The Effects of Residual Chlorine on the Behavioural Responses of Daphnia magna in the Early Warning of Drinking Water Accidental Events

Biological Early Warning System (BEWS) based on behavioural responses of aquatic organisms was applied to monitor the drinking water quality for the early warning of accidental events. But residual chlorine in drinking water after disinfection might affect the behaviour modes of tested animals. In this research, the results showed that the residual chlorine in drinking water that was more than 0.32 mg/L would affect the behavioural responses of Daphnia magna significantly. It was evident dose-effect relationships between concentrations of residual chlorine and the behavioural responses of Daphnia magna. After 1.75 mg Na2S2O3 was added in 1 L water bodies, the behaviour modes of Daphnia magna would maintain the same as in Standard Reference Water (SRW). Therefore, in the early warning of drinking water accidental events, the effects of residual chlorine on the behavioural responses of Daphnia magna could be eliminated by on-line dosing of Na2S2O3.