Cloutier-Hurteau Benoît, Sauvé Sébastien, Courchesne François
Department of Geography, Université de Montréal, Québec, Canada H3C 3J7.
Environ Sci Technol. 2007 Dec 1;41(23):8104-10. doi: 10.1021/es0708464.
Metal speciation data calculated by modeling could give useful information regarding the fate of metals in the rhizospheric environment. However, no comparative study has evaluated the relative accuracy of speciation models in this microenvironment. Consequently, the present study evaluates the reliability of free Cu ion (Cu2+) activity modeled by WHAM 6 and MINEQL+ 4.5 for 18 bulk and 18 rhizospheric soil samples collected in two Canadian forested areas located near industrial facilities. The modeling of Cu speciation was performed on water extracts using pH, dissolved organic carbon (DOC), major ions, and total dissolved Al, Ca, Cu, Mg, and Zn concentrations as input data. Four scenarios representing the composition of dissolved organic substances using fulvic, humic, and acetic acids were derived from the literature and used in the modeling exercise. Different scenarios were used to contrast soil components (rhizosphere vs bulk) and soil pH levels (acidic vs neutral to alkaline). Reference Cu2+ activity values measured by an ion-selective electrode varied between 0.39 and 41 nM. The model MINEQL+ 4.5 provided good predictions of Cu2+ activities [root-mean-square residual (RMSR)= 0.37], while predictions from WHAM 6 were poor (RMSR = 1.74) because they overestimated Cu complexation with DOC. Modeling with WHAM 6 could be improved by adjusting the proportion of inert DOC and the composition of DOC (RMSR = 0.94), but it remained weaker than predictions with MINEQL+ 4.5. These results suggested that the discrepancies between speciation models were attributed to differences in the binding capacity of humic substances with Cu, where WHAM 6 appeared to be too aggressive. Therefore, we concluded that chemical interactions occurring between Cu and DOC were key factors for an accurate simulation of Cu speciation, especially in rhizospheric forest soils, where high variation of the DOC concentration and composition are observed.
通过建模计算得到的金属形态数据可以提供有关根际环境中金属归宿的有用信息。然而，尚无比较研究评估过该微环境中形态模型的相对准确性。因此，本研究评估了利用WHAM 6和MINEQL+ 4.5对在加拿大两个靠近工业设施的林区采集的18个表层土壤和18个根际土壤样品中游离铜离子（Cu2+）活性进行建模的可靠性。利用pH值、溶解有机碳（DOC）、主要离子以及总溶解铝、钙、铜、镁和锌浓度作为输入数据，对水提取物进行铜形态建模。从文献中得出了代表使用富里酸、腐殖酸和乙酸的溶解有机物质组成的四种情景，并用于建模练习。使用不同情景来对比土壤成分（根际与表层）和土壤pH水平（酸性与中性至碱性）。通过离子选择性电极测得的参考Cu2+活性值在0.39至41 nM之间变化。模型MINEQL+ 4.5对Cu2+活性给出了良好预测[均方根残差（RMSR）= 0.37]，而WHAM 6的预测较差（RMSR = 1.74），因为它高估了铜与DOC的络合作用。通过调整惰性DOC的比例和DOC的组成，利用WHAM 6进行的建模可以得到改善（RMSR = 0.94），但仍弱于MINEQL+ 4.5的预测。这些结果表明，形态模型之间的差异归因于腐殖物质与铜的结合能力不同，其中WHAM 6似乎过于激进。因此，我们得出结论，铜与DOC之间发生的化学相互作用是准确模拟铜形态的关键因素，尤其是在根际森林土壤中，那里观察到DOC浓度和组成的高度变化。
