Comparison of selected metals and pesticides for their acute toxicity and mutagenic effects on fish

Abstract

The comparison of selected metals and pesticides for their acute toxicity and mutagenic effects on fish was conducted in two phases (i) acute toxicity tests with fish (ii) chronic exposure based genotoxic effects on the fish. Acute toxicity tests were conducted with 180 days old three fish species viz. Cyprinus carpio, Oreochromis niloticus and Ctenopharyngodon idella to determine their 96-hr LC50 and lethal concentrations for water-borne Pb+Cd, Pb+Co, Cd+Co, Pb+Cd+Co, chlorpyrifos+endosulfan, chlorpyrifos+bifenthrin, endosulfan+bifenthrin and chlorpyrifos+endosulfan+bifenthrin mixtures, separately, under controlled laboratory conditions. Bio-accumulation of metals/pesticides in the fish body at acute (96-hr LC50 and lethal concentrations) and chronic sub-lethal exposures were also determined. After finding the 96-hr LC50 values of each mixture for the three species, the three groups of each fish species viz. Cyprinus carpio, Oreochromis niloticus and Ctenopharyngodon idella were exposed to 1/3rd, 1/4th, 1/5th and 1/6th of their respective LC50 values of each treatment (metals/pesticides mixture), separately, for 84-days in the glass aquaria. The chronic effects treatments were examined on (i) accumulation of metals/pesticides in the fish body and (ii) mutagenic effects of metals/pesticide mixtures on the three fish species. Fish body organs viz. kidney, liver, gills, skin and muscles were analyzed for their respective exposure metals while for the determination of pesticides, whole fish body oil was used. Fish blood samples were taken from the caudal veins after 14, 28, 42, 56, 70 and 84 days of metals /pesticide mixture exposures, separately, and fish peripheral erythrocytes were analyzed by using comet bioassay. The mutagenic effects of metals/pesticides mixtures on the three fish species were determined in terms of DNA damage measured as damaged nuclei (%), GDI and cumulative tail length of comets (μm). Acute toxicity (96-hr LC50 and lethal concentrations) of metals mixtures viz. Pb+Cd, Pb+Co, Cd+Co and Pb+Cd+Co and pesticides mixtures i.e. chlorpyrifos+endosulfan, chlorpyrifos+bifenthrin, endosulfan+bifenthrin and chlorpyrifos+endosulfan+bifenthrin to the three fish species viz. Cyprinus carpio, Oreochromis niloticus and Ctenopharyngodon idella varied significantly at p<0.05. Among the metals mixtures, Pb+Cd+Co caused significantly higher mean toxicity to all the three fish species, followed by Cd+Co mixture while Pb+Co exhibited significantly least toxicity to the fish in terms of 96-hr LC50 and lethal concentrations. However, the tertiary mixture of pesticides i.e. chlorpyrifos+endosulfan+bifenthrin was significantly more toxic to all the three species, followed by that of binary mixtures i.e. chlorpyrifos+endosulfan, endosulfan+bifenthrin and chlorpyrifos+bifenthrin. Cyprinus carpio were significantly more sensitive to all the metals/pesticides mixtures, followed by that of Ctenopharyngodon idella and Oreochromis niloticus. Exposure of mixtures at both 96-hr LC50 and lethal concentrations caused significantly variable uptake and accumulation of metals and pesticides in three fish species. The exposure of Pb+Cd+Co mixture caused significantly higher accumulation of these metals in all the three fish species while Cd+Co mixture showed significantly least accumulation tendency. All the three fish species showed significant differences in their ability to accumulate metals in their body organs. In general, the uptake and bio-accumulation of metals in the three fish species followed the order: kidney > liver > gills > skin > muscles. Among pesticide mixtures, the exposure of chlorpyrifos+bifenthrin mixture to the fish caused significantly higher amassing of both these pesticides, followed by that of endosulfan+bifenthrin, chlorpyrifos+endosulfan and chlorpyrifos+endosulfan+bifenthrin. The overall tendencies of three fish species, to accumulate metals and pesticides in their bodies, followed the order: Oreochromis niloticus > Ctenopharyngodon idella > Cyprinus carpio. Fish species showed significant differences in their ability to accumulate metals and pesticides during chronic exposure of various concentrations viz. 1/3rd, 1/4th, 1/5th and 1/6th of LC50 for 84 days. Oreochromis niloticus showed significantly higher ability to bio-concentrate metals and pesticides as compared to Ctenopharyngodon idella and Cyprinus carpio. The chronic exposure of Pb+Cd+Co mixture caused significantly higher accumulation in the fish while Cd+Co mixture showed significantly lower tendency to cause amassing of both these metals in the fish body. Both time and concentration based amassing of metals in the body organs of all the three fish species followed the order: kidney > liver > gills > skin > muscles. Exposure of chlorpyrifos+bifenthrin mixture caused significantly higher amassing in the fish body, followed by that of chlorpyrifos+endosulfan+bifenthrin, chlorpyrifos+endosulfan and endosulfan+bifenthrin mixtures. The accumulation of metals/pesticides increased concomitantly with the exposure duration and concentration of the mixture in the media. Both the duration and concentration based amassing of pesticides in the bodies of three fish species followed the order: Oreochromis niloticus > Ctenopharyngodon idella > Cyprinus carpio. The extent of DNA damage, determined in terms of damaged nuclei (%), GDI and cumulative tail length of comets (μm), varied significantly (p<0.05) due to exposure of various concentrations of metals/pesticide mixtures, negative and positive control treatments. The toxic potential of metals/pesticides to induce DNA damage in the peripheral blood erythrocytes of three fish species, determined in terms of damaged nuclei (%), followed the order: chlorpyrifos+endosulfan+bifenthrin > chlorpyrifos+endosulfan > endosulfan+bifenthrin > chlorpyrifos+bifenthrin > Pb+Cd+Co > Cd+Co > Pb+Cd > Pb+Co. Genotoxic damage in terms of GDI and cumulative tail length of comets were significantly higher due to exposure of chlorpyrifos+endosulfan+bifenthrin mixture while Pb+Co mixture caused significantly least damage to the fish DNA. Regarding toxicity indices of three fish species, Cyprinus carpio appeared significantly more sensitive to all the mixtures as their erythrocytes showed significantly higher percentage of damaged nuclei (39.20±11.45%), followed by that of Ctenopharyngodon idella (35.24±10.48%) and Oreochromis niloticus (30.47±10.74%). The 1/3rd LC50 exposure of metals/pesticides mixtures to all the three fish species caused significantly higher DNA damage while negative control had significantly least damage for the nuclei. The frequency of damaged nuclei, GDI and cumulative tail length of comets increased concomitantly with the duration of exposure i.e. from day 14th to day 56th while it showed decreasing trend afterwards. The time dependent decrease in DNA damage after 56th day of exposure would be due to repairing of damaged DNA or loss of heavily damaged cells or both. This shows interspecies variability in DNA damage due to significant differences in their uptake, accumulation, metabolism, excretion and fish ability/efficiency to repair damaged DNA. The exposure of pesticide mixtures caused significantly more damage to the DNA of all the three fish species than that of metals mixtures. Furthermore, all the three fish species were significantly more sensitive to pesticides as reflected in their DNA damage occurring at very low concentration of all the mixtures. Moreover, comet bioassay appeared as a rapid and sensitive method for quantifying and analyzing the DNA damage in the peripheral erythrocytes of three fish species viz. Cyprinus carpio, Oreochromis niloticus and Ctenopharyngodon idella that can be used as bio-indicator of aquatic pollution in the natural habitats.