Wang Xuedong, Ma Yibing, Hua Luo, McLaughlin Mike J
Ministry of Agriculture Key Laboratory of Plant Nutrition and Nutrient Cycling, The Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, China.
Environ Toxicol Chem. 2009 Mar;28(3):662-7. doi: 10.1897/07-641.1. Epub 2008 Nov 3.
The effect of pH on the acute toxicity of Cu to barley (Hordeum vulgare) root elongation was investigated in solution culture. The results showed that the median effective concentrations (EC50s; i.e., the concentration that reduced root elongation by 50% based on free Cu(2+) activity) were not significantly different in the low-pH range from 4.5 to 6.5, but in the high-pH range from 7.0 to 8.0, a significant effect of pH on EC50s was found. The nonlinear relationship between EC50 and H(+) activity in the present study indicated that the increased toxicity with increasing pH in solution may not be caused by decreasing H(+) competition. When we take account of CuOH(+) activities, a good linear relationship (r(2) > 0.97) between the ratio of CuOH(+) activity to free Cu(2+) activity and acute Cu toxicity to barley root elongation was achieved, which indicated that the observed toxicity in the high-pH range may be caused by CuOH(+) plus free Cu(2+) in solution. Linear-regression analysis suggested CuOH(+) had a greater binding affinity than Cu(2+) at the biotic ligand sites. The logistic dose-response curve showed that expressing the Cu dose as Cu(2+) + 2.92.CuOH(+) improved the data fit significantly compared to consideration of the free Cu(2+) activity only. Thus, our results suggest CuOH(+) was highly toxic to barley root elongation. The enhanced toxicity of CuOH(+) therefore needs to be considered when modeling the effect of pH on Cu toxicity to barley for exposures having pH greater than 6.5.
在溶液培养条件下，研究了pH值对铜对大麦（Hordeum vulgare）根系伸长的急性毒性的影响。结果表明，在4.5至6.5的低pH范围内，半数有效浓度（EC50，即基于游离Cu(2+)活性使根系伸长降低50%的浓度）无显著差异，但在7.0至8.0的高pH范围内，发现pH值对EC50有显著影响。本研究中EC50与H(+)活性之间的非线性关系表明，溶液中随着pH值升高毒性增加可能并非由H(+)竞争减少所致。当考虑CuOH(+)活性时，CuOH(+)活性与游离Cu(2+)活性的比值与铜对大麦根系伸长的急性毒性之间呈现出良好的线性关系（r(2) > 0.97），这表明在高pH范围内观察到的毒性可能是由溶液中的CuOH(+)和游离Cu(2+)共同引起的。线性回归分析表明，在生物配体位点处，CuOH(+)比Cu(2+)具有更高的结合亲和力。逻辑剂量反应曲线表明，与仅考虑游离Cu(2+)活性相比，将铜剂量表示为Cu(2+) + 2.92·CuOH(+)可显著改善数据拟合度。因此，我们的结果表明CuOH(+)对大麦根系伸长具有高毒性。所以，在模拟pH值对铜对大麦毒性的影响时，对于pH值大于6.5的暴露情况，需要考虑CuOH(+)毒性增强的因素。
