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The acute toxicity of major ion salts to Ceriodaphnia dubia: III. Mathematical models for mixture toxicity
Citation:
Erickson, R., Dave Mount, T. Highland, R. Hockett, D. Hoff, C. Jenson, T. Norberg-King, AND K. Peterson. The acute toxicity of major ion salts to Ceriodaphnia dubia: III. Mathematical models for mixture toxicity. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 37(1):247-259, (2018).
Impact/Purpose:
This paper is the third in a series regarding the toxicity of major geochemical ions (Ca+2, Mg+2, Na+, K+, Cl–, SO4–2, and CO3–2/HCO3–) to aquatic organisms. The first paper addressed how background water chemistry affects the acute toxicity of individual major ion salts to C. dubia, while the second paper addressed binary mixtures of salts. These established principles upon which the acute toxicity of any mixture of these salts to C. dubia can be predicted. The current effort developed mathematical models for this and conducted tests of more complex mixtures to test model predictions. These models will support more appropriate assessments for the effects of major ions on this species, and provides a foundation for work with other endpoints and species.
Description:
Based on previous research on the acute toxicity of major ions (Na+, K+, Ca2+, Mg2+, Cl, SO42, and HCO3/CO32) to C. dubia, two mathematical models were developed for predicting the LC50 for any ion mixture, excluding those dominated by K toxicity. One model addresses a mechanism of general ion toxicity to which all ions contribute, and describes osmolarity-based LC50s as a function of Ca activity. The other model addresses a mechanism specifically related to Mg and Ca to apply when such toxicity exceeds general ion toxicity, and describes LC50s as a function of Mg and Ca activities. Both models track well the observed LC50s from past research used in model development, but also successfully predicted LC50s from new toxicity tests on synthetic mixtures of ions emulating chemistries of various ion-enriched effluents and receiving waters. Because of the complexities of relating LC50s to chemical activities and osmolarity, simplified models based directly on ion concentrations were also developed and found to provide useful predictions. These models were also determined to provide better performance than a previously-published model for major ion toxicity.
