Mineralogical and geomicrobiological investigations on groundwater arsenic enrichment in Bangladesh
Mineralogical and geomicrobiological investigations on groundwater arsenic enrichment in Bangladesh
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DOI：
10.1016/j.apgeochem.2003.09.008
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发表时间：
2004-02-01
影响因子：
3.4
通讯作者：
Akai, K
中科院分区：
文献类型：
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作者：
Akai, J;Izumi, K;Akai, K
本研究对恒河沉积物中砷的来源及其在地下水中释放的微生物机制进行了研究，作者使用 XRD、TEM-EDS 和 EPMA 技术系统地研究了沉积物中存在的相关矿物种类。结果显示，孟加拉国西部的恒河沉积物中存在多种含砷矿物。硫化铁矿物由近无定形和/或结晶的草莓状黄铁矿和均含有砷的黄铁矿前体组成。在泥质沉积物中还发现了几种类型的氢氧化铁（氧化物），其中含有不同数量的砷。 As的含量从Fe氧化物到草莓状黄铁矿和黄铁矿的前体不断增加。测定了岩心沉积物中砷的四种不同化学形式。依次提取的化学形态如下：（1）酸溶形式（主要固定在碳酸盐中），（2）还原形式（固定在铁和/或锰氧化物中），（3）有机形式，（4）不溶形式（主要固定在硫化物中，很少固定在硅酸盐矿物中）。在大多数样品中，砷主要吸附在铁和/或锰氧化物、有机形式和硫化物矿物上，尽管不同样品中砷的相对丰度不同。进行地质微生物培养实验是为了检验微生物过程在地下水中砷释放中发挥关键作用的假设。利用孟加拉国的沉积物设计了批量培养和循环水系统实验。在批量实验中，在以 N-2 为主的气氛下添加含有葡萄糖、多肽蛋白和酵母提取物、尿素和肥料的营养物几天后，As 以低 Eh 值释放。这与没有营养物的对照实验形成对比。 N-2 气氛中沙层的循环水实验也显示出类似的结果。这些结果支持微生物过程在还原条件下介导砷释放到地下水中的假设。实验中使用的葡萄糖和聚蛋白胨可能分别对应于碳源和氮源。较年轻的沉积物含有丰富的有机物，很容易被细菌利用。因此，增强的细菌活性可能对应于使用有机物模拟加速自然成岩过程，或某些肥料/废水效应。 (C) 2003 Elsevier Ltd. 保留所有权利。
Sources of As in the Ganges sediments and microbial mechanisms of its release in groundwater were examined in the present study, where the authors have systematically examined the pertinent mineral species present in the sediments using XRD, TEM-EDS and EPMA techniques. The results show several As-bearing minerals in the Ganges sediments, in western Bangladesh. Iron-sulfide minerals consist of near-amorphous and/or crystalline precursors of framboidal pyrite and pyrite both of which contain As. Several types of Fe oxyhydroxides (oxides), which contain variable amounts of As were also found in muddy sediments. The content of As increases from Fe-oxides to the precursors of framboidal pyrite and pyrite. Four different chemical forms of As from the core sediments were determined. The sequentially extracted chemical forms are as follows: (1) acid soluble form (As mainly fixed in carbonates), (2) reducible form (As fixed in Fe- and/or Mn-oxides), (3) organic form, (4) insoluble form (As fixed mainly in sulfide and rarely in silicate minerals). Arsenic is dominantly sorbed on to Fe- and/or Mn-oxides, organic forms and sulfide minerals in most samples, although their relative abundances differ in different samples. Geomicrobial culture experiments were carried out to test the hypothesis that microbial processes play a key role in the release of As in groundwater. Batch culture and circulating water system experiments were designed using the sediments from Bangladesh. In the batch experiments, As was released at low Eh values a few days after adding nutrients containing glucose, polypepton and yeast extract, urea and fertilizer under a dominantly N-2 atmosphere. This contrasts with the control experiments without nutrients. Circulating water experiments with sand layer in a N-2 atmosphere showed similar results. These results support the hypothesis that microbial processes mediate the release of As into groundwater under reducing conditions. Glucose and polypepton used in the experiments may correspond to C and N sources, respectively. Younger sediments contain abundant organic matter, which is easily used by bacteria. So, the enhanced bacterial activity may correspond to simulation of accelerated natural diagenetic process using organic matter, or some fertilizer/wastewater effects. (C) 2003 Elsevier Ltd. All rights reserved.