The arsenic-contaminated groundwater has attracted attention in much south and southeast Asian deltas, however, mainly on the deep aquifers. Here, arsenic (As) concentration and its fractionation of the sediment cores in a shallow aquifer in Bangladesh were investigated using ICP-MS, FE-EPMA, XRD and ¹⁴C-AMS chronology techniques. The results of the present study indicated that the peak concentrations of As (54.7–79.1 µg/g) were in peat layers (at a depth of 7.5–8.0 m). Several types of iron (oxyhidr)oxides and framboidal pyrite, which contain As also, were found in the peat samples. The high concentrations of As were in an exchangeable form, As-bearing iron crystalline and As-bearing organic materials. We revealed that the As-rich peat layers were formed from 3170 to 3901 cal yrs before, due to the sea level decrease in this area. The 16S rRNA gene-based phylogenetic analysis revealed that the bacterial strains in the As-rich peats were mainly affiliated with genera Acinetobacter, Enterobacter, Escherichia, Bacillus, Clostridiaceae and Acinetobacter. The geo-accumulation index (I_geo) and ecological risk index assessment were calculated for the sediments, which shows that As-rich sediment layers were in range of moderately to heavily contaminated and considerable classes, respectively. Under the permanent saturated condition, the As-rich peat layers should be considered as an important potential driver of the groundwater As in this area.

然而，砷污染的地下水在南亚和东南亚的许多三角洲引起了人们的关注，但主要集中在深层含水层。^{在这里，使用 ICP-MS、FE-EPMA、XRD 和14}研究了孟加拉国浅层含水层中沉积物岩心的砷 (As) 浓度及其分馏。C-AMS 年表技术。本研究的结果表明，As 的峰值浓度（54.7–79.1 µg/g）位于泥炭层中（深度为 7.5–8.0 m）。在泥炭样品中发现了几种类型的铁（氧氢化物）氧化物和含有 As 的黄铁矿。高浓度的 As 以可交换形式、含 As 铁结晶和含 As 有机材料的形式存在。我们发现，由于该地区海平面下降，富含砷的泥炭层形成于 3170 至 3901 cal 年前。基于16S rRNA基因的系统发育分析表明，富As泥炭中的菌株主要隶属于不动杆菌属、肠杆菌属、大肠埃希菌属、芽孢杆菌属、梭菌科和不动杆菌属。对沉积物进行地质积累指数（I _geo）和生态风险指数评价，结果表明，富As沉积层分别处于中度至重度污染和相当大的污染等级。在永久饱和条件下，富砷泥炭层应被视为该地区地下水砷的重要潜在驱动因素。