Abstract: To evaluate impact of printing-dyeing wastewater on aquatic ecological systems,an experiment was carried out using Scenedesmus obliquus, Daphnia magna and Hemibarbus maculates as subjects for test of toxicity of printing-dyeing wastewater.In the experiment the wastewater was diluted with 7346-2 standard diluent into solutions different in concentration,i.e 100.00%,50.00%,25.00%,12.5%,and 6.25%.Results show that the wastewater was somewhat toxic to all the three kinds of aquatic organisms in the aquatic ecosystem regardless of its nutrient level.The 24 and 48 h-EC₅₀(effective concentration for reduction of growth by 50%)of the wastewater was (51.55±4.12)% and (20.40±6.27)%,respectively,to S.obliquus,and (78.20±4.31)% and (53.10±1.88)%,respectively,to D.magna.The 96h-LC₅₀ of the wastewater to cleavage stage,blastula stage,gastrula stage,lava,and 25-day fingerlings of H.maculates was (19.89±1.68)%,(25.95±2.14)%,(27.24±0.88)%,(19.61±2.21)%,and (49.27±3.27)%,respectively.The safe concentration of the wastewater to aquatic organisms was 1.96%.So,discharge of such wastewater should be strictly controlled in practice.

Key words: printing-dyeing wastewater, Scenedesmus obliquus, Daphnia magna, Hemibarbus maculates, toxicity