Evaluation on Joint Acute Toxicity of Bata-Cypermethrin and Chlorpyrifos to Freshwater Protozoan Community

The joint acute toxicity of chlorpyrifos and bata-cypermethrin on freshwater protozoan community was examined with the polyurethane foam unit method. Forty-eight-hour LC50 values were 8.72 mg/L for chlorpyrifos and 1.92mg/L for bata-cypermethrin in individual acute toxicity test. Our data indicated that the extent of toxic interactions of two insecticides showed synergism in 48h exposure. Additive Index (AI) was 2.2 associated to the joint acute toxicity test. In addition, the structure of protozoan community was simplified and the functional-trophic groups changed with the increasing concentration of insecticides. The species and population of Algivores(A) and Predators Raptors (P) reduced but Bactivoresdetrivores(B) became predominant relatively.