Joint Effects And Toxicological Mechanisms Of Triazophos, Fipronil, Cd～(2+), And Pb～(2+) On Freshwater Fish Pseudorosbora Parva

Combined pollution has become one of the important directions of research in environment science at present. Before now most of the research has concentrated on the action of single compounds against organisms. When two or more chemicals are applied simultaneously to a living system or unit, the combined effect may be one of the followings: additive action, antagonism and synergism. Due to the presence of multiple pollutants including metals in natural environments, studies on joint-action toxicity are becoming increasingly popular. These studies are indispensable to measuring and predicting impacts of chemical pollutants on organism. However, studies of the joint toxicity of pesticides and metals in the aquatic ecosystem were few.Insecticide (e.g., fipronil and triazophos) and heavy metals (e.g., cadmium and lead) are two contaminants that are widely found in streams and wastewater effluents, and they are also toxic to most species in the water environment. These chemicals may have indirect or direct effect on enzymes. Acetylcholinesterase (AChE), hepatic glutathione-S-transferases (GST) and liver esterases are important biomarkers that can indicate the effect of xenobiotics on exposed organisms including fish.The study showed that toxicity of chemical toxicants was influenced by water quality. In tap water LC50 (96h) values of fipronil, triazophos, and Cd2+were measured to be 0.205mg/L, 0.004 mg/L, and 6.294mg/L, respectively, while in deionized water the LC50 (96h) values of fipronil, triazophos, Cd2+, and Pb2+ were measured to be 0.481 mg/L, 0.060 mg/L, 0.732mg/L, and 10.265mg/L, respectively. This meant that the topmouth gudgeon was more sensitive to fipronil and triazophos than to Cd2+ and Pb2+.The joint toxicity of triple and binary mixtures of pesticides and heavy metals against topmouth gudgeon (Pseudorosbora parva) are carried out in laboratory. The results showed that the mixtures of fipronil and triazophos (5.3 : 1, w/w), Pb2+ and Cd2+ (56 : 1), fipronil-triazophos and Cd2+ (5.3 : 1 : 202), fipronil-triazophos and Pb2+ (5.3 : 1 '. 175) are synergism under normal condition, while the mixtures of fipronil-triazophos and Pb2+ (5.3 : 1 : 1071) show additive action.Investigations were carried to assess the sublethal effects of the insecticides(fipronil and triazophos) and the heavy metals (Cd2+ and Pb2+) on activities of brain acetylcholinesterase(AChE), hepatic glutathione-S-transferases(GST) and liver esterases in Pseudorosbora parva. The results showed that within the range of the dosages of exposure, the activities of brain AChE and liver esterases were found to be inhibited by treatment I -III(fipronil-triazophos and Cd2+), treatment IV-VI(fipronil--triazophos and Pb2+), and triazophos, and the inhibitions of the enzyme increased with the concentration of these compounds, showing a statistically significant dose-response relationship, which can, therefore, be used as a practical biomarker for combined exposure of organophosphorous (OP) insecticides and metals. GST was found to be induced by both treatment I -III and treatment IV-VI at 48h. But in the low concentrations, the inhibitions of hepatic GST activities by treatment I -III and treatment IV-VI were detected with a range of 5.5-9.4 and 46.6-53.7% at 96h, respectively. The rate of inhibition of treatment IV-VI was higher than treatment I -III. It is suggested that the three biotransformation enzymes may be directly or indirectly affected by the tested chemicals.