Living limits about Na
+ and Cl
-concentrations of larva of dragonfly were studied. As Na
+ and Cl
- concentrations in river water increased, the number of larva decreased and species composition of larva changed from Stylogomphus suzukii to Calopterx atrata. Na
+ and Cl
- concentrations were thought to be mixing ratio of domestic sewage and domestic sewage was thought to contain toxic substance. Davidius nanus was distributed widely in the river water from low to high mixing ratio of domestic sewage. Living limits of maximum Na
+ and Cl
-concentrations for Calopterx atrata and Davidius nanus were 50 and 80 mg/l. The values were living limit of all larva of dragonfly observed in the southern part of Osaka. In the long term, the living limits of maximum Na
+ and Cl
- concentrations for larva of dragonfly were 38 and 59 mg/l. When anionic surface active agent is 3.8 to 6.2mg/l, larva of dragonfly disappeared.
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