Toxicity Identification Evaluation (TIE) of a chemical plant effluent

In the course of conducting a proactive toxicity screening of a chemical plant effluent, currently meeting chemical based discharge requirements, the authors found that the effluent could be chronically toxic to the freshwater invertebrate, Ceriodaphnia dubia. Chronic toxicity was linked to one outfall source, which was acutely toxic when tested individually. Toxicity Identification Evaluation (TIE) techniques implicated Total Dissolved Solids (TDS) and vanadium as the sources of acute toxicity of the individual outfall. Findings of acute studies performed with the single outfall were then verified in chronic studies of composite effluent. The results of the TIE found that TDS was the major contributor to composite effluent toxicity. The role of TDS was quantified through a number of synthetic effluent studies which simulated the TDS of the effluent. The ion-toxicity regression model of Mount and Gulley (1992) was then applied to determine which ion manipulations would most effectively reduce effluent toxicity. Additional toxicity studies were performed using synthetic effluent with manipulated ion content, as per the model output, to verify the effect on toxicity. The role of vanadium in contributing to observed toxicity was also investigated.