Department of Soil & Water Sciences, Faculty of Agriculture, University of Kafrelsheikh, 33 516 Kafr El-Sheikh, Egypt.
Adv Colloid Interface Sci. 2013 Dec;201-202:43-56. doi: 10.1016/j.cis.2013.10.005. Epub 2013 Oct 16.
Knowledge about the behavior and reactions of separate soil components with trace elements (TEs) and their distribution coefficients (Kds) in soils is a key issue in assessing the mobility and retention of TEs. Thus, the fate of TEs and the toxic risk they pose depend crucially on their Kd in soil. This article reviews the Kd of TEs in soils as affected by the sorption system, element characteristics, and soil colloidal properties. The sorption mechanism, determining factors, favorable conditions, and competitive ions on the sorption and Kd of TEs are also discussed here. This review demonstrates that the Kd value of TEs does not only depend on inorganic and organic soil constituents, but also on the nature and characteristics of the elements involved as well as on their competition for sorption sites. The Kd value of TEs is mainly affected by individual or competitive sorption systems. Generally, the sorption in competitive systems is lower than in mono-metal sorption systems. More strongly sorbed elements, such as Pb and Cu, are less affected by competition than mobile elements, such as Cd, Ni, and Zn. The sorption preference exhibited by soils for elements over others may be due to: (i) the hydrolysis constant, (ii) the atomic weight, (iii) the ionic radius, and subsequently the hydrated radius, and (iv) its Misono softness value. Moreover, element concentrations in the test solution mainly affect the Kd values. Mostly, values of Kd decrease as the concentration of the included cation increases in the test solution. Additionally, the Kd of TEs is controlled by the sorption characteristics of soils, such as pH, clay minerals, soil organic matter, Fe and Mn oxides, and calcium carbonate. However, more research is required to verify the practical utilization of studying Kd of TEs in soils as a reliable indicator for assessing the remediation process of toxic metals in soils and waters.
关于痕量元素 (TEs) 与土壤中各部分成分的行为和反应及其在土壤中的分配系数 (Kd) 的知识，是评估 TEs 迁移和保留能力的关键问题。因此，TEs 的命运及其造成的毒性风险在很大程度上取决于其在土壤中的 Kd 值。本文综述了土壤中 TEs 的 Kd 值受吸附体系、元素特性和土壤胶体特性的影响。还讨论了 TEs 吸附和 Kd 值的吸附机制、决定因素、有利条件和竞争离子。本文综述表明，TEs 的 Kd 值不仅取决于无机和有机土壤成分，还取决于所涉及元素的性质和特征及其对吸附位点的竞争。TEs 的 Kd 值主要受单独或竞争吸附体系的影响。一般来说，竞争体系中的吸附低于单金属吸附体系。与 Cd、Ni 和 Zn 等移动元素相比，Pb 和 Cu 等强烈吸附的元素受竞争的影响较小。土壤对元素的吸附偏好可能归因于：(i) 水解常数，(ii) 原子量，(iii) 离子半径，随后是水合半径，和 (iv) 其 Misono 软度值。此外，测试溶液中元素的浓度主要影响 Kd 值。通常，随着测试溶液中包括的阳离子浓度的增加，Kd 值会降低。此外，TEs 的 Kd 值受土壤的吸附特性控制，如 pH 值、粘土矿物、土壤有机质、Fe 和 Mn 氧化物以及碳酸钙。然而，需要进一步研究以验证在土壤中研究 TEs 的 Kd 值作为评估土壤和水中有毒金属修复过程的可靠指标的实际应用。
