陆地生物配体模型（t-BLM）初探：镁离子降低铜离子对小麦根的毒性

生物配体模型(BLM)同时考虑了水中金属离子的化学形态以及阳离子与金属离子在生物配体(BL)上的竞争对其毒性的影响,能成功预测水体金属的生物毒性/有效性.最近,BLM呈现出向土壤环境中拓展的趋势,发展能预测重金属对土壤生物毒性的陆地生物配体模型(t-BLM)正成为最新的国际研究热点.论文模拟土壤溶液,以土壤溶液中的主要阳离子Mg2+为例,通过单因素浓度控制-恒pH营养液培养-陆生植物根伸长抑制试验,定量探讨了不同浓度Mg2+存在下,铜离子(Cu2+)对小麦(Triticum aestivum)根的毒性.结果表明,Mg2+浓度升高显著减弱了Cu2+对小麦根的毒性,即呈现出保护效应.证实陆地生态系统中也存在阳离子对重金属植物毒性的保护效应,支持了BLM中阳离子和重金属离子在生物配体上存在竞争结合的假设,即BLM概念适用于陆生植物.定量分析表明,小麦根生长抑制的毒性效应指标EC50(以自由铜离子活度表示)与自由镁离子活度间存在良好的相关性,线性回归方程为:pEC50(Cu2+)=-0.36(Mg2+)+6.47(r2=0.9976),Mg2+对Cu2+毒性的影响强度可以通过该方程进行预测.论文积累了重金属铜对典型陆生受试植物小麦的毒性数据,探讨了t-BLM的构建方法学,并为其发展提供了思路.联合了土壤理化性质、金属形态及生物积累和毒性效应的t-BLM,将提供一个环境风险评价和制定土壤质量标准的新工具.

Development of a Terrestrial Biotic Ligand Model (t-BLM ): Alleviation of the Rhizotoxicity of Copper to Wheat by Magnesium

By incorporating metal chemical speciation and the protective effects of competing cations on the BL, the Biotic Ligand Model(BLM)had been developed to predict aquatic metal bioavailability and toxicity. Recently, the BLM concept was applied to the soil environment. Developing the terrestrial biotic ligand model(t-BLM)which can effectively predict the ecotoxicity of heavy metals to soil organisms became a hot issue. At different concentrations of magnesium, which is one of the major cations in soil solution, copper toxicity affecting root growth of wheat(Triticum aestivum)was quantitatively discussed, by independent factor controlling-nutrient solution culture with constant pH-root elongation inhibition test of terrestrial plant. Results showed that higher concentrations of Mg2 decreased the toxicity of Cu2 to the wheat root significantly, which confirmed that the protective effects of cations to the plant metal toxicity exists in the terrestrial ecosystem, and held out the BLM hypothesis that cations compete with metal ion for the bound to the BL, i.e. the BLM concept applies to the terrestrial plants. Quantitative analysis showed a good relationship between the toxicity response index EC50(expressed as free copper ion activities) and free magnesium ion activities: pEC50(Cu2 )= -0.36(Mg2 ) 6.47(r2 = 0.9976),which meant the extent of magnesium influencing copper toxicity could be predicted by the equation. The conceptual model and modeling methodology of the t-BLM were discussed too. The t-BLM which combined the soil physicochemical property, metal speciation and organisms bioaccumulation/toxicity response, might provide a new tool to develop the more rational soil quality criteria and risk assessment of heavy metals.