Cheng Tao, Allen Herbert E
Department of Civil and Environmental Engineering, Center for the Study of Metals in the Environment, University of Delaware, Newark, 19716, USA.
J Environ Manage. 2006 Aug;80(3):222-9. doi: 10.1016/j.jenvman.2005.09.007. Epub 2005 Dec 9.
The zinc binding characteristics of natural organic matter (NOM) from several representative surface waters were studied and compared. NOM samples were concentrated by reverse osmosis. The samples were treated in the laboratory to remove trace metals. Square wave anodic stripping voltammetry (SWASV) was used to study zinc complexing properties of those NOM samples at fixed pH, ionic strength, and dissolved organic carbon (DOC) concentrations. Experimental data were compared to the predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. At the same pH, ionic strength, and temperature, the zinc titration curves for NOM samples from different surface water sources tested in our study almost overlapped each other, indicating similarity in zinc binding properties of the NOM. A discrete two-site model gave good fits to our experimental titration data. Non-linear fitting by FITEQL 4.0 shows that the conditional zinc binding constants at the same pH are similar for NOM from different sources, indicating that zinc complexation characteristics of the NOM used in our study do not depend on their origin and one set of binding parameters can be used to represent Zn-NOM complexation for NOM samples from those different surface water sources representing geographically diverse locations. In addition, the total ligand concentrations (L(1,T), L(2,T), and L(T)) of all NOM show no observable gradation with increasing pH (L(1,T)=2.06+/-0.80 mmol/g carbon; L(2,T)=0.12+/-0.04 mmol/g carbon; L(T)=2.18+/-0.78 mmol/g carbon), while the conditional binding constants of zinc by NOM (logK(ZnL)(c)) show a linear increase with increasing pH(logK(1)(c)(pH=6.0)=4.69+/-0.25; logK(1)(c)(pH=7.0)=4.94+/-0.10; logK(1)(c)(pH=8.0)=5.25+/-0.006; logK(2)(c)(pH=6.0)=6.29+/-0.13; logK(2)(c)(pH=7.0)=6.55+/-0.08; logK(2)(c)(pH=8.0)=6.86+/-0.023) with a slope of ca. 0.28, indicating the zinc-NOM complexes become more stable at higher pH. The WHAM VI predicted free zinc ion activities at high zinc concentrations agree with our experimental results at pH 6.0, 7.0, and 8.0. However, the zinc binding of these NOM samples is over estimated by WHAM VI at zinc concentrations below 10(-6) M at pH 8.0.
研究并比较了几种代表性地表水的天然有机物（NOM）的锌结合特性。通过反渗透对NOM样品进行浓缩。在实验室对样品进行处理以去除痕量金属。采用方波阳极溶出伏安法（SWASV）研究这些NOM样品在固定pH值、离子强度和溶解有机碳（DOC）浓度下的锌络合特性。将实验数据与温德米尔腐殖质水模型（WHAM）第六版的预测结果进行比较。在相同的pH值、离子强度和温度下，我们研究中测试的不同地表水来源的NOM样品的锌滴定曲线几乎相互重叠，表明NOM的锌结合特性具有相似性。一个离散的双位点模型很好地拟合了我们的实验滴定数据。FITEQL 4.0的非线性拟合表明，不同来源的NOM在相同pH值下的条件锌结合常数相似，这表明我们研究中使用的NOM的锌络合特性不取决于其来源，一组结合参数可用于表示来自那些代表不同地理位置的不同地表水来源的NOM样品的锌-NOM络合作用。此外，所有NOM的总配体浓度（L(1,T)、L(2,T)和L(T)）在pH值升高时没有明显的梯度变化（L(1,T)=2.06±0.80 mmol/g碳；L(2,T)=0.12±0.04 mmol/g碳；L(T)=2.18±0.78 mmol/g碳），而NOM对锌的条件结合常数（logK(ZnL)(c)）随着pH值的升高呈线性增加（logK(1)(c)(pH=6.0)=4.69±0.25；logK(1)(c)(pH=7.0)=4.94±0.10；logK(1)(c)(pH=8.0)=5.25±0.006；logK(2)(c)(pH=6.0)=6.29±0.13；logK(2)(c)(pH=7.0)=6.55±0.08；logK(2)(c)(pH=8.0)=6.86±0.023），斜率约为0.28，表明锌-NOM络合物在较高pH值下变得更稳定。WHAM VI预测的高锌浓度下的游离锌离子活性与我们在pH值为6.0、7.0和8.0时的实验结果一致。然而，在pH值为8.0时，锌浓度低于10^(-6) M时，这些NOM样品的锌结合被WHAM VI高估。
