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Chronic toxicity of major ion salts and their mixtures to Ceriodaphnia dubia
Citation:
Mount, Dave, 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, 38(4):769-783, (2019). https://doi.org/10.1002/etc.4346
Impact/Purpose:
The manuscript describes results of intensive chronic toxicity testing of major ion salts (comprised of Na, K, Ca, Mg, Cl, SO4, HCO3/CO3) to 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, and application of an acute-chronic ratio of 2 (for EC50) or 2.8 (for EC20) applied to the previously developed model for acute toxicity can predict chronic responses within the limits of inter-test variability. 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 be used to develop, robust, integrated standards.
Description:
The toxicity of waters with sufficiently elevated concentrations of major geochemical ions (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, and HCO3-/CO32-) to aquatic life is well demonstrated, though the majority of such studies have focused on acute toxicity. To support prediction of chronic toxicity, we conducted 60 chronic toxicity tests of individual and mixed ion salts with the cladoceran, Ceriodaphnia dubia, with the goal of quantitatively evaluating whether the toxicological behavior of major ions observed for acute responses of this species are applicable to chronic responses. These tests indicate that chronic responses paralleled those demonstrated previously for acute exposure, specifically: 1) similar relative toxicity of individual ion salts; 2) Na salts showing similar potency when expressed as osmolarity; 3) cation-specific toxicity for salts of Mg, Ca, and K; 4) amelioration of toxicity of Na and Mg salts when Ca activity is increased at sub-toxic concentrations; 5) additive behavior for salt mixtures sharing a common cation; 6) independent behavior for salt mixtures with dissimilar cations, except Mg/Ca mixtures which appeared additive; and 7) expressing exposure on the basis of chemical activity rather than total concentration improved coherence of data across different ion mixtures. Average acute-chronic ratios (acute LC50:chronic ECX) of 2.0 for LC50/EC50 and 2.8 for LC50/EC20 were applied to acute toxicity models published previously, and were able to predict chronic toxicity within the range of inter-test variability. As these models are informed by a wide range of ion mixtures, they should provide robust assessment tools for waters with a variety of ionic compositions.
