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The acute toxicity of major ion salts to Ceriodaphnia dubia: I. Influence of background water chemistry
Citation:
Mount, Dave, R. Erickson, T. Highland, R. Hockett, D. Hoff, T. Norberg-King, K. Peterson, Z. Polaske, AND S. Wisniewski. The acute toxicity of major ion salts to Ceriodaphnia dubia: I. Influence of background water chemistry. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 35(12):3039-3057, (2016).
Impact/Purpose:
This paper is the first in a series regarding the toxicity of major geochemical ions to aquatic organisms. It covers initial efforts regarding how background water chemistry affects the acute toxicity of individual major ion salts to one test species, the principal findings being that calcium affects the toxicity of sodium and magnesium salts and sodium affects the toxicity of potassium salts. This research also demonstrated that there are multiple mechanisms of toxicity among the different ions, notably that cation-specific toxicity results from potassium, magnesium, and calcium salts and that a more general, multi-ion toxicity is evident in the toxicity of sodium salts. This work furthermore demonstrated the importance of relating toxicity to chemical activities, rather than mass concentrations of ions. This has considerable relevance to regulation of these ions, specifically that prediction of effects are most accurate when a function of the composition of the ion mixture, rather than being based on a single ion or on a single value for any measure of ion concentration. Combined with ongoing efforts regarding ion toxicity for more complex, field-relevant mixtures and for other endpoints and test species, this work will support more appropriate aquatic risk assessments for major ions.
Description:
The ions Na+, K+, Ca2+, Mg2+, Cl-, SO42-, and HCO3-/CO32- (referred to as “major ions”) are present in all fresh waters and are physiologically required by aquatic organisms, but can be increased to harmful levels by a variety of anthropogenic activities that speed geochemical weathering or otherwise introduce or concentrate ions. While toxicity of these ions to aquatic organisms has been previously shown, it is also known that their toxicity can vary depending on the concentrations of other co-occurring anions, and understanding these relationships is key to predicting toxicity and establishing appropriate environmental limits. In this paper we conduct a series of experiments with Ceriodaphnia dubia to evaluate the acute toxicity of all twelve major ionsalts (pairing one of the cations with one of the anions) and to determine how toxicity of these salts varies as a function of background water chemistry. All salts except CaSO4 and CaCO3 were acutely toxic to C. dubia below saturation, with the lowest LC50s found for K salts. Of the remaining salts, all but CaCl2 showed some degree of decreased toxicity as the ionic content of the background water increased. Experiments that independently varied Ca:Mg ratio, Na:K ratio, Cl:SO4 ratio, and alkalinity/pH were used to show that Ca concentration was the primary factor influencing the toxicities of Na and Mg salts. In contrast, the toxicities of K salts were primarily influenced by the concentration of Na. These experiments also indicated multiple mechanisms of toxicity and suggested some important aspects of dosimetry, the toxicities of K, Mg, and Ca salts being best related to the chemical activity of the cation, while the toxicities of Na salts involved all the ions and were correlated with osmolarity. Understanding these basic relationships between major ion toxicity and background water chemistry should aid in the development of sensible risk assessment and regulatory standards for waters subject to increased ionic concentrations.
