Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada.
Aquat Toxicol. 2010 Jun 1;98(1):1-7. doi: 10.1016/j.aquatox.2010.01.001. Epub 2010 Jan 13.
The goal of this study was to develop a biotic ligand model (BLM) to predict the acute toxicity of cadmium to Daphnia pulex. Organisms were cultured in moderately soft water and standard 48h acute toxicity tests were used to determine EC50s in various water chemistries where the effects of Ca(2+), Na(+), Mg(2+), Cl(-), K(+), pH, and two sources of natural organic matter (Suwannee River and Nordic Reservoir) were evaluated. Overall, toxicity responses were consistent with the free-ion activity model and the principles inherent in the BLM. Increases in Ca(2+) resulted in higher EC50s, indicating that Cd(2+) competes with Ca(2+) for uptake at the biotic ligand. Similar cation competition effects were observed when Mg(2+) was varied but with a less pronounced protective effect relative to Ca(2+). Changes in Na(+) and K(+) concentrations had no significant effect on Cd toxicity. EC50 values did not change significantly when pH was adjusted over a range from 8.0 to 6.1. Additions of natural organic matter resulted in elevated dissolved organic carbon (DOC) concentrations that significantly reduced Cd bioavailability via complexation of Cd(2+). An existing biotic ligand model (HydroQual BLM ver 2.2.3) was tested for its ability to predict acute Cd toxicity to D. pulex. Once the BLM was adjusted for the relatively sensitivity of D. pulex the protective effects of Ca and DOC could be predicted reasonably well but other test chemistries did not match with measured EC50s. Binding constants derived from the test results (logK(CaBL) of 4.1, logK(MgBL) of 3.7, logK(HBL) of 6.1 and logK(CdBL) of 7.0) were used to develop a modified BLM for the effects of Cd on D. pulex that accounted for the moderating effect of Ca and Mg on acute toxicity but overestimated the protective effect of DOC.
本研究的目的是开发一个生物配体模型（BLM）来预测镉对大型蚤的急性毒性。在中等硬度的水中培养生物，并使用标准的 48 小时急性毒性测试来确定在不同水化学条件下的 EC50 值，其中评估了 Ca(2+)、Na(+)、Mg(2+)、Cl(-)、K(+)、pH 值以及两种天然有机物源（苏万尼河和北欧水库）的影响。总体而言，毒性反应与自由离子活性模型和 BLM 固有的原理一致。Ca(2+)的增加导致 EC50 值升高，表明 Cd(2+)与 Ca(2+)竞争生物配体的摄取。当 Mg(2+)变化时，观察到类似的阳离子竞争效应，但与 Ca(2+)相比，保护作用不那么明显。Na(+)和 K(+)浓度的变化对 Cd 毒性没有显著影响。当 pH 值在 8.0 到 6.1 之间调整时，EC50 值没有明显变化。添加天然有机物会导致溶解有机碳（DOC）浓度升高，通过与 Cd(2+)络合，显著降低 Cd 的生物利用度。测试了一个现有的生物配体模型（HydroQual BLM ver 2.2.3）预测大型蚤急性 Cd 毒性的能力。一旦 BLM 针对大型蚤的相对敏感性进行了调整，Ca 和 DOC 的保护作用就可以得到很好的预测，但其他测试化学物质与实测 EC50 值不匹配。根据测试结果得出的结合常数（logK(CaBL)为 4.1、logK(MgBL)为 3.7、logK(HBL)为 6.1 和 logK(CdBL)为 7.0）用于开发一个针对 Cd 对大型蚤的影响的改良 BLM，该模型考虑了 Ca 和 Mg 对急性毒性的调节作用，但高估了 DOC 的保护作用。
