Predictions of potential human health and ecological risks from power plant discharges of total residual chlorine and chloroform into rivers

Low levels of chlorine residual and the trihalomethane chloroform can be released from power plant discharges and enter natural surface water bodies. Such effluents may pose potential human health and ecological risks. To evaluate these risks, a model was developed and applied to a time-variable release of these constituents into a river. The release pattern and dose are typical of power plants. In situ formation of chloroform is also simulated. The model is applicable to situations where chloroform is the dominant trihalomethane. Therefore, the model is limited to water with low background bromide ion concentrations (approximately 50 mu g/L or less). For the scenario evaluated, predicted total residual chlorine levels, expressed in terms of a hazard quotient for the protection of aquatic organisms, are above EPA criteria at locations to within approximately 5 km downstream of the discharge; excess lifetime risk to an individual exposed to predicted levels of chloroform in the river range from 5 x 10(-7) to above 10(-6), a degree of risk that is close to levels of concern to regulatory agencies.