铜对大麦(Hordeum vulgare)的急性毒性预测模型——生物配体模型

Development of Biotic Ligand Model (BLM) predicting copper acute toxicity to barley (Hordeum vulgare)

采用水培的方法研究了Ca2+、Mg2+、K+、Na+和pH对大麦铜急性毒性的影响程度,并建立了一种用于预测铜对大麦急性毒性的生物配体模型(BLM).结果表明,高活度Mg2+(1.21mmol.L-1和1.65mmo.lL-1)显著增加了大麦根伸长的半抑制浓度EC50(Cu2+)(以自由Cu2+活度表示),而Ca2+、K+、Na+对EC50(Cu2+)的影响没有达到显著水平.培养液中铜的形态分析和相关分析表明,pH值通过改变羟基铜(CuOH+)的含量而影响铜的毒性.根据生物配体模型理论,估计了Cu2+、Mg2+、CuOH+和生物配体的络合平衡常数,分别为logKCuBL=6.57,logKCuOHBL=7.03,logKMgBL=3.00.在此基础上通过计算得出,当50%的大麦根伸长被抑制时需络合66%的生物配体位点,利用上述参数建立的生物配体模型预测的EC50在实测值的2倍范围之内,远远低于仅考虑自由Cu2+毒性的12倍预测范围.结果说明,考虑了Mg2+竞争和CuOH+毒性建立的生物配体模型能够准确地预测铜对大麦的急性毒性.

Copper acute toxicity to barley （Hordeum vulgare） root elongation was studied in culture solutions and modeled by Biotic Ligand Model （BLM）. The effects of Ca^2＋ , Mg^2＋ , Na^＋ , K^＋ ions and pH on the copper toxicity were also examined. The results showed that the toxicity of Cu in culture solutions to barley root elongation decreased with increasing activities of Mg^2＋ in the solutions, while Ca^2 ＋ , Na^＋ , and K^＋ did not significantly affect the Cu toxicity to barley root elongation. From the speciation of copper in solution and linear regression analysis, it suggested that the formation of CuOH^＋ in high pH range from 7.0 to 8.0 should be considered as toxic species of Cu in solutions. The stability constants for the binding of Cu^2＋ , CuOH^ ＋ , and Mg^2＋ to biotic ligands were obtained using biotic ligand model and found to be as follows ： logKC,BL = 6.57, 1ogKC,OHBL = 7.03, 1ogKMgBL = 3.00. Furthermore, on average, about 66% of the biotic ligand sites were occupied by Cu when the barley root elongation was inhibited by 50%. Using these stability constants, the values of ECs0 （the effective concentrations which reduced root elongation by 50% ） were able to be predicted by the BLM in a two folds of deviation from the observed EC50. This prediction is more exact than that only the free Cu^2＋ activity was considered.