An emerging Multi-Ion Toxicity (MIT) model for assessment of environmental salt pollution is based on the premise that major ion toxicity to aquatic organisms is related to a critical disturbance of the trans-epithelial potential across the gills (ΔTEP), which can be predicted by electrochemical theory. However, the model has never been evaluated physiologically. We directly tested key assumptions by examining the individual effects of eight different salts (NaCl, Na₂SO₄, MgCl₂, MgSO₄, KCl, K₂SO₄, CaCl₂, and CaSO₄) on measured TEP in three different fish species (fathead minnow, Pimephales promelas = FHM; channel catfish, Ictalurus punctatus = CC; bluegill, Lepomis macrochirus = BG). A geometric concentration series based on previously reported 96-h LC50 values for FHM was used. All salts caused concentration-dependent increases in TEP to less negative/more positive values in a pattern well-described by the Michaelis-Menten equation. The ΔTEP responses for different salts were similar to one another within each species when concentrations were expressed as a percentage of the FHM LC50. A plateau was reached at or before 100 % of the LC50 where the ΔTEP values were remarkably consistent, with only 1.4 to 2.2-fold variation. This relative uniformity in the ΔTEP responses contrasts with 28-fold variation in salt concentration (in mmol L⁻¹), 9.6-fold in total dissolved solids, and 7.9-fold in conductivity at the LC50. The Michaelis-Menten Km values (salt concentrations causing 50 % of the ΔTEP_max) were positively related to the 96-h LC50 values. ΔTEP responses were not a direct effect of osmolarity in all species and were related to specific cation rather than specific anion concentrations in FHM. These responses were stable for up to 24 h in CC. The results provide strong physiological support for the assumptions of the MIT model, are coherent with electrochemical theory, and point to areas for future research.

用于评估环境盐污染的新兴多离子毒性（MIT）模型基于以下前提：对水生生物的主要离子毒性与鳃跨上皮电位（ΔTEP）的严重干扰有关，这可以通过电化学理论预测。然而，该模型从未经过生理学评估。我们通过检查八种不同盐（NaCl、Na ₂ SO ₄ 、MgCl ₂ 、MgSO ₄ 、KCl、K ₂ SO ₄ 、CaCl ₂和 CaSO ₄ ）对三种不同鱼类测量的 TEP 的单独影响来直接测试关键假设（黑头鲦鱼， Pimephales promelas = FHM；斑点叉尾鮰， Ictalurus punctatus = CC；翻车鱼，Lepomis macrochirus = BG）。使用基于先前报告的 FHM 96 小时 LC50 值的几何浓度系列。所有盐都会导致 TEP 浓度依赖性增加，以米氏方程充分描述的模式减少负值/增加正值。当浓度表示为 FHM LC50 的百分比时，每个物种内不同盐的 ΔTEP 响应彼此相似。在 LC50 的 100% 处或之前达到平台，其中 ΔTEP 值非常一致，仅存在 1.4 至 2.2 倍的变化。 ΔTEP 响应的这种相对均匀性与 LC50 时盐浓度（以 mmol L ^-1为单位）的 28 倍变化、总溶解固体的 9.6 倍变化以及电导率的 7.9 倍变化形成鲜明对比。 Michaelis-Menten Km值（盐浓度导致ΔTEP _max的 50%）与 96 小时 LC50 值正相关。 ΔTEP 响应并不是所有物种中渗透压的直接影响，并且与 FHM 中的特定阳离子而不是特定阴离子浓度相关。这些反应在 CC 中稳定长达 24 小时。结果为 MIT 模型的假设提供了强有力的生理学支持，与电化学理论一致，并指出了未来的研究领域。