DNA Damage and Histopathological Alterations in Muscles and Gill Tissues of Danio rerio (H.) Induced by Combined Exposures of Imidacloprid and Endosulfan

Abstract

Pesticide residues in environment pose significant harmful impacts on telTestrial and aquatic ecosystems. In the present study the combined exposure of imidacloprid and endosulfan on Zebrafish in telIDS of oxidative stress and DNA damage in liver and histological alterations in gills and muscles and impacts on antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), lipid peroxidation product malondialdehyde (MDA) were evaluated. Zebrafish were distributed in four different aquariums: control group without pesticide exposure (Fl), Treatment 1 (Tl), Treatment 2 (T2) and Treatment 3 (T3) and were exposed to constant imidacloprid concentration in all three treatments (lppm) and increasing concentrations of endosulfan from 0.5Jlg/L in Tl to O.IJlg/L in T2 and IJlg/L in T3. Fish sampling was done after 7, 14 and 21 days of exposure. Dose and time dependent decrease in superoxide dismutase (SOD) and catalase (CAT) activity was observed aftei· 21 days of exposure while the lower concentrations of pesticides induced SOD and CAT activities after early exposure to reduce the oxidative stress. Substantial increase of 98.6, 70.2 and 22.6% was observed in SOD activity in Tl, T2 and T3 as compared to control on day 7 while a significant decline of 55.1 % was observed in T3 after 21 days of exposure. Similarly, 47.4% increase in CAT activity was observed after 14 days of exposure. Malondialdehyde (MDA) levels increased significantly in the groups having the highest concentrations of pesticides at all sampling intervals. 36.8 and 66.2% increase in MDA content in T2 and T3 after 21 days of exposure was observed as compared to control. This study reveals the genotoxic potential of endosulfan and imidacloprid. DNA damage was measured through comet assay and increased DNA damage was observed in T3 after 21 days of exposure as compared to all treatments and control groups. Histopathological alterations in gills and muscles were dose and time dependent but the morphological changes in gills were more significant than muscles. Prolonged exposures induced epithelial lifting, pronounced hyperplasia, fused secondary lamellae, nalTowed water, shOltening of secondary lamellae and sloughing of lamellae in gills. Splitting of muscle bundles and sloughing of gills was randomly observed in groups having highest concentrations of pesticides (T3) after prolonged exposure of 21 days. The present study provides data regarding the combined exposure of imidacloprid and endosulfan to zebra fish.