A meta-analysis of acute and chronic major ion toxicity to Ceriodaphnia dubia

Elevated concentrations of major ions can be toxic to aquatic life in freshwater systems. Major ion composition can be variable in natural waters and plays an important role in observed effects. The current state of the art for predicting toxicity to Ceriodaphnia dubia is based on conceptual and predictive mathematical models with two subcomponents, each describing a different toxicity mechanism: a "general ion toxicity submodel" where all ions contribute to toxicity and a "Mg/Ca toxicity submodel," which describes Mg-specific and Ca-specific toxicity. The objectives of this study were to evaluate the impact of variable major ion water composition on toxicity to C. dubia using compiled acute and chronic toxicity data obtained from peer-reviewed and grey literature. The available data include laboratory exposures to well-defined solutions of single salts (e.g., sodium chloride [NaCl]), binary mixtures of various salts (e.g., NaCl + Na2SO4), as well as field samples of high total dissolved solids natural waters or produced waters such as from coal bed methane operations. Most data compiled in this study support the current understanding of major ion toxicity to C. dubia, and the acute and chronic data were well predicted by the general ion toxicity submodel across the entire range of hardness studied. Application of the predictive models to literature data across multiple investigators showed that the models retained excellent predictive ability for acute and chronic toxicity responses for simple and binary salts. However, in the case of a large dataset from a whole effluent testing program from a coal bed methane production operation, the models were less accurate, which may be affected by calcium carbonate solubility and precipitation/dissolution dynamics.