Antioxidant and malondialdehyde levels in the tissues of Heterobranchus longifilis following lethal and sublethal exposure to zinc oxide nanoparticles

Abstract

Increased industrial and domestic usage of zinc oxide nanoparticles (ZnO-NPs) informed their great demand, though scanty information exists on their environmental fate. Therefore, the impacts of ZnO-NPs on the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and malondialdehyde (MDA) levels in the blood, gill and liver of Heterobranchus longifilis (Mean length ± SD, 10.28 ± 1.34) exposed to lethal concentrations (0.00, 60.00, 80.00, 100.00 and 120.00 mg/l) and sublethal concentrations (0.00, 6.00, 8.00, 10.00 and 12.00 mg/l) of ZnO-NPs were examined for 96-h and 45 days, respectively. The results showed that during lethal exposure, SOD and GPx activities in the tissues of ZnO-NPs-exposed fish changed insignificantly (p > 0.05) compared to the control, except in liver where GPx changed significantly (p < 0.05). MDA levels in the blood and liver significantly increased, while no such change was observed in the gill. During sublethal exposure, SOD activities significantly increased at 10 and 12 mg/l after 15 days exposure, while after 30 days there was no significant change. However, after 45 days of exposure, significantly higher activities were recorded at the groups treated with 10 and 12 mg/l. GPx activity in the blood did not show a significant increase after 15 days exposure, but after 30 and 45 days the activity increased significantly than the control. Compared with the control, GPx activity in the gill neither show significant concentration- nor time-dependent difference between the first period of 15 days and the subsequent 15 days (i.e., 30 days) of exposure, until after 45 days at 12 mg/l of ZnO-NPs. In the liver, GPx activity increased significantly as ZnO-NPs concentration and exposure period increased compared with the control. In all the tissues, significantly higher MDA levels than the control was not observed until after 45 days exposure at 12 mg/l of ZnO-NPs. These results suggest that ZnO-NPs concentrations greater than those used in this study may produce deleterious effects on the antioxidant system during short- or long-term exposure and may thus, weakens the adaptive threshold of the fish.