The acute toxicity of major ion salts to Ceriodaphnia dubia: I. influence of background water chemistry

Abstract

The ions Na , K , Ca , Mg , Cl , SO , and HCO /CO (referred to in the present study as "major ions") are present in all freshwaters and physiologically required by aquatic organisms but can increase to harmful levels from a variety of anthropogenic activities. It is also known that the toxicities of major ion salts can vary depending on the concentrations of other ions, and understanding these relationships is key to establishing appropriate environmental limits. The authors present a series of experiments with Ceriodaphnia dubia to evaluate the acute toxicity of 12 major ion salts and to determine how toxicity of these salts varies as a function of background water chemistry. All salts except CaSO and CaCO were acutely toxic below saturation, with the lowest median lethal concentrations found for K salts. All 10 salts that showed toxicity also showed some degree of reduced toxicity as the ionic content of the background water increased. Experiments that independently varied Ca:Mg ratio, Na:K ratio, Cl:SO ratio, and alkalinity/pH demonstrated that Ca concentration was the primary factor influencing the toxicities of Na and Mg salts, whereas the toxicities of K salts were primarily influenced by the concentration of Na. These experiments also indicated multiple mechanisms of toxicity and suggested important aspects of dosimetry; the toxicities of K, Mg, and Ca salts were best related to the chemical activity of the cation, whereas the toxicities of Na salts also reflected an influence of the anions and were well correlated with osmolarity. Understanding these relationships between major ion toxicity and background water chemistry should aid in the development of sensible risk-assessments and regulatory standards. Environ Toxicol Chem 2016;35:3039-3057. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

The acute toxicity of major ion salts to Ceriodaphnia dubia. III. Mathematical models for mixture toxicity

“…These studies reinforced the findings of Mount et al [1] and provided several new insights. First, the joint toxicities of salts with a shared cation are concentration-additive, suggesting a shared mechanism of action.…”

“…As discussed in previous articles in this series [1,2] and references therein, anthropogenic increases in major geochemical ions (Na þ , K þ , Ca 2þ , Mg 2þ , Cl -, SO 4 2-, and HCO 3 -/CO 3 2-) pose significant and widespread risks to aquatic communities. Because mixtures of these ions in aquatic systems vary widely, adequately characterizing risk requires understanding how the toxicities of these ion mixtures depend on their composition.…”

“…As discussed in the Introduction, Mount et al [1] and Erickson et al [2] reported findings on which a mathematical model for the acute toxicity of major ions to C. dubia can be developed. Based on potency differences and on the existence of both additive and independent joint toxic action among different salts, multiple toxic mechanisms are indicated: a general ion toxicity to which all ions contribute and that is well related to an exposure metric of osmolarity and cation-specific toxicities for K, Mg, and Ca that are best related to an exposure metric of cation activity.…”

“…Modeling this toxicity would be a simple extension of the information in Mount et al [1] and Erickson et al [2] and would involve a third submodel independent of the other two.…”

“…Mount et al [1] investigated the acute toxicity of individual major ion salts to Ceriodaphnia dubia in various dilution waters and reported several outcomes important for describing major ion toxicity. First, toxicity relationships are best understood based on chemical activities rather than concentrations.…”