackish water samples taken from the periwinkles collection point was found to be 0.3 mgl-1. 5.2 Periwinkle exposure to hexavalent chromium The laboratory-acclimatized periwinkles were exposed to three sublethal concentrations; 0.42, 0.84, and 4.2 mg/L being 1/ 20, 1/ 10, and 1/ 2 of the 96 h LC50 of Cr 6+, respectively for thirty (30) days. The LC50 (median lethal concentration) was previously determined in an earlier experiment (Salami et al., 2023). Throughout the experiment, the exposure medium was changed out every four days to avoid excretory product buildup in the experimental medium. Three replicates were established for each treatment, and the animals were exposed to Cr6+
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