Bioassay is necessary for assessment of pollution. Because physical and chemical taste are not enough for assessment of potential effects on water ecosystem. Bioassay tests have alot of scientific value inanition doing of them is easy and need less time, also need less space, laboratory equipment's and expenditure. Therefor such tests have found special attention in water pollution control measure. So whit determine of effluent toxicity and survey of its effects on water ecosystem by bioassay

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... thod, can determine the degree and the kind of treatment that are necessary to having optimum condition for water ecosystem. In this research survey of indicator toxicity of Isfahan south wastewater treatment by daphnia magna has been studied. Materials and methods: In this study experiments were done on samples of wastewater that has been taken from Isfahans south wastewater treatment (samples has been taken from four place, influent raw wastewater, before and after primary settling tank and after secondary settling tank). Primary daphnia were couch from there living sites, then one of them were cultured alone, after infants of primary daphnia were used for culture in large amount. After prepering necessary dilution of wastewater samples by doing necessary experiments LC50-48-h toxic unit, efficiency of different units and total of wastewater treatment plant were determined. Findings: Results reveal that LC50-48-h of influent wastewater is 30%(v/v) and toxic unit is 3.33 and LC50-48-h of wastewater before primary (after preliminary treatment) settling tank, after primary settling tank and after secondary settling tank was determined 32%, 85% and 32% (v/v) respectively, that was on the basis acute toxic unit (ATU) 3.125, 1.92, and 1.76 respectively, efficiency of preliminary treatment in reducing toxicity were determined 6% and efficiency of primary treatment secondary treatment and whole of treatment plant in reducing toxicity were determined 38.4%, 8% and 50% respectively . Conclusion: Data of this resear [...]