中文摘要：

以草鱼（Ctenopharyngodon idellus）为实验材料，研究并比较了重金属镉（Cd）与锌（Zn）对草鱼的单一与联合毒性．在此基础上，根据水生毒理联合效应指数相加法原理，利用生物测定计数型机值分析得到毒性单位浓度LC50值进行判断．结果表明，Cd对草鱼的毒性大于Zn．Cd、Zn对草鱼96h的半致死浓度分别为26．87和33．14mg·L^-1；Cd与Zn对草鱼的联合毒性在48h为拮抗作用，在96h表现为协同作用．以草鱼肝脏组织超氧化物歧化酶（SOD）活性影响为指标，Cd与Zn的联合作用与Cd、Zn的暴露剂量和暴露时间都有密切关系：草鱼肝脏SOD活性应激反应对低浓度Zn（0．4TU）暴露较敏感，对高浓度Cd（0．8TU）的暴露较敏感，SOD活性能迅速产生应激性升高；48h时Cd与Zn的联合毒性显示为拮抗作用，96h时Cd与Zn的联合毒性显示为协同作用．

英文摘要：

The single and joint toxicity of Cd and Zn to grass carp （ Ctenopharyngodon idellus） and the Superoxide Dismutase （SOD） activity in carp liver were examined. The evaluation of the joint toxicity of Cd and Zn was carried out based on the principle of the additive index of aquatic toxicological effects, and LC50 was obtained with the SPSS 11.5 software package by probit analysis of the bioassay. The results showed that the toxicity of Cd was greater than that of Zn. The 96 h LC50 of Cd was 26.87 mg. L^-1 and of Zn was 33.14 mg·L^-1. The joint toxicity turned out to be related to the exposure time, showing antagonism by 48 h and synergism by 96 h. The SOD test results showed that the joint toxicity was both related to the exposure time and the exposure dose, which validated the results of the toxicity tests. Also the SOD test results showed that in the case of the low toxicity concentration （0.4TU）, the liver SOD activity responded more quickly to Zn than to Cd. In the case of high toxicity concentration （0.8TU） the opposite was true and the SOD activity was more sensitive to Cd than to Zn.