This effort involved intensive chronic toxicity testing of major ion salts (comprised of Na, K, Ca, Mg, Cl, SO4, HCO3/CO3) with the cladoceran, Ceriodaphnia dubia, a species known to be relatively sensitive to ion enrichment. This is the fourth in a series of manuscripts discussing the sensitivity of this species to major ions, with a specific focus of determining whether the principles governing acute response of this species to major ions also predict chronic responses. Results show this to be true, with acute-chronic ratios that are fairly consistent across different major ions, and responses to binary mixtures that show the same types of joint toxicity profiles as was observed previously for acute toxicity of major ions to this species. Mathematical models describing the response of these organisms were developed to predict the toxicity of major ion mixtures based on either chemical activity or chemical concentrations of ions in the mixture. These models showed good agreement with independent literature data on the chronic toxicity of major ion salts or ion mixtures to C. dubia. The datasets associated with this effort provide effect concentrations (EC20 and EC50) for 60 chronic toxicity tests conducted as part of this research, along with literature data extracted for comparison with model predictions. Data generated in this effort will inform efforts by OW, Regions, States, and Tribes to develop water quality standards/criteria for specific major ions (e.g., Cl, SO4). Perhaps more importantly, it provides part of the necessary scientific underpinning for developing standards/criteria that are sensitive to the specific composition of different sources of ion enrichment (e.g., produced water, mine drainage, irrigation return, industrial/municipal effluents) and can therefore support development of robust, integrated assessment tools.

This dataset is associated with the following publication: Mount, D., R. Erickson, B. Forsman, T. Highland, R. Hockett, D. Hoff, C. Jenson, and T. Norberg-King. Chronic toxicity of major ion salts and their mixtures to Ceriodaphnia dubia. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, USA, 38(4): 769-783, (2019).