Abstract
A Ceriodaphnia dubia reproductive inhibition test method was proposed for whole effluent toxicity (WET) management by the National Institute for Environment Studies. However, in this method, the complex influence of residual chlorine in wastewater and countermeasures are not described. In this study, the popular, convenient and economical Daphnia magna acute toxicity test, which was recommended by Nishida et al. and authors, was conducted for wastewater before and after chlorine disinfection at six factories, as well as wastewater from which residual chlorine was eliminated by adding sodium thiosulfate after chlorine disinfection, and for aqueous solutions of hypochlorite. As a result, it was verified that toxicity was exhibited to Daphnia with the residual chlorine of 0.15 mg L-1 or more in wastewater, but 0.01 - 0.02 mg L-1 or more in hypochlorite solutions. The toxicity of the wastewater after the elimination of the residual chlorine was less than that of the wastewater after chlorine disinfection. It is appropriate, for WET management, that the toxicity test be conducted on wastewater after the elimination of residual chlorine by adding an adequate amount of sodium thiosulfate.
