Major ion toxicity of six produced waters to three freshwater species: Application of ion toxicity models and tie procedures

Previous research to characterize the acute toxicity of major ions to freshwater organisms resulted in the development of statistical toxicity models for three freshwater species (Ceriodaphnia dubia, Pimephales promelas, and Daphnia magna). These ion toxicity models estimate the toxicity of seven major ions utilizing logistic regression. In this study, the ion toxicity models were used in conjunction with Phase I toxicity identification evaluation (TIE) procedures to evaluate the contribution of major ion toxicity to the total toxicity of six produced water samples ranging in total salinity from 1.7 to 58.1 g/L. Initial toxicities of all six samples were compared to the model predictions. Four produced waters were found to have toxicity consistent with toxicity attributable to major ion concentrations only. Two produced waters were found to exhibit more toxicity than expected from ion concentrations alone. These samples were subjected to Phase I TIE procedures. Toxicities were reduced by specific Phase I TIE manipulations to those predicted by the ion toxicity models. Mock effluents were used to verify the results. The combination of the ion toxicity models with Phase I TIE procedures successfully quantified the toxicity due to major ions in six produced water sample.