Binding constants of divalent mercury (Hg2+) in soil humic acids and soil organic matter

被引:106
作者
Khwaja, AR
Bloom, PR [1 ]
Brezonik, PL
机构
[1] Univ Minnesota, Water Resource Sci Grad Program, St Paul, MN 55108 USA
[2] Univ Minnesota, Dept Soil Water & Climate, St Paul, MN 55108 USA
[3] Univ Minnesota, Dept Civil Engn, Minneapolis, MN 55455 USA
关键词
D O I
10.1021/es051085c
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
Distribution coefficients (K-OC) for Hg2+ binding by IHSS Pahokee peat humic acid (PHA) and humic acids separated from O-horizons and peats in a northern temperate forest were determined using a competitive ligand-exchange method. All measurements were made at low ratios of added Hg2+ to reduced S. The commonly used chelating agents, EGTA and DTPA, were found to be ineffective competitive ligands; thus, we used DL-penicillamine, a synthetic amino acid with a thiol group. Calculated free [Hg2+] at equilibrium is very low, ranging from 10(-26.4) at pH 1.9 to 10(-36.9) at pH 5.8. Corresponding log K-OC values ranged from 22.6 to 32.8. The slope of the plot of pH versus log K-OC was 2.68, suggesting that two or more protons are released when each Hg2+ is bound. This is consistent with binding of Hg2+ to bidentate thiol sites with some participation of a third weak-acid group, presumably a thiol The 1:2 stoichiometry is consistent with X-ray spectroscopy data for Hg2+ bound to HA and with other pH-dependency results showing release of two protons with the binding of each Hg2+. Our K-OC values are much greater than indicated by the data from most previous studies.
引用
收藏
页码:844 / 849
页数:6
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