Citation:

Erickson, R., Dave Mount, T. Highland, R. Hockett, D. Hoff, C. Jenson, T. Norberg-King, AND B. Forsman. Acute Toxicity of Major Geochemical Ions to Fathead Minnows (Pimephales promelas): Part B—Modeling Ion Toxicity. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 41(9):2095-2106, (2022). https://doi.org/10.1002/etc.5389

Impact/Purpose:

Anthropogenic increases of major geochemical (Ca, Mg, Na, K, Cl, SO4, HCO3/CO3) ions in aquatic systems are of widespread concern. Current regulatory efforts generally address just one (Cl) or two (Cl, SO4) of the anions based on single salt toxicity tests, usually with the Na salts, but available evidence indicates that major ion toxicity entails a complex mixture with multiple interactions and mechanisms of action. This paper describes extensive testing to more fully describe the acute toxicity of major ions to juvenile fathead minnows, identifying these various interactions and mechanisms and providing models for predicting the toxicity of a broad range of mixture composition. This should be of benefit to future regulatory efforts regarding major ion risks to freshwater systems.

Description:

Mathematical models are presented for the acute median lethal concentrations of major geochemical ions (Na+, K+, Ca2+, Mg2+, Cl−, SO42−, HCO3−/CO32−) to fathead minnows (Pimephales promelas), based on an extensive series of experiments presented in a companion article. Toxicity relationships across different dilution waters, individual salts, and salt mixtures suggest six independent mechanisms of toxicity to consider in modeling efforts, including Mg/Ca-specific toxicity, osmolarity-related toxicity, SO4-specific toxicity, K-specific toxicity, effects of high pH/alkalinity, and a multiple ion-related toxicity at low Ca distinct from the other mechanisms. Models are evaluated using chemical activity-based exposure metrics pertinent to each mechanism, but concentration-based alternative models that are simpler to apply are also addressed. These models are compared to those previously provided for Ceriodaphnia dubia, and various issues regarding their application to risk assessments are discussed. 

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