Chronic effects of metals on their accumulation, DNA damage and oxidative stress in the fish

Abstract

The project “Chronic effects of metals on their accumulation, DNA damage and oxidative stress in the fish” was conducted in four phases i.e. (i) acute toxicity of metals to the fish (ii) chronic exposure based accumulation of metals in the fish (iii) DNA damage caused by chronic exposure of metals (iv) effects of chronic exposure of metals on oxidative stress in the fish. The acute toxicities (96-h LC50 and lethal concentration) of cadmium, chromium, copper, lead and metals mixture (Cd+Cr+Cu+Pb) were determined for 120 days old three species of fish viz. Catla catla, Labeo rohita and Cirrhina mrigala, separately (n=10), under controlled laboratory conditions. After determination of 96-h LC50 of selected metals and MM, all the three species of fish were exposed to 2/3rd, 1/3rd, 1/4th and 1/5th of their respective 96-h LC50 for 14, 28, 42, 56, 70 and 84 days, separately, and after each period of exposure the accumulation of metals in their organs and the extent of DNA damage in the peripheral erythrocytes and oxidative stress in terms of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities in the fish tissues were determined. The sensitivity of three species of fish, determined in terms of 96-h LC50, for all the individual metals and MM varied significantly, showing species-specific sensitivity towards each metals/MM. C. mrigala were significantly (p<0.05) less sensitive to all the individual metals and MM according to 96-h LC50. Exposure of metals mixture caused significantly higher toxicity to all the three species of fish, followed by Pb, Cu, Cd and Cr exposures. The accumulation of all metals in the fish exhibited significantly positive correlation with both dose and duration of exposure. Chronic exposure of metals caused their significantly higher accumulation in C. mrigala, followed by L. rohita and C. catla. However, the overall amassing of metals in the fish, during exposure of individual metal and MM followed the order: Cr > Cd > Cu > Pb. Fish gills, liver, kidney, muscle and brain exhibited significant variability for the accumulation of all the individual metals and MM. Fish liver and gills showed significantly higher ability to concentrate all metals while fish muscles showed significantly lowest ability to amass metals. The overall accumulation of metals in the organs of three species of fish followed the order: liver > gills > kidney > brain > muscles. The accumulation of all metals in the fish body showed significantly direct correlation with the concentration and duration of exposure. The chronic exposure of Cd, Cr, Cu, Pb and MM caused significantly variable damage to the DNA of peripheral blood erythrocytes of all the three fish species under investigation. However, C. mrigala exhibited significantly higher frequency of damaged nuclei, followed by L. rohita and C. catla. The genetic damage index (GDI) values for three species of fish, exposed to metals, varied significantly also. However, both C. mrigala and L. rohita showed significantly higher GDI values. The fish exposed to MM showed significantly higher mean GDI value while it was significantly lower due to Cd exposure. The overall nuclear damage in the fish, caused by individual metals and MM exposures, followed the order: MM > Cu > Pb > Cr > Cd. C. mrigala developed significantly longer tail length of comets while it was significantly lower in C. catla. There existed significant differences among individual metals and MM to induce comet tail lengths in the nuclei of fish erythrocytes. However, exposure of MM induced significantly longer tails, followed by Cu, Pb, Cr and Cd exposures. Therefore, both GDI and CTL of comets may be used to predict genotoxic potentials of various toxicants for the fish.