Wilkin Richard T, Lee Tony R, Beak Douglas G, Anderson Robert, Burns Betsy
U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Groundwater, Watershed, and Ecosystem Restoration Division, 919 Kerr Research Drive, Ada, OK 74820, United States.
Hydrometrics Inc., 3020 Bozeman Avenue, Helena, MT 59601, United States.
Appl Geochem. 2018 Feb 1;89:255-264. doi: 10.1016/j.apgeochem.2017.12.011.
Co-contaminant behavior of arsenic (As) and selenium (Se) in groundwater is examined in this study at a former lead and zinc smelting facility. We collected water quality data, including concentrations of trace metals, major ions, and metalloid speciation, over a 15-year period to document long-term trends and relationships between As, Se, geochemical parameters, and other redox-sensitive trace metals. Concentrations of dissolved As and Se were negatively correlated (Kendall's Tau B correlation coefficient, r = -0.72) and showed a distinctive L-shaped relationship. High-concentration arsenic wells (>5 mg L) were characterized by intermediate oxidation-reduction conditions (75 < Eh < 275 mV), near-neutral pH (6.1-7.9), low Ca/Na ratios, elevated Fe and Mn concentrations, and high proportions of As(III) relative to total dissolved As. High-concentration Se wells (>500 μg L) were characterized by more positive Eh (305-500 mV), low Fe concentrations, and high proportions of As(V). Batch micocosm experiments showed that aquifer solids contain mineral surfaces and/or microbial communities capable of removing selenate from groundwater. Electron microprobe and Se -edge X-ray absorption near-edge spectroscopic analyses demonstrated that Se was predominantly associated with elemental Se in the reduced aquifer solids. Factor analysis revealed three discernible groupings of trace metals. Group I includes U, Se, and nitrate-N, all of which are mobile under oxygenated to moderately oxygenated conditions. Group II includes elements that are mobile under Fe(III)-reducing conditions: Fe, total dissolved As, As(III), and ammonium-N. Group III elements (Mo, Sb, and V) showed mobility across the entire range of redox conditions encountered in site groundwater; As(V) clustered with this group of elements. Geochemical modeling suggests that As and Se species were in a state of disequilibrium with respect to measured parameters indicative of redox conditions, although predicted patterns of redox-controlled mobility and attenuation were confirmed. This analysis is important to better understand groundwater contaminant behavior in response to redox conditions ranging from oxic/suboxic to Fe(III)-reducing, but excluding sulfate-reducing conditions.
本研究在一个 former lead and zinc smelting facility 对地下水中砷（As）和硒（Se）的共污染行为进行了研究。我们在 15 年的时间里收集了水质数据，包括痕量金属浓度、主要离子和类金属形态，以记录 As、Se、地球化学参数以及其他对氧化还原敏感的痕量金属之间的长期趋势和关系。溶解态 As 和 Se 的浓度呈负相关（肯德尔 Tau B 相关系数，r = -0.72），并呈现出独特的 L 形关系。高浓度砷井（>5 mg/L）的特征是中等氧化还原条件（75 < Eh < 275 mV）、近中性 pH（6.1 - 7.9）、低 Ca/Na 比、Fe 和 Mn 浓度升高以及 As(III)相对于总溶解态 As 的比例较高。高浓度 Se 井（>500 μg/L）的特征是 Eh 更正（305 - 500 mV）、Fe 浓度低以及 As(V)比例高。批次微宇宙实验表明，含水层固体含有能够从地下水中去除硒酸盐的矿物表面和/或微生物群落。电子微探针和 Se - 边缘 X 射线吸收近边光谱分析表明，在还原的含水层固体中，Se 主要与元素 Se 相关。因子分析揭示了痕量金属的三个可辨别的分组。第一组包括 U、Se 和硝酸盐 - N，所有这些在氧化至中度氧化条件下都是可移动的。第二组包括在 Fe(III)还原条件下可移动的元素：Fe、总溶解态 As、As(III)和铵 - N。第三组元素（Mo、Sb 和 V）在场地地下水中遇到的整个氧化还原条件范围内都表现出可移动性；As(V)与这组元素聚集在一起。地球化学模型表明，尽管氧化还原控制的迁移和衰减的预测模式得到了证实，但 As 和 Se 物种相对于指示氧化还原条件的测量参数处于不平衡状态。该分析对于更好地理解从有氧/亚氧到 Fe(III)还原（但不包括硫酸盐还原条件）的氧化还原条件下的地下水污染物行为很重要。
