State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, 129 Luoyu Road, Wuhan, 430079, China.
College of Plant Science and Technology, Huazhong Agricultural University, Shizishan Street-1, Wuhan, 430070, Hubei, China; Department of Agriculture, University of Swabi, Khyber Pakhtunkhwa, Pakistan.
J Environ Manage. 2020 May 15;262:110318. doi: 10.1016/j.jenvman.2020.110318. Epub 2020 Mar 3.
Groundwater with an excessive level of Arsenic (As) is a threat to human health. In Bangladesh, out of 64 districts, the groundwater of 50 and 59 districts contains As exceeding the Bangladesh (50 μg/L) and WHO (10 μg/L) standards for potable water. This review focuses on the occurrence, origin, plausible sources, and mobilization mechanisms of As in the groundwater of Bangladesh to better understand its environmental as well as public health consequences. High As concentrations mainly was mainly occur from the natural origin of the Himalayan orogenic tract. Consequently, sedimentary processes transport the As-loaded sediments from the orogenic tract to the marginal foreland of Bangladesh, and under the favorable biogeochemical circumstances, As is discharged from the sediment to the groundwater. Rock weathering, regular floods, volcanic movement, deposition of hydrochemical ore, and leaching of geological formations in the Himalayan range cause As occurrence in the groundwater of Bangladesh. Redox and desorption processes along with microbe-related reduction are the key geochemical processes for As enrichment. Under reducing conditions, both reductive dissolution of Fe-oxides and desorption of As are the root causes of As mobilization. A medium alkaline and reductive environment, resulting from biochemical reactions, is the major factor mobilizing As in groundwater. An elevated pH value along with decoupling of As and HCO plays a vital role in mobilizing As. The As mobilization process is related to the reductive solution of metal oxides as well as hydroxides that exists in sporadic sediments in Bangladesh. Other mechanisms, such as pyrite oxidation, redox cycling, and competitive ion exchange processes, are also postulated as probable mechanisms of As mobilization. The reductive dissolution of MnOOH adds dissolved As and redox-sensitive components such as SO and oxidized pyrite, which act as the major mechanisms to mobilize As. The reductive suspension of Mn(IV)-oxyhydroxides has also accelerated the As mobilization process in the groundwater of Bangladesh. Infiltration from the irrigation return flow and surface-wash water are also potential factors to remobilize As. Over-exploitation of groundwater and the competitive ion exchange process are also responsible for releasing As into the aquifers of Bangladesh.
地下水砷含量过高会威胁人类健康。在孟加拉国，64 个区中有 50 个区和 59 个区的地下水砷含量超过孟加拉国（50μg/L）和世界卫生组织（10μg/L）饮用水标准。本综述重点关注孟加拉国地下水砷的发生、来源、可能的来源和迁移机制，以更好地了解其环境和公共卫生后果。高砷浓度主要来自喜马拉雅造山带的自然起源。因此，沉积过程将负载砷的沉积物从造山带输送到孟加拉国的前缘，在有利的生物地球化学条件下，砷从沉积物中排放到地下水中。岩石风化、定期洪水、火山活动、化学矿床的沉积以及喜马拉雅山脉地质构造的淋滤都会导致孟加拉国地下水中砷的存在。氧化还原和解吸过程以及与微生物相关的还原是砷富集的关键地球化学过程。在还原条件下，铁氧化物的还原溶解和砷的解吸都是砷迁移的根本原因。生化反应产生的中碱性和还原性环境是地下水砷迁移的主要因素。升高的 pH 值以及砷和 HCO 的解耦在砷的迁移中起着至关重要的作用。砷的迁移过程与金属氧化物和氢氧化物的还原溶液有关，这些氧化物和氢氧化物存在于孟加拉国零星的沉积物中。其他机制，如黄铁矿氧化、氧化还原循环和竞争离子交换过程，也被认为是砷迁移的可能机制。MnOOH 的还原溶解增加了溶解的砷和氧化还原敏感成分，如 SO 和氧化黄铁矿，这些是砷迁移的主要机制。Mn(IV)-oxyhydroxides 的还原悬浮也加速了孟加拉国地下水的砷迁移过程。灌溉回流水和地表冲洗水的渗透也是重新迁移砷的潜在因素。地下水的过度开采和竞争离子交换过程也是导致孟加拉国含水层释放砷的原因。
