Pandey A K, Pandey S D, Misra V
Ecotoxicology Section, Industrial Toxicology Research Centre, Lucknow, India.
Ecotoxicol Environ Saf. 2000 Oct;47(2):195-200. doi: 10.1006/eesa.2000.1947.
Humic acid with hydroxyl-, phenoxyl-, and carboxyl-reactive groups can form coordination compounds with metals. The ion-exchange equilibrium method using Dowex AG 50W-X8, 20-25 mesh Na(+) form was used to determine stability constants of complexes formed between humic acid (isolated from the soil) 50-250 microg ( approximately 3x10(-5)-15x10(-5) mol/liter) and metal salts solution 200 microg at pH 3.5. The stability constant (log K) for different metal-humic acid complexes indicated the following order of the stabilities of complexes formed between humic acid and metal ions: Cu>Fe>Pb>Ni>Co>Ca>Cd>Zn>Mn>Mg. The data on stability constants demonstrated substantial deviation from Irwing-Williams series reported for divalent ions. The molar humic acid/metal ratios were also calculated. Some of the factors affecting the stability constants such as cation exchange capacity of humus soil, molecular radius, and molecular surface area of humic molecules were also estimated. The significance of the data to predict the behavior of these complexes in the environment is discussed.
具有羟基、苯氧基和羧基反应基团的腐殖酸可与金属形成配位化合物。采用Dowex AG 50W-X8（20 - 25目，钠型）离子交换平衡法，在pH 3.5条件下，测定了腐殖酸（从土壤中分离得到，50 - 250微克，约3×10⁻⁵ - 15×10⁻⁵摩尔/升）与200微克金属盐溶液形成的配合物的稳定常数。不同金属 - 腐殖酸配合物的稳定常数（log K）表明，腐殖酸与金属离子形成的配合物稳定性顺序为：铜＞铁＞铅＞镍＞钴＞钙＞镉＞锌＞锰＞镁。稳定常数数据表明与报道的二价离子欧文 - 威廉姆斯系列存在显著偏差。还计算了腐殖酸/金属的摩尔比。同时估算了一些影响稳定常数的因素，如腐殖土的阳离子交换容量、腐殖酸分子的分子半径和分子表面积。讨论了这些数据对于预测这些配合物在环境中行为的意义。
