State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China; University of Chinese Academy of Sciences, Beijing 100049, China; Department of Chemistry, University of Buea, P.O. Box 63, Buea, Cameroon.
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Ecotoxicol Environ Saf. 2019 Apr 30;171:790-797. doi: 10.1016/j.ecoenv.2019.01.043. Epub 2019 Jan 17.
The continuous production of low molecular weight (LMW) organic acids by plants and microorganisms coupled with the continuous presence of extracellular polymeric substances (EPS) in soils is a guarantee that the mobility of heavy metals in soils will be controlled. The effects of citrate, oxalate, and EPS on the adsorption of Pb by an acidic Ultisol were studied both as a function of pH and ionic strength. Electrokinetic potential measurements were also employed to observe to what extent each ligand affected the surface charge property of the Ultisol. All the ligands shifted the zeta potential of the Ultisol to the negative direction, implying that the surface charge of the soil became more negative. The effect on the zeta potential of the soil was observed in the order of oxalate ˃ citrate ˃ EPS. The quantity of Pb adsorbed at each pH (3.0-7.0) reflected the corresponding change in the zeta potential as induced by each ligand. The presence of the ligands shifted the isoelectric point of the Ultisol from 4.8 to 3.2 for the EPS system and below 3.0 for the citrate and oxalate systems. More Pb was adsorbed in the presence of oxalate than in the presence of citrate and EPS. The two most outstanding mechanisms that governed the adsorption of Pb by the Ultisol were (1) electrostatic attraction which was supported by the increase in negative zeta potential of the Ultisol and, (2) complexation which was supported by the lesser proportion of Pb adsorbed in the citrate system at higher pH and also by the spectroscopic data for EPS. The combination EPS + citrate + oxalate was more effective in enhancing the adsorption of Pb than the combination EPS + oxalate and EPS + citrate.
植物和微生物不断生产低分子量（LMW）有机酸，以及土壤中不断存在的细胞外聚合物物质（EPS），这保证了土壤中重金属的迁移性将得到控制。研究了柠檬酸、草酸盐和 EPS 对酸性赤红壤吸附 Pb 的影响，其影响因素包括 pH 值和离子强度。还采用动电电位测量来观察每种配体在多大程度上影响赤红壤的表面电荷性质。所有配体都将赤红壤的动电电位移向负向，这意味着土壤的表面电荷变得更负。每种配体对土壤动电电位的影响顺序为草酸盐＞柠檬酸＞EPS。在每个 pH 值（3.0-7.0）下吸附的 Pb 量反映了每种配体诱导的动电电位相应变化。配体的存在将赤红壤的等电点从 EPS 体系的 4.8 移至 3.2，对于柠檬酸和草酸盐体系则移至 3.0 以下。在草酸盐存在下，Pb 的吸附量大于在柠檬酸和 EPS 存在下的吸附量。控制赤红壤吸附 Pb 的两个最突出的机制是（1）静电吸引，这得到赤红壤负动电电位增加的支持，以及（2）络合，这得到在较高 pH 值下柠檬酸体系中 Pb 吸附比例较小以及 EPS 的光谱数据的支持。EPS + 柠檬酸 + 草酸盐的组合比 EPS + 草酸盐和 EPS + 柠檬酸的组合更有效地增强了 Pb 的吸附。
