Residual Toxicity of Several Disinfectants in Domestic Wastewater

This study determined the residual toxicity associated with secondary effluents disinfected with chlorine, ozone, and bromine chloride, and with chlorinated effluent dechlorinated with sulfur dioxide. Each of these parallel disinfected effluent streams, as well as a nondisinfected effluent stream, was used in a life cycle toxicity study with the fathead minnow, Pimephales promelas. Mean total residual chlorine and bromine chloride concentrations as low as 0.033 and 0.034 mg/l, respectively, adversely affected fathead minnows. Dechlorination with sulfur dioxide eliminated the adverse effects of residual chlorine. No effects were observed on fathead minnows exposed to mean residual ozone concentrations of 0.016 mg/l or less.