As part of previous research, the Gas Research Institute, ENSR, and the University of Wyoming developed a series of multi-variate logistic regression equations (called Salinity/Toxicity Relationships or STRs) that predict acute toxicity to three freshwater organisms based on major ion composition. While these equations did an excellent job of representing responses in the laboratory data set on which they were based, their validity and usefulness lay in their-ability to make accurate predictions for independent data sets and real-world samples. Accordingly, the STR equations were applied to a series of data sets from different sources. This exercise shows that the equations generally provide accurate predictions of toxicity, even across waters with very different ionic compositions. STR equations were also able to detect the presence of toxicants other than major ions in the samples. These results indicate that the STR approach will provide a valuable tool for assessing and managing produced waters and other waters with elevated concentrations of dissolved ions.

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