Hydrochemical and Fluorescent Spectroscopic Evidences of Arsenic Mobilization in Groundwater
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摘要: 为了认识高砷地下水中砷活化迁移的生物地球化学机制，对江汉平原地下水氧化还原敏感元素的水化学特征及溶解性有机物(DOM)三维荧光信息进行了研究.水化学研究显示，地下水中的砷与铁的还原和有机质的氧化分解过程有密切关系.水样DOM的三维荧光分析表明，地下水中存在微生物介导下氧化还原过程的反应性有机物组分，其中醌类腐殖质与铁、硫酸盐等的还原反应过程联系紧密.还原、氧化醌类及易降解DOM组分与还原产物、砷的关系进一步显示，砷的活化与微生物介导下的铁氧化物的还原过程联系在一起.在这一过程中，易降解有机物充当电子供体的角色并被消耗，而还原醌与氧化醌则很可能扮演了电子飞行过程中的电子飞行物，"催化"了砷活化的氧化还原过程.Abstract: The investigation of redox-sensitive elements characteristics and 3D fluorescent spectroscopy to groundwater from JiangHan plain, were conducted to understand the biogeochemical mechanisms of arsenic mobilization. Groundwater geochemistry indicates that the occurrence of arsenic is closely associated with the geochemical processes of Fe (Ⅲ) reduction and organic matter oxidation. The fluorescent spectroscopy characterization of dissolved organic matter (DOM) shows that the reactive organic matters mediating oxidation-reduction reaction prevail in groundwater and arsenic mobilization is linked with the microbes-mediated reductive dissolution process of iron (hydr)oxides, in which DOM components are probably involved in the process electron shuttle and thus enhance arsenic mobilization through catalyzing the oxidation-reduction process.
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图 1 研究区位置、地表沉积物地质成因和地下水采样点分布
1.全新统冲积；2.全新统冲湖积；3.全新统湖沼积；4.全新统湖积；5.全新统坡积-冲积；6.晚更新统冲湖积；7.地下水采样点
Fig. 1. The location and the surface geology in the study area
图 3 氧化还原敏感组分浓度关系
a.NH4+-NO3-；b.S2--SO42-；c.Fe2+-Fediss；d.HCO3--Fediss
Fig. 3. Relationship between redox sensitive element species
图 4 溶解态砷与铁、Eh及有机氮的关系
a.溶解态As-Fe-Eh三元关系；b.溶解态砷与有机碳关系
Fig. 4. Relationship of Eh with dissolved iron and dissolved arsenic with organic carbon
图 5 铁矿物的饱和指数变化统计描述
Fig. 5. Statistical description of saturation index for specific mineral iron species
图 6 平行因子分析法解析后得到的溶解性有机物组分三维荧光谱图
Fig. 6. 3D fluorescence spectrum of DOM components determined by PARAFAC method
图 7 DOM腐殖质醌类组分与溶解态砷的关系
Fig. 7. Relationship between humic quinones and dissolved arsenic
表 1 研究区地下水样品化学指标统计结果
Table 1. Statistical descriptions of groundwater chemical parameters
化学指标 单位 平均值 最大值 最小值 pH 7.2 8.3 6.5 Eh mv 16.4 120.3 -96.2 EC μS/cm 756 1 576 241 Na+ mg/L 22.8 80.1 3.7 K+ mg/L 2.21 23.30 0.29 Ca2+ mg/L 60.4 126.7 19.6 Mg2+ mg/L 29.2 54.8 5.1 Fedissolved mg/L 7.48 18.94 0.27 Fe2+ mg/L 6.04 15.77 0.22 Asdissolved μg/L 67.22 972.93 0.93 Cl- mg/L 10.46 74.40 2.23 HCO3- mg/L 371 563 55 NO3- mg/L 33.3 119.0 0.8 SO42- mg/L 20.5 187.9 3.4 S2- μg/L 12.35 34.00 5.00 NH4+ mg/L 1.61 13.81 0.04 SiO2 mg/L 14.31 19.78 6.39 DOC mg/L 3.1 10.4 0.7 
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表 2 三维荧光-平行因子分析确定的DOM荧光组分
Table 2. DOM components identified by fluorescent EEM & PARAFAC
组分编号 最大激发/发射波长 相似的有机物化学分类或化合物 参考文献 陆生腐殖质组分C1 320(250)/416 C10:310(＜250)/426;
阿魏酸: 310(＜250)/418Stedmon and Markager(2005);
Cory and McKnight(2005)陆生腐殖质组分C2 360(260)/440 未找到性质相似的对应化合物 Stedmon and Markager(2005) 微生物腐殖质组分C3 270(380)/484 SQ2: 270(375)/462微生物源的还原性醌类 Stedmon and Markager (2005) 微生物腐殖质组分C4 230(300)/426 Q3:＜250(300)/388微生物源的氧化性醌类;
香草醛: 310/430Stedmon and Markager (2005);
Cory and McKnight (2005)蛋白类(色氨酸)组分C5 280/350 C8:270/350，微生物源色氨酸;
L-色氨酸: 280/356Stedmon and Markager (2005);
Cory and McKnight (2005)
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表 3 DOM组分相对浓度与氧化还原敏感组分的相关性
Table 3. Correlation relationship between the relative concentration of DOMs and redox sensitive elements
类别 Asdiss Fediss Fe2+ HCO3- DOC S2- 类腐殖质C1 0.53 0.37 0.24 0.27 0.79 0.28 类腐殖质C2 0.54 0.37 0.24 0.30 0.79 0.25 腐殖类还原醌C3 0.55 0.41 0.47 0.21 0.81 0.42 腐殖类氧化醌C4 0.47 0.28 - 0.20 0.48 0.06 易降解DOM C5 0.25 - - - 0.34 - 注："-"表示负相关或者无相关，斜黑体表示本研究重点关注的信息. 吻合.这些信息均显示了砷的活化与微生物介导下铁氢氧化物的还原过程有关，而这一过程中，易降解有机物充当电子供体的角色并被消耗，而还原醌与氧化醌则很可能扮演了电子飞行过程中的飞行物，起到"催化"氧化还原反应的作用.
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