Oil and gas extraction in the Prairie Pothole Region (PPR) of the northern USA has resulted in elevated chloride concentrations in ground and surface water due to widespread contamination with highly saline produced water, or brine. The toxicity of chloride is poorly understood in the high hardness waters characteristic of the region. We evaluated the toxicity of chloride to two endemic species, Daphnia magna (water flea) and Lemna gibba (duckweed), exposed in field-collected waters (hardness ~ 3000 mg/L as CaCO₃) and reconstituted waters (hardness 370 mg/L as CaCO₃) intended to mimic PPR background waters. We also investigated the role of chloride in the toxicity of water reconstituted to mimic legacy brine-contaminated wetlands, using two populations of native Pseudacris maculata (Boreal Chorus Frog). Chloride toxicity was similar in field-collected and reconstituted waters for both D. magna (LC50s 3070–3788 mg Cl⁻¹/L) and L. gibba (IC50s 2441–2887). Although hardness can ameliorate chloride toxicity at low to high hardness, we did not observe additional protection as hardness increased from 370 to ~ 3000 mg/L. In P. maculata exposures, chloride did not fully explain toxicity. Chloride sensitivity also differed between populations, with mortality at 2000 mg Cl⁻/L in one population but not the other, and population-specific growth responses. Overall, these results (1) document toxicity to native species at chloride concentrations occurring in the PPR, (2) indicate that very high hardness in the region’s waters may not provide additional protection against chloride and (3) highlight challenges of brine investigations, including whether surrogate study populations are representative of local populations.

由于高盐度采出水或盐水的广泛污染，美国北部草原坑洼地区 (PPR) 的石油和天然气开采导致地下水和地表水中氯化物浓度升高。在该地区的高硬度水域中，人们对氯化物的毒性知之甚少。我们评估了氯化物对两种特有物种Daphnia magna（水蚤）和Lemna gibba（浮萍）的毒性，暴露在野外采集的水（硬度 ~ 3000 mg/L，以 CaCO ₃计）和复原水（硬度 370 mg/L作为CaCO ₃) 旨在模拟 PPR 背景水。我们还研究了氯化物在重建水的毒性中的作用，以模仿传统的盐水污染湿地，使用两个本地Pseudacris maculata (Boreal Chorus Frog) 种群。D. magna (LC50s 3070–3788 mg Cl ^-1 /L) 和L. gibba (IC50s 2441–2887)在现场收集和复原水中的氯化物毒性相似。虽然硬度可以改善从低硬度到高硬度的氯化物毒性，但我们没有观察到随着硬度从 370 增加到 ~ 3000 mg/L 的额外保护。在P. maculata暴露中，氯化物不能完全解释毒性。不同人群对氯化物的敏感性也不同，死亡率为 2000 mg Cl^- /L 在一个群体中而不是在另一个群体中，以及特定于群体的增长反应。总体而言，这些结果 (1) 记录了 PPR 中氯化物浓度对本地物种的毒性，(2) 表明该地区水域中非常高的硬度可能无法提供针对氯化物的额外保护，以及 (3) 突出了盐水调查的挑战，包括替代研究人群是否代表当地人群。