Impellitteri Christopher A, Lu Yuefeng, Saxe Jennifer K, Allen Herbert E, Peijnenburg Willie J G M
Department of Civil and Environmental Engineering, University of Delaware, Newark 19716, USA.
Environ Int. 2002 Nov;28(5):401-10. doi: 10.1016/s0160-4120(02)00065-x.
Eighteen Dutch soils were extracted in aqueous solutions at varying pH. Extracts were analyzed for Cd, Cu, Ni, Pb and Zn by ICP-AES. Extract dissolved organic carbon (DOC) was also concentrated onto a macroreticular resin and fractionation into three operationally defined fractions: hydrophilic acids (Hyd), humic acids (HA) and fulvic acids (FA). In this manner, change in absolute solution concentration and relative percentage for each fraction could be calculated as a function of extraction equilibrium pH. The soils were also analyzed for solid phase total organic carbon and total recoverable metals (EPA Method 3051). Partitioning coefficients were calculated for the metals and organic carbon (OC) based on solid phase concentrations (less the metal or OC removed by the extraction) divided by solution concentrations. Cu and Pb concentrations in solution as a function of extract equilibrium pH are greatest at low and high pH resulting in parabolic desorption/dissolution curves. While processes such as proton competition and proton promoted dissolution can account for high solution metal concentrations at low pH, these processes cannot account for higher Cu and Pb concentrations at high pH. DOC increases with increasing pH, concurrently with the increase in Cu and Pb solution concentrations. While the absolute concentrations of FA and HA generally increase with increasing pH, the relative proportional increase is greatest for HA . Variation in HA concentrations spans three orders of magnitude while FA concentrations vary an order of magnitude over the pH range examined. Correlation analysis strongly suggests that HA plays a major role in increasing the concentration of solution Cu and Pb with increasing pH in the 18 soils studied. The percentage of the OC that was due to FA was nearly constant over a wide pH range although the FA concentration increased with increasing pH and its concentration was greater than that of the HA fraction at lower pH values (pH = 3-5). Thus, in more acidic environments, FA may play a larger role than HA in governing organo-metallic interactions. For Cd, Ni, and Zn, the desorption/dissolution pattern shows high metal solution concentrations at low pH with slight increases in solution concentrations at extremely high pH values (pH>10). The results presented here suggest that the effects of dissolved organic carbon on the mobilization of Cd, Ni, and Zn may only occur in systems governed by very high pH. At high pH, it is difficult to distinguish in this study whether the slightly increased solution-phase concentrations of these cations is due to DOC or hydrolysis reactions. These high pH environments would rarely occur in natural settings.
用不同pH值的水溶液对18种荷兰土壤进行提取。通过电感耦合等离子体发射光谱法（ICP - AES）对提取物中的镉、铜、镍、铅和锌进行分析。提取物中的溶解性有机碳（DOC）也被浓缩到一种大孔网状树脂上，并分成三个操作定义的组分：亲水酸（Hyd）、腐殖酸（HA）和富里酸（FA）。通过这种方式，可以计算出每个组分的绝对溶液浓度和相对百分比随提取平衡pH值的变化。还对土壤的固相总有机碳和总可回收金属进行了分析（美国环境保护局方法3051）。根据固相浓度（减去提取过程中去除的金属或有机碳）除以溶液浓度，计算金属和有机碳（OC）的分配系数。溶液中铜和铅的浓度作为提取平衡pH值的函数，在低pH值和高pH值时最大，从而产生抛物线形的解吸/溶解曲线。虽然质子竞争和质子促进溶解等过程可以解释低pH值时溶液中高金属浓度的现象，但这些过程无法解释高pH值时铜和铅浓度更高的现象。DOC随着pH值的升高而增加，同时铜和铅的溶液浓度也增加。虽然FA和HA的绝对浓度通常随着pH值的升高而增加，但HA的相对比例增加最大。HA浓度的变化跨越三个数量级，而FA浓度在研究的pH范围内变化一个数量级。相关性分析强烈表明，在研究的18种土壤中，HA在随着pH值升高增加溶液中铜和铅浓度方面起主要作用。尽管FA浓度随着pH值的升高而增加，并且在较低pH值（pH = 3 - 5）时其浓度大于HA组分的浓度，但在很宽的pH范围内，由FA导致的有机碳百分比几乎是恒定的。因此，在酸性更强的环境中，FA在控制有机金属相互作用方面可能比HA发挥更大的作用。对于镉、镍和锌，解吸/溶解模式显示在低pH值时溶液中金属浓度较高，在极高pH值（pH>10）时溶液浓度略有增加。此处给出的结果表明，溶解性有机碳对镉、镍和锌的迁移的影响可能仅发生在由非常高的pH值控制的系统中。在高pH值时，在本研究中很难区分这些阳离子在溶液相中的浓度略有增加是由于DOC还是水解反应。这些高pH值环境在自然环境中很少出现。
