Contribution of sedimentary organic matter to arsenic mobilization along a potential natural reactive barrier (NRB) near a river: The Meghna river, Bangladesh
Contribution of sedimentary organic matter to arsenic mobilization along a potential natural reactive barrier (NRB) near a river: The Meghna river, Bangladesh
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沉积有机质对河流附近潜在天然反应屏障 (NRB) 砷迁移的贡献：孟加拉国梅格纳河
DOI：
10.1016/j.chemosphere.2022.136289
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发表时间：
2022
期刊：
影响因子：
8.8
通讯作者：
Ahmed, Kazi M.
中科院分区：
文献类型：
--
作者：
Varner, Thomas S.;Kulkarni, Harshad V.;Nguyen, William;Kwak, Kyungwon;Cardenas, M Bayani;Knappett, Peter S.K.;Ojeda, Ann S.;Malina, Natalia;Bhuiyan, Mesbah Uddin;Ahmed, Kazi M.
孟加拉国浅层含水层中溶解砷 (As) 浓度升高的主要原因是在富含有机物 (OM) 的还原性环境中微生物介导的含砷铁 (Fe) (氧) 氢氧化物的还原。沿着孟加拉国梅格纳河，河流与潜流区内地下水之间的相互作用导致氧化还原条件波动，从而形成能够螯合砷的富铁天然反应屏障 (NRB)。为了了解 NRB 对砷迁移率的影响，对河岸沉积物（<3 m 深度）和下面的含水层沉积物（深度达 37 m）的地球化学进行了分析。进行了 24 小时沉积物-水提取实验，以模拟这些沉积物与含氧河水的相互作用。分析沉积物和沉积物-水提取物的无机和有机化学参数。结果显示，河岸和含水层沉积物的元素组成没有差异，分别含有 40 ± 12 g/kg 的 Fe 和 7 ± 2 mg/kg 的 As。然而，河岸沉积物和含水层沉积物中提取的无机和有机成分的量却存在显着差异。水从河岸沉积物中提取了 6.4 ± 16.1 mg/kg 的 Fe 和 0.03 ± 0.02 mg/kg 的 As，而从含水层沉积物中提取了 154.0 ± 98.1 mg/kg 的 Fe 和 0.55 ± 0.40 mg/kg 的 As。河岸和含水层沙子含有相似数量的沉积有机质 (SOM) (17,705.2 ± 5157.6 毫克/千克)。然而，SOM 的水提取部分变化很大，即河岸沙中为 67.4 ± 72.3 mg/kg，含水层沙中为 1330.3 ± 226.6 mg/kg。详细表征表明，河岸 SOM 呈蛋白质状、新鲜、低分子量且不稳定，而含水层砂中的 SOM 呈腐殖质状、年代久远、高分子量且顽固。在旱季，河岸的含氧条件可能会促进有氧代谢，限制砷在 NRB 内的流动性。
Elevated dissolved arsenic (As) concentrations in the shallow aquifers of Bangladesh are primarily caused by microbially-mediated reduction of As-bearing iron (Fe) (oxy)hydroxides in organic matter (OM) rich, reducing environments. Along the Meghna River in Bangladesh, interactions between the river and groundwater within the hyporheic zone cause fluctuating redox conditions responsible for the formation of a Fe-rich natural reactive barrier (NRB) capable of sequestering As. To understand the NRB's impact on As mobility, the geochemistry of riverbank sediment (<3 m depth) and the underlying aquifer sediment (up to 37 m depth) was analyzed. A 24-hr sediment-water extraction experiment was performed to simulate interactions of these sediments with oxic river water. The sediment and the sediment-water extracts were analyzed for inorganic and organic chemical parameters. Results revealed no differences between the elemental composition of riverbank and aquifer sediments, which contained 40 ± 12 g/kg of Fe and 7 ± 2 mg/kg of As, respectively. Yet the amounts of inorganic and organic constituents extracted were substantially different between riverbank and aquifer sediments. The water extracted 6.4 ± 16.1 mg/kg of Fe and 0.03 ± 0.02 mg/kg of As from riverbank sediments, compared to 154.0 ± 98.1 mg/kg of Fe and 0.55 ± 0.40 mg/kg of As from aquifer sediments. The riverbank and aquifer sands contained similar amounts of sedimentary organic matter (SOM) (17,705.2 ± 5157.6 mg/kg). However, the water-extractable fraction of SOM varied substantially, i.e., 67.4 ± 72.3 mg/kg in riverbank sands, and 1330.3 ± 226.6 mg/kg in aquifer sands. Detailed characterization showed that the riverbank SOM was protein-like, fresh, low molecular weight, and labile, whereas SOM in aquifer sands was humic-like, older, high molecular weight, and recalcitrant. During the dry season, oxic conditions in the riverbank may promote aerobic metabolisms, limiting As mobility within the NRB.