Effect of chronic exposure to pesticide methomyl on antioxidant defense system in testis of tilapia (Oreochromis niloticus) and its recovery pattern

Abstract

The chronic effect of environmental methomyl on the antioxidant system in testis of Nile tilapia (Oreochromis niloticus) and its recovery pattern was investigated. Tilapia were exposed to sublethal concentrations of 0.2, 2, 20 and 200 µgL−1 methomyl for 30 days and thereafter moved to methomyl-free water for 18 days. Antioxidant levels in testis, including glutathione peroxidase, catalase, glutathione-S-transferase, glutathione reductase, superoxide dismutase, reduced glutathione, oxidized glutathione were measured every 6 days during the period of exposure, and at 18 days after being transferred to methomyl-free water. The results showed that lower methomyl concentration (0.2 µgL−1 ) had no effect on the above antioxidants, thus 0.2 µgL−1 could be seen as NOAEL for methomyl to tilapia. However, higher methomyl concentration of 2, 20 and 200 µgL−1 could significantly influence the above antioxidants. Glutathione peroxidase and oxidized glutathione increased significantly. On the contrary, reduced glutathione decreased significantly. Catalase, superoxide dismutase, glutathione reductase, glutathione-S-transferase increased at lower methomyl (2 and 20 µgL−1 ), but decreased at higher methomyl (200 µgL−1 ). The recovery test showed that oxidative damage caused by lower methomyl of 2 and 20 µgL−1 was reversible, and oxidative damage caused by higher methomyl of 200 µgL−1 was irreversible within 18 days of recovery period.