3种毒性预测模型在镉对小麦根毒性预测中的应用及比较

摘要

Some toxicity models based on metal speciation,have been widely applied in aquatic and terrestrial ecosystem,such as Free Ion Activity Model (FIAM),Biotic Ligand Model (BLM),and Gouy-Chapman-Stem Model (GCSM).However,the systematic comparison of these models was deficient.In this study,cadmium (Cd) toxicity to wheat root elongation was tested using hydroponic experiments.The three models were developed by nonlinear firing of the experimental data.The models were compared using three different endpoints:relative root elongation (RE),Cd concentration on the root surfaces,and the uptake of Cd in wheat roots.In addition,citric acid (CA) and malate acid (MA) were used to investigate the effect of organic ligands to Cd toxicity.Results showed that Ca2+ and H+ were competitive cations to Cd2+,while Na+,K+ and Mg2+ were not.BLM performed the best prediction for the three endpoints because it considered both free ion activity and competition effects in the solution.FIAM and GCSM only considered the free ion activity and ignored the effect of competitive effect of Ca2+ and H+,thus their prediction was worse than BLM.Results also showed that despite the presence of organic ligands (CA or MA) lowered the activity of free Cd,the toxicity remained the same.It suggested that Cd toxicity to wheat was mainly controlled by the diffusion process rather than internalization,which might be why the FIAM and GCSM performances were not as good as BLM.Results found in this study can provide better understanding of Cd toxicity model in terrestrial system.%一些基于重金属形态的生物毒性机理模型被广泛应用于水体和陆生生态系统,例如:自由离子活度模型(FIAM)、生物配体模型(BLM)和生物膜电势斯特恩双电层模型(GCSM),但不同模型的应用效果之间还缺乏系统比较.本研究选取小麦作为受试生物,采用水培实验进行了镉对小麦根伸长的毒性测试,通过数据分析软件对实验数据进行非线性拟合,分别建立了3种模型,并从根毒性、根表面吸附镉和根中富集镉3个方面对3个模型的预测能力进行了比较.除此之外,选取苹果酸和柠檬酸2种有机配体,研究了配体对镉生物毒性的影响.结果表明,Ca2+和H+对Cd的根毒性存在竞争效应,而Mg2+、K+和Na+未发现竞争效应.由于BLM模型同时考虑了镉的自由离子态浓度和竞争离子的影响,在预测镉对杨麦13号根毒性和生物体内富集量时效果最好.而FIAM和GCSM模型由于计算中仅考虑了离子活度的影响,缺乏对竞争离子保护效应的考虑,因此预测效果相对较差;此外,Cd对小麦根毒性的主要受扩散过程控制,而非跨膜过程,这可能也是FIAM模型和GCSM模型预测不佳的原因之一.同时结果还发现有机配体存在时尽管降低了溶液中镉的离子活度,但未显著影响镉毒性,进一步证明了扩散过程对Cd毒性的影响.以上结果为评价和预测镉的陆生生态毒性提供了基础数据和模型依据.