Kaschl Arno, Römheld Volker, Chen Yona
Institute of Plant Nutrition (330), University of Hohenheim, 70593 Stuttgart, Germany.
J Environ Qual. 2002 Nov-Dec;31(6):1885-92. doi: 10.2134/jeq2002.1885.
The agricultural practice of amending soils with composted municipal solid waste (MSW) adds significant amounts of organic matter and trace metals, including Cd. Under these conditions, soluble organic complexes of Cd formed in the compost may be more significant than previously thought, due to Cd bioavailability and mobility in the soil environment. To study the relative importance of different types of organic ligands in MSW compost for the binding of Cd, six fractions of the dissolved organic matter (DOM) in addition to humic acid (HA) and fulvic acid (FA) were extracted and their complexation of Cd quantified at pH 7 using an ion-selective electrode (ISE). The highest complexing capacities (CC) for Cd were found for the most humified ligands: HA (2386 micromol Cd g(-1) C of ligand), predialyzed FA (2468 micromol Cd g(-1) C), and HoA, a fulvic-type, easily soluble fraction (1042 micromol Cd g(-1) C). The differences in CC for Cd of the various organic ligands were not directly related to total acid-titratable or carboxylic groups, indicating the importance of sterical issues and other functional groups. The strength of association between Cd and the organic ligands was characterized by calculating stability constants for binding at the strongest sites (pK(int)) and modeling the distribution of binding site strengths. The pK(int) values of the DOM fractions ranged between 6.93 (HiN: polysaccharides) and 8.11 (HiB: proteins and aminosugars), compared with 10.05 for HA and 7.98 for FA. Hence, the highly complex and only partially soluble organic molecules from compost such as HA and FA demonstrated the highest capacity to sequester Cd. However, strong Cd binding of organic ligands containing N-functional groups (HiB) in addition to a high CC of soluble, humified ligands like HoA indicated the relevance of these fractions for the organic complexation of Cd in solution.
用城市固体废弃物（MSW）堆肥改良土壤的农业实践会添加大量有机物质和微量金属，包括镉。在这种情况下，由于镉在土壤环境中的生物有效性和迁移性，堆肥中形成的镉的可溶性有机络合物可能比以前认为的更为重要。为了研究MSW堆肥中不同类型有机配体对镉结合的相对重要性，除了腐殖酸（HA）和富里酸（FA）外，还提取了溶解有机物（DOM）的六个组分，并使用离子选择性电极（ISE）在pH 7下对它们与镉的络合进行了定量。发现最腐殖化的配体对镉具有最高的络合能力（CC）：HA（2386微摩尔镉/克配体碳）、预透析FA（2468微摩尔镉/克配体碳）和HoA，一种富里酸型、易溶组分（1042微摩尔镉/克配体碳）。各种有机配体对镉的CC差异与总酸可滴定或羧基没有直接关系，表明空间问题和其他官能团的重要性。通过计算最强位点结合的稳定常数（pK(int)）并模拟结合位点强度分布，表征了镉与有机配体之间的缔合强度。DOM组分的pK(int)值在从6.93（HiN：多糖）到8.11（HiB：蛋白质和氨基糖）之间，相比之下，HA为10.05，FA为7.98。因此，来自堆肥的高度复杂且仅部分可溶有机分子，如HA和FA，表现出最高的镉螯合能力。然而，除了像HoA这样可溶、腐殖化配体的高CC外，含N官能团的有机配体（HiB）对镉的强结合表明这些组分对于溶液中镉的有机络合具有相关性。
