Schwab A P, He Yinghong, Banks M K
Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA.
Chemosphere. 2005 Nov;61(6):856-66. doi: 10.1016/j.chemosphere.2005.04.098. Epub 2005 Jun 24.
Organic acids are commonly produced and exuded by plant roots and soil microorganisms. Some of these organic compounds are effective chelating agents and have the potential to enhance metal mobility. The effect of citrate and salicylate on the leaching of lead in soil was investigated in a laboratory experiment. In short-term batch experiments, adsorption of lead to soil was slightly enhanced with increasing salicylate concentration (500-5000 microM) but decreased significantly in the presence of citrate. These observations suggested that citrate may enhance Pb leaching, but this was not observed in the column study. Soluble Pb in the presence and absence citrate or salicylate (up to 5000 microM) was added to soil columns at a moderate flow rate, but no Pb was observed to emerge from the soil in any of the soil columns. Rapid biodegradation of citrate in soil eliminated potential complexing ability. Breakthrough of Pb from soil was noted only when using small columns at high flow rates (>20 pore volumes per day). Under these conditions of physical and chemical non-equilibrium, citrate was not degraded and significantly enhanced Pb mobility. As in the batch adsorption experiments, the presence of salicylate reduced Pb leaching. Considering the extreme conditions required to induce Pb leaching, it is likely that Pb will remain relatively immobile in soil even in the presence of a strong complexing agent such as citrate.
有机酸通常由植物根系和土壤微生物产生并分泌。其中一些有机化合物是有效的螯合剂，具有增强金属迁移性的潜力。在一项实验室实验中研究了柠檬酸盐和水杨酸盐对土壤中铅淋溶的影响。在短期批量实验中，随着水杨酸盐浓度（500 - 5000微摩尔）的增加，铅在土壤上的吸附略有增强，但在柠檬酸盐存在的情况下显著降低。这些观察结果表明柠檬酸盐可能会增强铅的淋溶，但在柱实验中未观察到这种情况。以适中流速将存在和不存在柠檬酸盐或水杨酸盐（高达5000微摩尔）情况下的可溶性铅添加到土壤柱中，但在任何土壤柱中均未观察到有铅从土壤中流出。土壤中柠檬酸盐的快速生物降解消除了其潜在的络合能力。仅在使用小柱且流速较高（每天>20孔隙体积）时才注意到铅从土壤中的穿透。在这些物理和化学非平衡条件下，柠檬酸盐未被降解并显著增强了铅的迁移性。与批量吸附实验一样，水杨酸盐的存在减少了铅的淋溶。考虑到诱导铅淋溶所需的极端条件，即使在存在强络合剂如柠檬酸盐的情况下，铅在土壤中可能仍相对不易迁移。
