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The effect of chlorine exposures on the survival of freshwater aquatic life is of major concern within many of the waterbodies in the United States. Continuous chlorine exposures are a typical result of effluent releases from wastewater treatment plants. Intermittent chlorine exposures are representative of the “blow down” antifouling procedure used for cooling towers in power plants.
The purpose of this paper is to present the derivation and resulting mathematical expressions for the time-concentration relationship of chlorine exposure and survival of freshwater aquatic organisms. Two topics will be discussed: the time-concentration toxicity relationship for constant chlorine exposures and the prediction from the constant exposure mathematical expressions of toxicity caused by intermittent exposures.
An extensive literature review provided the database from which mathematical time-concentration relationships were derived for constant chlorine exposures. Relationships were analyzed for individual species. The resistance of all the different species increased significantly from a 96-h exposure period to an 8-h exposure period.
The intermittent chlorine exposure tests differ not only in the frequency and duration of the chlorine dose but also in the geometric form of the dose application. A kinetic model, which accounted for these variabilities, was used to predict intermittent exposure mortality. The parameters of the model were obtained from the analysis of constant exposure results. In addition to predicting mortality resulting from variable exposure patterns, the kinetic model may be used to design appropriate test durations for intermittent chlorination experiments.
toxicity, chlorine, aquatic biology, chlorine exposure toxicity, kinetic toxicity model, time-concentration relationship, intermittent exposure, appropriate test duration
Technical staff, The MITRE Corporation, McLean, VA
Water resource engineer, Cosulting Engineers, Inc., Rescon, VA