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The Acute Toxicity of Major Ion Salts to Ceriodaphnia Dubia. Ii. Empirical Relationships in Binary Salt Mixtures
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. Ii. Empirical Relationships in Binary Salt Mixtures. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 36(6):1525-1537, (2017).
This paper is the second 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 one test species, and suggested multiple mechanisms of toxicity among the different ions. However, this previous work involved the toxicity of just single salts (two ions), whereas risk assessment of these ions generally involves more complex mixtures. The current paper presents a series of binary (two-salt) mixture experiments that further defined the mechanisms of toxicity (cation-specific toxicity of Ca, Mg, and K and a general ion toxicity to which all ions contribute) and provided a basis for describing the toxicity of any mixture of these ions. 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.
Many human activities increase concentrations of major geochemical ions (Na+, K+, Ca+2, Mg+2, Cl, SO42, and HCO3/CO32) in fresh water systems, and can thereby adversely affect aquatic life. Such effects involve several toxicants, multiple mechanisms of toxicity, various ion interactions, and widely varying compositions of ion mixtures across different waterbodies. Previous efforts on the toxicities of individual salts have defined some relationships, but adding single salts to waters results in atypical compositions and does not fully address ion mixture toxicity. To better understand mechanisms and interactions for major ion toxicity, 29 binary mixture experiments, each consisting of 7-8 toxicity tests, were conducted on the acute toxicity of major ion salts and mannitol to Ceriodaphnia dubia. These tests demonstrated multiple mechanisms of toxicity, including 1) a non-specific ion toxicity contributed to by all ions that correlates well with osmolarity and 2) cation-dependent toxicities for K, Mg, and Ca that are best related to chemical activities of these cations. The observed interactions also indicated that these mechanisms primarily operate independently, except for additive toxicity between Mg and Ca dependent toxicities. These mixtures studies also confirmed ameliorative effects of Ca on Na and Mg salt toxicities and of Na on K salt toxicity, and further indicated some lesser ameliorative effects of Ca on K salt toxicity and Mg on Na salt toxicity. However, some of these ameliorative effects are not of practical importance because they depend on unrealistically low concentrations for some ions when other ions are at toxic levels. These results provide a stronger basis for assessing risks from the complex mixtures of ions found in surface waters.