Clifford Matthew, McGeer James C
Department of Biology, Wilfrid Laurier University, Waterloo, ON. N2L 3C5, Canada.
Aquat Toxicol. 2009 Jan 18;91(1):26-32. doi: 10.1016/j.aquatox.2008.09.016. Epub 2008 Oct 22.
The goal of this study was to develop a biotic ligand model (BLM) for the acute toxicity of zinc to the Daphnia pulex in soft water. In different tests Ca (as CaSO(4)), Na (as NaCl), Mg (as MgSO(4)), K (as KCl), pH (using the buffer 3-(N morpholino)-propanesulphonic acid (MOPS)) and dissolved organic carbon (DOC) were altered to determine possible effects on the 48h EC50 for Zn. Increases in waterborne Ca(2+) had a protective effect on Zn toxicity, suggesting that this ion competes with Zn and that they share a common site of biological uptake. Increased waterborne Mg(2+) also reduced Zn toxicity, but to a lesser degree compared with Ca(2+). No significant effects of other cations on EC50 for Zn were observed, indicating that the toxicity of Zn in D. pulex is not linked to Na(+) and K(+). Increasing DOC concentrations resulted in higher EC50 values for Zn due to the complexation of Zn by organic matter in solution and the resulting reduction of free Zn(2+) ion concentrations. Tests to characterize the effect of pH on Zn toxicity showed a small rise in EC50 values between pH 6.3 and 7.1 and no further change as pH was increased to 8.0. Two existing BLM implementations for acute Zn effects on D. magna were tested to determine their applicability to D. pulex in soft water. The existing models underestimated the protective effect of Ca(2+) and Mg(2+) but accurately predict the effects of DOC. A modified BLM, with revised equilibrium constants for competitive cation effects was developed. This study shows that the acute effects of Zn on D. pulex in soft water can be characterized and incorporated into a predictive BLM.
本研究的目的是建立一个生物配体模型（BLM），用于预测软水中锌对蚤状溞的急性毒性。在不同的试验中，改变了钙（以CaSO₄形式）、钠（以NaCl形式）、镁（以MgSO₄形式）、钾（以KCl形式）、pH值（使用3-(N-吗啉代)丙烷磺酸（MOPS）缓冲液）和溶解有机碳（DOC），以确定它们对锌的48小时半数有效浓度（EC50）的可能影响。水体中Ca²⁺浓度的增加对锌的毒性具有保护作用，这表明该离子与锌存在竞争关系，且它们共享一个生物摄取的共同位点。水体中Mg²⁺浓度的增加也降低了锌的毒性，但与Ca²⁺相比程度较小。未观察到其他阳离子对锌的EC50有显著影响，这表明蚤状溞中锌的毒性与Na⁺和K⁺无关。由于溶液中的有机物对锌的络合作用以及由此导致的游离Zn²⁺离子浓度降低，DOC浓度的增加导致锌的EC50值升高。表征pH值对锌毒性影响的试验表明，在pH值6.3至7.1之间EC50值略有上升，而当pH值升高到8.0时没有进一步变化。测试了两种现有的针对大型溞的急性锌效应的BLM模型，以确定它们对软水中蚤状溞的适用性。现有模型低估了Ca²⁺和Mg²⁺的保护作用，但准确预测了DOC的影响。开发了一个修正的BLM模型，对竞争性阳离子效应的平衡常数进行了修订。本研究表明，软水中锌对蚤状溞急性毒性效应可以得到表征，并纳入一个预测性的BLM模型中。
