Metals’ Molecular Toxicity In Tadpole (Bufo Gargarizans)Exposed To Copper, Cadmium And Combined Pollution

To investigate the molecular-toxicity mechanism of Copper (Cu2+), Cadmium (Cd2+) and their combined pollution to the amphibian, we used the standard determination technique of aquatic biological toxicity from Bufo gargarizans tadpoles following whole-body exposure to different concentrations of the tested substances. The study was conducted to examined the Na+-K+-ATPase activities, antioxidant enzymes (SOD, CAT, GSH-Px) activities, the change of LPO and EST isozyme and the damage of DNA. The results of this research were as below:1. The effects of Cu2+、Cd2+single and combined pollution on the Na+-K+-ATPase activities in tadpoles were observed. The results showed that the Na+-K+-ATPase activities of tadpoles elevated at the low concentration of Cu2+and Cd2+, while they increased significantly at the group of0.0298mg/LCu2+and1.14mg/L Cd2+compared to the control group. But with Cu2+and Cd2+concentration increased, the damage of tadpoles were much heavier, the Na+-K+-ATPase activity was gradually decreased and was even inhibited significantly. The joint effects of the combined pollution on the Na+-K+-ATPase activity were synergistic.2. The studies of Cu2+, Cd2+and their combined pollution on antioxidant enzyme activities in Bufo gargarizans tadpole indicated that SOD, CAT and GSH-Px activities were increased significantly at0.0298mg/L Cu2+group. But the SOD, CAT and GSH-Px activities were fall to control or decreased significantly with the Cu2+concentration increased. In the tadpoles exposed to the dosage of Cd2+, the SOD, CAT and GSH-Px activities were first declined and then raised to control levels with Ca2+concentration increased. joint toxic effects of these two heavy metals on the SOD、CAT、GSH-Px activities were synergistic. The above results indicated that the increasing of antioxidase enzyme activities (SOD, CAT and GSH-Px) would be part of general defense strategies to cope with oxidative stress.3. The effects of Cu2+、Cd2+single and combined pollution on the LPO of tadpole were observed. The results showed that the MDA contents were increased significantly at the group of0.0298mg/LCu2+but GSH contents were not obvious. MDA and GSH contents were decreased significantly with Cu2+concentration increased. At the group of1.710mg/LCd2+, the MDA and GSH contents of tadpoles increased significantly. The joint effects of the combined pollution to them were synergistic. It was obvious that LPO can be induced by Cu2+, Cd2+and their combined pollution, and the LPO followed the order:metal mixture>Cu2+>Cd2+. However the damage was reduced while the higher GSH contents.4. The results showed that the changes of EST isozymes induced by Cu2+were mostly in the enzyme quantity (activity) and no new isozyme was found. The EST5change was the most sensitive to different Cu2+concentrations, so it could be used to indicate the Cu2+pollution stress. The changes of EST isozymes induced by Cd2+were both in the enzyme quantity (activity) and the numbers of isozyme band, and the absence of EST3was the special marker which could be used as a biomarker to indicate the Cd2+toxicity to organism. The joint effects of the combined pollution on EST isozyme were synergistic.5. The impacts of Cu2+, Cd2+and their combined pollution on DNA of Bufo gargarizans tadpoles indicated that DNA damage caused by Cu2+and Cd2+became more serious with their increasing concentration. Single-strand break was caused by Cu2+and Cd2+in low concentration, and high concentration led to double-strand break. Cd2+in certain concentration could increase the toxicity of Cu2+in complex pollution system.