The Joint Toxicity Of Cu²⁺, Cd²⁺ And TBT On Two Species Of Copepods

The paper studies the effect of three common pollutants copper(Cu²⁺), cadmium (Cd²⁺) and tributyltin (TBT) on two planktonic copepods, Schmackeria poplesia and Calanus sinicus , which widely distribute in coastal waters. In order to find the methods for studying the toxicity of pollutants and their joint toxicity on copepods, the activity of total superoxide dismutase(T-SOD) of copepod is chosen as the sensitive indicator in sublethal toxicity condition. The test will also provide data for studies of antioxidant defense reaction on copepods with exposure of pollutants and the joint toxicity of heavy metal ions and organic on copepods. The tests are separated into 4 parts as follows.In the first part, it studies the acute toxicity of copper, cadmium and TBT on S. poplesia and the joint toxicity of each pair of the three pollutions under the similar toxicity concentrations. Further more the joint toxicity of pollutants is studied with the Additive Index (AI) Method. In acute toxicity tests, the 96 hours lethal concentration of 50%: the 96h-LC50 of Cu²⁺on S. poplesia is 133.52μg/L, the 96h-LC50 is 442.68μg/L for Cd²⁺, and the 96h-LC50 is 0.4028μg/L for TBT. These results show that the acute toxicity of the three pollutants on S. poplesia is obtained from strong to weak with the order of TBT>> Cu²⁺> Cd²⁺. In joint toxicity tests the 96 hours lethal concentration of 50% of three pairs of pollutants copper and cadmium, copper and TBT, cadmium and TBT, are also tested. The result of joint toxicity on S. poplesia with the pollutants of copper and cadmium is S = 1.19, AI =- 0.19, with the pollutants of copper and TBT S = 2.23, AI =- 1.23, with the pollutants of cadmium and TBT S = 1.18, AI =- 0.18. For each of the three groups, the joint toxicity is antagonistic.In the second part, the activity of total superoxide dismutase (T-SOD) is measured as an indicator of the effect of toxicity on S. poplesia under the sublethal concentrations of copper, cadmium, and TBT. And the antioxidant defense system of S. poplesia is preliminarily studied when being exposed under the joint toxicity of pollutants. The results show that the T-SOD activity of the S. poplesia under the sublethal concentrations is sensitive to each group of pollutants in this test. The T-SOD activity shows significant induction or inhibition with the increase of exposing time. With single toxicity exposure, the variation trend of S. poplesia T-SOD activity is generally first increased and then decreased. the T-SOD activity reached maximum at 48h, 24h when the copepods were exposed in Cu²⁺, and Cd²⁺. There is no increase of its activity for TBT exposed. Except for the groups of low concentration Cu²⁺ and Cd²⁺, the T-SOD activities of all groups are inhibited in the end. The trend of T-SOD activity variation of joint toxicity is more complex, it's first decreased, then increased and at last decreased again. The T-SOD activities of all joint toxic groups are inhibited mainly. When the copepods are exposed in Cu²⁺-Cd²⁺, Cu²⁺-TBT, and Cd²⁺-TBT, the T-SOD activities reach minimum at 12²4h, 24h, and 36h.The rising trend later relates with the induction on metallothionein (MT) by metal ions or some other factors.In the third part, the joint toxicity under the concentrations of similar toxic of each pair of the three pollutants copper, cadmium and TBT on C. sinicus is studied through the Additive Index (AI) Method. The lethal concentrations of 50% for 96 hours of the three groups of pollutants are obtained: the joint toxicity for copper and cadmium S = 2.91, AI =- 1.91, for copper and TBT S = 2.58, AI =- 1.58, and for cadmium and TBT S = 17.13, AI =- 16.13. Joint toxicity of the three groups is more antagonistic than that of S. poplesia, especially the group of cadmium and TBT which shows the most obvious antagonist effect.In the last part, the activity of total superoxide dismutase (T-SOD) activity on C. sinicus is studied under the sublethal concentrations of copper, TBT and three pairs mixtures of the pollutants copper, cadmium and TBT. The trends of T-SOD activity variation of single pollutant copper, and TBT groups, and the joint pollutants group of cadmium with TBT show the similar characteristic. It's icreased at first, then decreased and increased again later, and is inducted obviously. Cadmium and TBT joint groups consistently show a higher antioxidant levels, and it's believed to correlate with the induction of MT and competing for binding site or some other factors. The trends of T-SOD activity variation of the groups of copper and cadmium and the groups of copper and TBT are correspondingly complicated, and the trends are increased first and then decreased all through. The joint toxicity of copper and cadmium shows the greatest toxicity with time continuing, and the T-SOD activity reaches minimum at 96h and appears inhibition trend. Compared with others, the joint toxicity of copper and TBT significantly increased with concentration.