基于生物配体模型(BLM)研究土壤铅锌的生物毒性及其影响因素

Human activities (such as mining and smelting, heavy metals from atmospheric deposition, utilization of sewage sludge, soil application of fertilizer, and so on) lead to single and combined pollution of zinc and lead more and more severity. Soil contaminated by zinc and lead will affect the growth of crops, microbe and animal in the farmland ecosystem, or even a serious threat to human health. The project discuss the key issues of the quantitative relation between soil lead (or zinc, or combined pollution of zinc and lead) availability and plant toxicity (or microbial toxicity). The effect of single and combined pollution of zinc and lead on biological toxicity will be studied by using plant roots growth inhibition assay and Substrate-Induced Nitrification (SIN). Focus on: (1) the main control factors of soil Pb, Zn and their combined pollution on plant toxicity and microbial toxicity; (2) the dose-response relationship between soil lead (or zinc, or combined pollution of zinc and lead) and biological toxicity; (3) the influence mechanism of soil pH value, DOM, CEC and other factors on the biological toxicity under lead, zinc and their combined pollution; (4) constructing the terrestrial biotic ligand model (tBLM) based on ecological and toxicological mechanism. Our study will reveal the effect rule of soil lead, zinc and their combined pollution on the biological toxicity, and will provide a scientific basis for reasonable establishment soil environmental quality standard, soil heavy metal pollution evaluation and protection of ecological environment.

由于人为因素的影响（如矿产开采和冶炼等）导致土壤铅、锌及其复合污染不断加重，影响农田生态系统中作物、微生物和动物的生长发育，甚至严重威胁人类的身体健康。本项目围绕土壤铅、锌有效性及其复合污染与植物毒性、微生物毒性量化关系的关键问题，采用植物根生长抑制法和基质诱导硝化法（Substrate-Induced Nitrification, SIN）研究土壤铅锌污染对生物毒性的影响。重点研究：（1）土壤铅、锌及其复合污染植物毒性、微生物毒性的主控因子；（2）土壤铅、锌及其复合污染浓度与生物毒性的剂量-效应关系；（3）土壤pH值、DOM、CEC等因素变化对铅、锌及其复合污染生物毒性的影响机制；（4）构建基于生态毒理机制的陆地生物配体模型（tBLM）。从而揭示土壤铅、锌及其复合污染对生物毒性的影响规律，为我国土壤铅、锌环境质量标准的科学制定、土壤铅、锌及其复合污染评价和保护生态环境提供科学依据。

矿产开采和冶炼、工业“三废”排放等原因导致我国农田土壤重金属污染不断加剧。如何科学准确地预测和评价土壤重金属的生物有效性及其生物毒性，是近年来人们关注的热点问题之一。本项目采用基质诱导硝化法和植物根生长抑制法研究土壤铅锌污染对生物毒性的影响。基于基质诱导硝化测试，获得中国17种土壤的外源Pb、Zn的剂量-效应关系和毒性阈值ECx。多元线性回归分析表明，土壤pH和有机碳含量(OC)是影响土壤Zn毒性的主控因子，土壤pH和阳离子交换量（CEC）是土壤Pb毒性的主控因子。淋洗显著降低了土壤外源Pb、Zn的毒性。基于土壤孔隙水的化学性质，研究中国12种土壤外源Pb、Zn及联合毒性效应。结果表明，12种土壤的EC50（Zn2+）在0.01～439.07µmol•L-1之间，EC50（Pb2+）在0.00～6.04 µmol•L-1之间；在Pb-Zn复合体系中，6种土壤随着Pb2+浓度的增大，Zn2+的毒性逐渐增大，而5种土壤在低的Pb2+浓度梯度下，Zn2+的毒性先减小，而后随着Pb2+浓度的增大而增大，表明高浓度Pb对Zn的毒性有促进作用；利用毒性单位经验模型计算了混合体系的EC50mix值，Pb-Zn的EC50mix=0.70 TU<1 TU，表明Pb-Zn的联合毒性效应为协同作用。采用水培实验研究溶液pH值及主要阳离子对水稻铅和锌的毒性的影响，建立了铅和锌对水稻毒性的生物配体模型。结果表明，增加Ca2+、Mg2+和H+的活度均可以减缓Pb2+、Zn2+对水稻根伸长的毒性，而增加Na+、K+的活度影响不大。在不同pH条件下，Pb2+都是主要的致毒形态；而在低pH条件(4.5-6.0)下，主要是Zn2+对水稻根伸长产生毒性，在高pH条件(6.5-8.0)下，Zn2+和ZnOH+是主要的致毒形态。根据各平衡常数计算可得，当Pb或Zn结合水稻的生物配体位点分别达到55%或73%之后，水稻根伸长的抑制率达50%（f50=55%，f50=73%）。铅锌复合毒性研究结果表明，BLM-fmix方法对铅锌毒性的预测效果最好，说明铅和锌作用于相同的生物位点上，具有相同的行为机制。研究中建立的生物配体模型预测的EC50(Pb2+)或EC50(Zn2+)值均在实测值EC50的2倍变化范围之内，表明生物配体模型可以有效地预测铅锌对水稻根伸长的急性毒性。