DNA Damage And Oxidative Stress Induced By Chlorpyrifos And TCP Exposure In Zebra-fish (Danio Rerio)

Chlorpyrifos is a broad-spectrum organophosphorus insecticide (O,O-diethyl -O-3,5,6-triehloro-2-pyridyl phosphorothioate) which is used in numerous agricultural and urban pest control. The primary metabolites of chlorpyrifos is 3,5,6-trichloro pyridine-2-phenol (TCP). Due to its strong water-solubility and mobility, this harmful metabolite exists in the environment in a certain amount. And the residue of TCP in the soil and water results the large environment pollution and the harm to living things. Although TCP has potentially harmful effect to organisms of environment, few researches were conducted to study that. Therefore, the aim of this study was to get more comprehensive understanding on the effects of chlorpyrifos and its metabolites TCP, and information about the potential ecological risk of this pesticide on the aquatic ecosystem.This study was operated to investigate the effect of Chlorpyrifos and TCP on the liver microsomal cytochrome P450 content, NADPH-P450 reductase, antioxidant enzymes [catalase (CAT) and superoxide dismutase (SOD)], ROS (Reactive Oxygen Species) generation and DNA damage in zebrafish. Male and female zebrafish were separated and exposed to a control solution and three concentrations of Chlorpyrifos (0.01, 0.1, 1mg L-1) and TCP (0.01, 0.1, 0.5mg L-1), sampled after 5, 10, 15, 20 and 25 days. The main results are showed as follows:1. SCGE (single-cell gel electrophoresis): In the SCGE test, the results showed that, Olive tail moments of Danio rerio was enhanced after treatment with different doses of Chlorpyrifos and TCP on the days 5, 10, 15, 20, and 25, and DNA fragmentation showed a dose-response relationship, DNA damage increased with increasing Chlorpyrifos and TCP concentrations, and significant differences were found compared to the controls.2. Cytochrome P450 enzymes: Chlorpyrifos and TCP significantly stimulates cytochrome P450 enzymes in zebrafish at concentrations of our experiment, even at the concentration of 0.01 mg L-1 could detect the response obviously. Moreover, gender-based differences were also observed.3. Antioxidant enzyme activity: Within the range of test Chlorpyrifos and TCP concentrations, antioxidant enzyme activity (CAT and SOD) could be induced by Chlorpyrifos and TCP. They increased at the low concentrations (0.01 and 0.1 mg/L) but decreased significantly after exposure to high concentrations (0.5 and 10 mg/L).4. ROS: Chlorpyrifos and TCP induced a significant increase of ROS generation in the zebrafish hepatopancreas. It should be noted that this research also discovered the interaction relationship among the four indictors induced by Chlorpyrifos and TCP. There was a very close relationship existed among the four indictors, which may be helpful to the future study of the mechanistic reactions of aquatic organisms to pollutant.In conclusion, comparing with chlorpyrifos, the impact of TCP was more intense in zebrafish, and its toxicity was greater. The potential ecological risk of chlorpyrifos and its metabolites TCP requires sufficient attention and further study.